Work functioning in cancer patients: looking beyond return to work
Dorland, H.F.
IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.
Document Version
Publisher's PDF, also known as Version of record
Publication date: 2018
Link to publication in University of Groningen/UMCG research database
Citation for published version (APA):
Dorland, H. F. (2018). Work functioning in cancer patients: looking beyond return to work. University of Groningen.
Copyright
Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).
Take-down policy
If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.
GEN
ERAL
DIS
CUSS
This thesis aims to expand our knowledge of cancer patients’ health-related work functioning during the first 18 months after return to work, with regard to health, psychosocial and work-related factors. The thesis contains the first longitudinal study on work functioning in cancer patients, a novel work outcome that goes beyond return to work and employment status. More accurately monitoring a cancer patient’s work functioning is relevant for the cancer patient, the (occupational) physician, the employer and society at large. In this general discussion, the main findings of this thesis are summarized and discussed. The methodological issues and implications for both practice and future research are addressed.
Main findings
The main findings are summarized per research objective.
Research objective 1 (Chapter 2): to identify barriers and facilitators of work functioning
among cancer patients after return to work.
Cancer patients and occupational health professionals mentioned the impact of cancer symptoms (i.e. cognitive symptoms, fatigue) and the adaptation to the new situation after cancer diagnosis as barriers to work functioning. Other barriers were: lack of support from the supervisor and colleagues, changes in the work environment and new colleagues who are not familiar with the situation. In contrast, high social support from the supervisor and colleagues, open communication between the cancer patient and the supervisor (e.g. about work accommodations and decision latitude) and staying at work during treatment were mentioned by cancer patients and occupational health professionals as facilitators of work functioning.
Research objective 2 (Chapter 3): to cross-culturally translate and adapt the Cognitive Symptom Checklist-Work21 into Dutch and to assess the reliability and validity of the CSC-W Dutch version.
The CSC-W21 was cross-culturally translated and adapted into Dutch, resulting in the CSC-W Dutch Version (CSC-W DV). The CSC-W DV contains 19 items and has new response anchors. The CSC-W DV was validated in a cohort of working cancer patients and two subscales were identified: a ‘working memory’ subscale (containing 8 items from the original ‘working
memory’ subscale) and an ‘executive function’ subscale (containing 11 items from the original ‘executive function’ and ‘task completion’ subscales). Hypothesis testing showed that cancer patients with higher levels of self-reported cognitive symptoms at work, reported lower levels of work functioning and higher levels of fatigue and depressive symptoms.
Research objective 3 (Chapter 4):to identify work functioning trajectories in the year following return to work of cancer patients and to examine baseline socio-demographic, health-related and work-related variables associated with work functioning trajectories.
Three distinct work functioning trajectories in the year following return to work were identified: ‘persistently high’ (16% of the sample), ‘moderate to high’ (52%) and ‘persistently low’ work functioning (32%). Cancer patients with persistently high work functioning reported a shorter time between diagnosis and return to work and more often good to excellent health compared to the other trajectories. Cancer patients with persistently low work functioning reported higher levels of baseline work-specific cognitive symptoms compared to cancer patients in the other trajectories. As cancer type and cancer treatment were not associated with any work functioning trajectory, they may be less important for managing work functioning of cancer patients who have returned to work.
Research objective 4 (Chapter 5):to investigate the course of work functioning, health status, and work-related factors in cancer patients during 18 months after return to work and to examine the associations between these variables and work functioning over time.
Cancer patients reported an increase in work functioning and decreases in fatigue and depressive symptoms in the first 12 months after return to work, followed by a stable course from months 12 to 18 for all three constructs. Work-specific cognitive symptoms were stable during the first 18 months post return to work. Working hours increased during the first 6 months, while supervisor and colleague social support decreased. Working hours and supervisor and colleague social support remained stable in the following 12 months.
When examining the associations with work functioning over time, a decrease of fatigue, depressive symptoms and work-specific cognitive symptoms and an increase of working hours and supervisor social support were associated with an increase of work functioning over time.
This thesis aims to expand our knowledge of cancer patients’ health-related work functioning during the first 18 months after return to work, with regard to health, psychosocial and work-related factors. The thesis contains the first longitudinal study on work functioning in cancer patients, a novel work outcome that goes beyond return to work and employment status. More accurately monitoring a cancer patient’s work functioning is relevant for the cancer patient, the (occupational) physician, the employer and society at large. In this general discussion, the main findings of this thesis are summarized and discussed. The methodological issues and implications for both practice and future research are addressed.
Main findings
The main findings are summarized per research objective.
Research objective 1 (Chapter 2): to identify barriers and facilitators of work functioning
among cancer patients after return to work.
Cancer patients and occupational health professionals mentioned the impact of cancer symptoms (i.e. cognitive symptoms, fatigue) and the adaptation to the new situation after cancer diagnosis as barriers to work functioning. Other barriers were: lack of support from the supervisor and colleagues, changes in the work environment and new colleagues who are not familiar with the situation. In contrast, high social support from the supervisor and colleagues, open communication between the cancer patient and the supervisor (e.g. about work accommodations and decision latitude) and staying at work during treatment were mentioned by cancer patients and occupational health professionals as facilitators of work functioning.
Research objective 2 (Chapter 3): to cross-culturally translate and adapt the Cognitive Symptom Checklist-Work21 into Dutch and to assess the reliability and validity of the CSC-W Dutch version.
The CSC-W21 was cross-culturally translated and adapted into Dutch, resulting in the CSC-W Dutch Version (CSC-W DV). The CSC-W DV contains 19 items and has new response anchors. The CSC-W DV was validated in a cohort of working cancer patients and two subscales were identified: a ‘working memory’ subscale (containing 8 items from the original ‘working
memory’ subscale) and an ‘executive function’ subscale (containing 11 items from the original ‘executive function’ and ‘task completion’ subscales). Hypothesis testing showed that cancer patients with higher levels of self-reported cognitive symptoms at work, reported lower levels of work functioning and higher levels of fatigue and depressive symptoms.
Research objective 3 (Chapter 4):to identify work functioning trajectories in the year following return to work of cancer patients and to examine baseline socio-demographic, health-related and work-related variables associated with work functioning trajectories.
Three distinct work functioning trajectories in the year following return to work were identified: ‘persistently high’ (16% of the sample), ‘moderate to high’ (52%) and ‘persistently low’ work functioning (32%). Cancer patients with persistently high work functioning reported a shorter time between diagnosis and return to work and more often good to excellent health compared to the other trajectories. Cancer patients with persistently low work functioning reported higher levels of baseline work-specific cognitive symptoms compared to cancer patients in the other trajectories. As cancer type and cancer treatment were not associated with any work functioning trajectory, they may be less important for managing work functioning of cancer patients who have returned to work.
Research objective 4 (Chapter 5):to investigate the course of work functioning, health status, and work-related factors in cancer patients during 18 months after return to work and to examine the associations between these variables and work functioning over time.
Cancer patients reported an increase in work functioning and decreases in fatigue and depressive symptoms in the first 12 months after return to work, followed by a stable course from months 12 to 18 for all three constructs. Work-specific cognitive symptoms were stable during the first 18 months post return to work. Working hours increased during the first 6 months, while supervisor and colleague social support decreased. Working hours and supervisor and colleague social support remained stable in the following 12 months.
When examining the associations with work functioning over time, a decrease of fatigue, depressive symptoms and work-specific cognitive symptoms and an increase of working hours and supervisor social support were associated with an increase of work functioning over time.
Research objective 5 (Chapter 6):to describe the course of work-specific cognitive symptoms in the first 18 months post return to work and to examine the associations of work characteristics, fatigue and depressive symptoms with work-specific cognitive symptoms over time.
During the first 18 months post return to work, cancer patients reported higher levels of working memory symptoms compared to executive function symptoms; both constructs remained stable during this period. Cancer patients with both manual and non-manual job tasks reported lower levels of work-specific cognitive symptoms over time, compared to cancer patients with only non-manual job tasks. During 18 months follow-up, higher levels of depressive symptoms were related to reporting higher levels of overall work-specific cognitive symptoms; higher levels of fatigue were related to reporting higher levels of working memory symptoms.
Discussion of the main findings
A main finding of this thesis is that a majority of the cancer patients reported moderate to high work functioning after return to work, while one-third of the cancer patients reported lower levels of work functioning. When back at work, long-lasting problems were experienced by cancer patients, such as fatigue, depressive symptoms and cognitive symptoms. While fatigue and depressive symptoms decreased over time, work-specific cognitive symptoms remained stable after return to work. In the following sections, the main findings are discussed and compared with other studies.
Measuring work functioning and work-specific cognitive symptoms fills a knowledge gap in cancer and work research
This thesis is based on the first longitudinal study on health-related work functioning of cancer patients after return to work, the WOrk LIfe after Cancer (WOLICA) study. A recent systematic review on ongoing physical and/or psychosocial problems related to the functioning of employees with a history of cancer in the post-return to work phase, which was published during the conduct of our study, concluded that attention for the expanding group of cancer
patients at work is limited1. Duijts et al. argued that it is critical to consider work functioning beyond the initial return to work, as part of sustainable return to work2. As WOLICA addresses a novel work outcome - work functioning - that goes beyond the simple dichotomy of return to work yes/no, the studies in this thesis can be viewed as a major and innovative contribution to the current literature. Knowledge about the cancer patient’s work functioning over time and the associated factors helps to guide and support cancer patients, to enhance sustainable return to work. Insight into cancer patients’ performance of work tasks when (back) at work is of utmost importance for (occupational) physicians and employers to identify cancer patients that need additional guidance and support after return to work.
In a current perspective on cancer-related cognitive impairment and ability to work, also published during the conduct of our study, Duijts et al. mentioned that the impact of cancer-related cognitive impairment on work-related outcomes in cancer survivors to date is not well-understood3. To better understand the impact, the authors stressed the importance of using a self-report instrument, such as the CSC-W DV, to measure cognitive functioning at work. Using a self-report instrument is important, as it takes into account the environment where a person is situated and interactions with the workplace and colleagues4. A better understanding of the impact of persistent physical and psychosocial problems on cancer patients at work may help to develop effective treatment strategies and more effective workplace interventions for cancer patients at work5.
Improvements in work functioning during 18 months after return to work
Measuring work functioning during a period of 18 months after return to work provides insight in the experienced difficulties in meeting the demands at work and in the course of these difficulties over time. Cancer patients showed improvements in their work functioning in the first 12 months after return to work. After this improvement, the average work functioning level was similar to the work functioning level in the general working population9. Work functioning remains stable in the period between 12 and 18 months. The improvements in work functioning are in line with the gradual return to work approach, whereby an occupational physician and a cancer patient in consultation decide how much work and what kind of work someone can do. However, work functioning did not improve in all cancer patients. Approximately, one-third of the cancer patients experienced persistently low work functioning after return to work.
Research objective 5 (Chapter 6):to describe the course of work-specific cognitive symptoms in the first 18 months post return to work and to examine the associations of work characteristics, fatigue and depressive symptoms with work-specific cognitive symptoms over time.
During the first 18 months post return to work, cancer patients reported higher levels of working memory symptoms compared to executive function symptoms; both constructs remained stable during this period. Cancer patients with both manual and non-manual job tasks reported lower levels of work-specific cognitive symptoms over time, compared to cancer patients with only non-manual job tasks. During 18 months follow-up, higher levels of depressive symptoms were related to reporting higher levels of overall work-specific cognitive symptoms; higher levels of fatigue were related to reporting higher levels of working memory symptoms.
Discussion of the main findings
A main finding of this thesis is that a majority of the cancer patients reported moderate to high work functioning after return to work, while one-third of the cancer patients reported lower levels of work functioning. When back at work, long-lasting problems were experienced by cancer patients, such as fatigue, depressive symptoms and cognitive symptoms. While fatigue and depressive symptoms decreased over time, work-specific cognitive symptoms remained stable after return to work. In the following sections, the main findings are discussed and compared with other studies.
Measuring work functioning and work-specific cognitive symptoms fills a knowledge gap in cancer and work research
This thesis is based on the first longitudinal study on health-related work functioning of cancer patients after return to work, the WOrk LIfe after Cancer (WOLICA) study. A recent systematic review on ongoing physical and/or psychosocial problems related to the functioning of employees with a history of cancer in the post-return to work phase, which was published during the conduct of our study, concluded that attention for the expanding group of cancer
patients at work is limited1. Duijts et al. argued that it is critical to consider work functioning beyond the initial return to work, as part of sustainable return to work2. As WOLICA addresses a novel work outcome - work functioning - that goes beyond the simple dichotomy of return to work yes/no, the studies in this thesis can be viewed as a major and innovative contribution to the current literature. Knowledge about the cancer patient’s work functioning over time and the associated factors helps to guide and support cancer patients, to enhance sustainable return to work. Insight into cancer patients’ performance of work tasks when (back) at work is of utmost importance for (occupational) physicians and employers to identify cancer patients that need additional guidance and support after return to work.
In a current perspective on cancer-related cognitive impairment and ability to work, also published during the conduct of our study, Duijts et al. mentioned that the impact of cancer-related cognitive impairment on work-related outcomes in cancer survivors to date is not well-understood3. To better understand the impact, the authors stressed the importance of using a self-report instrument, such as the CSC-W DV, to measure cognitive functioning at work. Using a self-report instrument is important, as it takes into account the environment where a person is situated and interactions with the workplace and colleagues4. A better understanding of the impact of persistent physical and psychosocial problems on cancer patients at work may help to develop effective treatment strategies and more effective workplace interventions for cancer patients at work5.
Improvements in work functioning during 18 months after return to work
Measuring work functioning during a period of 18 months after return to work provides insight in the experienced difficulties in meeting the demands at work and in the course of these difficulties over time. Cancer patients showed improvements in their work functioning in the first 12 months after return to work. After this improvement, the average work functioning level was similar to the work functioning level in the general working population9. Work functioning remains stable in the period between 12 and 18 months. The improvements in work functioning are in line with the gradual return to work approach, whereby an occupational physician and a cancer patient in consultation decide how much work and what kind of work someone can do. However, work functioning did not improve in all cancer patients. Approximately, one-third of the cancer patients experienced persistently low work functioning after return to work.
One-third of the cancer patients need tailored guidance and support when back at work One-third of the cancer patients reported persistently low work functioning in the year following return to work. When returning to work, they experienced on average 34% of the time difficulties in meeting their job demands, which translates into 1.7 days of a full-time work/week. A year later, they experienced 28% of the time difficulties in meeting their job demands, which translates into 1.4 days of a full-time work/week. Although there was an improvement in work functioning in the year following return to work, the level was below the level of work functioning in the general population6. Cancer patients in this group might be at risk for negative work outcomes, such as (recurrent) sick leave or work disability, and therefore they might benefit from tailored guidance and support when resuming work. Hence, it is important to identify cancer patients who are at risk of low work functioning after return to work. Experiencing high levels of fatigue, depressive symptoms and most important, experiencing high levels of work-specific cognitive symptoms are characteristics of cancer patients who are at risk of low work functioning after return to work. Cancer patients who experienced less social support from colleagues were also at risk of low work functioning. Cancer type and cancer treatment were not associated with the level of work functioning. Two-thirds of the cancer patients reported high work functioning when back at work
Cancer patients who reported high work functioning experienced the highest increase in work functioning in the first 3 months after return to work. They reported similar levels of work functioning as workers in the general working population (which included about 30% of workers with a chronic disease)6. During the year following return to work, they experienced on average 7% of the time difficulties in meeting their job demands. This translates into 0.4 days of a full-time work/week. Cancer patients in this group often reported good to excellent health and a high quality of life. Furthermore, they had less time between diagnosis and return to work and perceived the moment of return to work more often as optimal, compared to cancer patients who experienced low work functioning after return to work.
Cancer type and cancer treatment less relevant for work functioning of cancer patients
Cancer patients with a particular cancer diagnosis or cancer treatment do not have a higher risk for low work functioning once they have resumed work. It seems that these clinical factors
are less important for managing the work functioning of cancer patients who returned to work. An explanation may be found in the period before returning to work. Previous research on predictors of return to work found that chemotherapy was negatively associated with return to work, while less invasive surgery was positively associated with return to work of cancer patients7. Cancer patients with a certain cancer type or cancer treatment that include extreme complaints were possibly not able to resume work. Furthermore, one-third of the cancer patients in our cohort returned to work during treatment. They do not have a higher risk for low work functioning once they have resumed work. In line with the Dutch Guideline Cancer and Work8, developed by the Netherlands Society of Occupational Medicine (NVAB), it is therefore argued that it seems not necessary to wait with returning to work until treatment completion, especially because work brings many positive effects for cancer patients, such as identity, income and social support9-11. Return to work should always be a personalized process, tailored to the needs of the cancer patient.
Work functioning mainly affected by psychosocial factors
The studies in this thesis showed that higher levels of fatigue, depressive symptoms and work-specific cognitive symptoms were associated with experiencing more difficulties with work functioning during the first 18 months after return to work. Fatigue, depressive symptoms and work-specific cognitive symptoms can persist for years after cancer diagnosis and cancer treatment, and do not only affect cancer patients not at work, but also those cancer patients at work1,12,13.
The mean fatigue and depressive symptom scores of the WOLICA sample were below the clinical cut-offs14 during the first 18 months after return to work. When investigating the course of fatigue and depressive symptoms, we found that both fatigue and depressive symptoms decreased during the first 18 months after return to work. On individual level, 32% of the cancer patients experienced severe fatigue after return to work, which decreased to 21% 18 months after return to work. For depressive symptoms, 10% of the cancer patients were classified with clinical depression after return to work, which decreased to 6% 18 months after return to work (data not published). The finding that health improves while working, suggests that it is not necessary to wait with returning to work until fully recovered.
One-third of the cancer patients need tailored guidance and support when back at work One-third of the cancer patients reported persistently low work functioning in the year following return to work. When returning to work, they experienced on average 34% of the time difficulties in meeting their job demands, which translates into 1.7 days of a full-time work/week. A year later, they experienced 28% of the time difficulties in meeting their job demands, which translates into 1.4 days of a full-time work/week. Although there was an improvement in work functioning in the year following return to work, the level was below the level of work functioning in the general population6. Cancer patients in this group might be at risk for negative work outcomes, such as (recurrent) sick leave or work disability, and therefore they might benefit from tailored guidance and support when resuming work. Hence, it is important to identify cancer patients who are at risk of low work functioning after return to work. Experiencing high levels of fatigue, depressive symptoms and most important, experiencing high levels of work-specific cognitive symptoms are characteristics of cancer patients who are at risk of low work functioning after return to work. Cancer patients who experienced less social support from colleagues were also at risk of low work functioning. Cancer type and cancer treatment were not associated with the level of work functioning. Two-thirds of the cancer patients reported high work functioning when back at work
Cancer patients who reported high work functioning experienced the highest increase in work functioning in the first 3 months after return to work. They reported similar levels of work functioning as workers in the general working population (which included about 30% of workers with a chronic disease)6. During the year following return to work, they experienced on average 7% of the time difficulties in meeting their job demands. This translates into 0.4 days of a full-time work/week. Cancer patients in this group often reported good to excellent health and a high quality of life. Furthermore, they had less time between diagnosis and return to work and perceived the moment of return to work more often as optimal, compared to cancer patients who experienced low work functioning after return to work.
Cancer type and cancer treatment less relevant for work functioning of cancer patients
Cancer patients with a particular cancer diagnosis or cancer treatment do not have a higher risk for low work functioning once they have resumed work. It seems that these clinical factors
are less important for managing the work functioning of cancer patients who returned to work. An explanation may be found in the period before returning to work. Previous research on predictors of return to work found that chemotherapy was negatively associated with return to work, while less invasive surgery was positively associated with return to work of cancer patients7. Cancer patients with a certain cancer type or cancer treatment that include extreme complaints were possibly not able to resume work. Furthermore, one-third of the cancer patients in our cohort returned to work during treatment. They do not have a higher risk for low work functioning once they have resumed work. In line with the Dutch Guideline Cancer and Work8, developed by the Netherlands Society of Occupational Medicine (NVAB), it is therefore argued that it seems not necessary to wait with returning to work until treatment completion, especially because work brings many positive effects for cancer patients, such as identity, income and social support9-11. Return to work should always be a personalized process, tailored to the needs of the cancer patient.
Work functioning mainly affected by psychosocial factors
The studies in this thesis showed that higher levels of fatigue, depressive symptoms and work-specific cognitive symptoms were associated with experiencing more difficulties with work functioning during the first 18 months after return to work. Fatigue, depressive symptoms and work-specific cognitive symptoms can persist for years after cancer diagnosis and cancer treatment, and do not only affect cancer patients not at work, but also those cancer patients at work1,12,13.
The mean fatigue and depressive symptom scores of the WOLICA sample were below the clinical cut-offs14 during the first 18 months after return to work. When investigating the course of fatigue and depressive symptoms, we found that both fatigue and depressive symptoms decreased during the first 18 months after return to work. On individual level, 32% of the cancer patients experienced severe fatigue after return to work, which decreased to 21% 18 months after return to work. For depressive symptoms, 10% of the cancer patients were classified with clinical depression after return to work, which decreased to 6% 18 months after return to work (data not published). The finding that health improves while working, suggests that it is not necessary to wait with returning to work until fully recovered.
Work-specific cognitive symptoms remain stable during 18 months after return to work and are associated with work functioning
The stable course of work-specific cognitive symptoms is in line with previous research among cancer patients on general cognitive symptoms, showing that cognitive symptoms persisted for years after cancer treatment15-17. As information about the level of work-specific cognitive symptoms experienced in the general working population is not available, it is difficult to interpret the impact of work-specific cognitive symptoms on cancer patients. Because the original CSC-W has a dichotomous response anchor (i.e. yes or no)18 and the Dutch Version has an ordinal five-point scale, it is also not possible to compare the outcomes of our sample with work-specific cognitive symptoms of cancer patients in the United States18 and China19. Higher levels of work-specific cognitive symptoms are associated with experiencing more difficulties with work functioning over time. This association can be interpreted in two ways, i.e. both as a between and a within person effect20. First, cancer patients with more
work-specific cognitive symptoms had lower work functioning scores compared to cancer patients with less work-specific cognitive symptoms. Second, an increase in work-specific cognitive symptoms within one cancer patient was associated with a decrease in work
functioning over time, indicating that an improvement in work-specific cognitive symptoms
may be beneficial for work functioning.
Cancer patients with non-manual jobs reported higher levels of work-specific cognitive symptoms over time compared to cancer patients with manual jobs. When using the International Standard Classification of Occupations (ISCO)21, cancer patients working, for example, as managers or (associate) professionals experienced more work-specific cognitive symptoms compared to cancer patients working, for example, as service and sales workers. An explanation might be that non-manual work is more cognitively demanding than manual work.
Continuing supervisor social support and working more hours per week are associated with better work functioning
Cancer patients experienced a decline in supervisor and colleague social support when back at work. This may be a natural workplace process once the disease is moving more and more to the background. However, the observed decrease in workplace social support, in particular the support of the supervisor, might negatively affect cancer patients’ work functioning over
time. Social support can help reducing the impact of a disease on work capacity22. Previously, social support was found to be an important factor for return to work of cancer patients23-25. This thesis shows that social support is also important for cancer patients’ work functioning after return to work. Therefore, continuing supervisor social support over a longer period is recommended.
Cancer patients reported an increase in working hours during the first 6 months after return to work. Their working hours remained stable during 6 to 18 months after return to work. The majority of the cancer patients (79%) were back at their contracted working hours 18 months after return to work. Those cancer patients who were not back at their contracted working hours worked on average 48% of their contracted working hours at 18 months after return to work (data not published). We further observed that working more hours per week was associated with higher levels of work functioning. A possible explanation for this relationship can be found in the gradual return to work approach. Even though we have not specifically examined whether an increase in working hours and work functioning is preceded by an improvement in health status, it is possible that cancer patients with less physical or psychosocial problems can work more hours per week, illustrated by experiencing less difficulties at work. Moreover, improvements in physical or psychosocial problems may lead to an increase in working hours and at the same time, better work functioning.
Methodological considerations
In this section, we address and discuss methodological issues concerning the design, the sample, the quality of the obtained data, and the degree to which our study supports inferences on causality.
Design
The studies in this thesis used quantitative data from the 18 months longitudinal WOrk Life After CAncer (WOLICA) cohort (n=384). The likelihood of information bias, i.e. systematic error in the obtained information26, was limited by the use of repeated measures. The WOLICA study did not have a control group with non-cancer patients. Consequently, it was not possible to compare work functioning scores to matched controls. Abma et al. conducted a comparison
Work-specific cognitive symptoms remain stable during 18 months after return to work and are associated with work functioning
The stable course of work-specific cognitive symptoms is in line with previous research among cancer patients on general cognitive symptoms, showing that cognitive symptoms persisted for years after cancer treatment15-17. As information about the level of work-specific cognitive symptoms experienced in the general working population is not available, it is difficult to interpret the impact of work-specific cognitive symptoms on cancer patients. Because the original CSC-W has a dichotomous response anchor (i.e. yes or no)18 and the Dutch Version has an ordinal five-point scale, it is also not possible to compare the outcomes of our sample with work-specific cognitive symptoms of cancer patients in the United States18 and China19. Higher levels of work-specific cognitive symptoms are associated with experiencing more difficulties with work functioning over time. This association can be interpreted in two ways, i.e. both as a between and a within person effect20. First, cancer patients with more
work-specific cognitive symptoms had lower work functioning scores compared to cancer patients with less work-specific cognitive symptoms. Second, an increase in work-specific cognitive symptoms within one cancer patient was associated with a decrease in work
functioning over time, indicating that an improvement in work-specific cognitive symptoms
may be beneficial for work functioning.
Cancer patients with non-manual jobs reported higher levels of work-specific cognitive symptoms over time compared to cancer patients with manual jobs. When using the International Standard Classification of Occupations (ISCO)21, cancer patients working, for example, as managers or (associate) professionals experienced more work-specific cognitive symptoms compared to cancer patients working, for example, as service and sales workers. An explanation might be that non-manual work is more cognitively demanding than manual work.
Continuing supervisor social support and working more hours per week are associated with better work functioning
Cancer patients experienced a decline in supervisor and colleague social support when back at work. This may be a natural workplace process once the disease is moving more and more to the background. However, the observed decrease in workplace social support, in particular the support of the supervisor, might negatively affect cancer patients’ work functioning over
time. Social support can help reducing the impact of a disease on work capacity22. Previously, social support was found to be an important factor for return to work of cancer patients23-25. This thesis shows that social support is also important for cancer patients’ work functioning after return to work. Therefore, continuing supervisor social support over a longer period is recommended.
Cancer patients reported an increase in working hours during the first 6 months after return to work. Their working hours remained stable during 6 to 18 months after return to work. The majority of the cancer patients (79%) were back at their contracted working hours 18 months after return to work. Those cancer patients who were not back at their contracted working hours worked on average 48% of their contracted working hours at 18 months after return to work (data not published). We further observed that working more hours per week was associated with higher levels of work functioning. A possible explanation for this relationship can be found in the gradual return to work approach. Even though we have not specifically examined whether an increase in working hours and work functioning is preceded by an improvement in health status, it is possible that cancer patients with less physical or psychosocial problems can work more hours per week, illustrated by experiencing less difficulties at work. Moreover, improvements in physical or psychosocial problems may lead to an increase in working hours and at the same time, better work functioning.
Methodological considerations
In this section, we address and discuss methodological issues concerning the design, the sample, the quality of the obtained data, and the degree to which our study supports inferences on causality.
Design
The studies in this thesis used quantitative data from the 18 months longitudinal WOrk Life After CAncer (WOLICA) cohort (n=384). The likelihood of information bias, i.e. systematic error in the obtained information26, was limited by the use of repeated measures. The WOLICA study did not have a control group with non-cancer patients. Consequently, it was not possible to compare work functioning scores to matched controls. Abma et al. conducted a comparison
study across workers from six different populations, including the general working population, and showed work functioning scores of these populations27. This information was used to interpret the results of cancer patients on work functioning. When comparing the work functioning scores of cancer patients during 18 months following diagnosis with the scores of the working population, the average work functioning levels were similar27.
Sample
For the focus group study and the longitudinal WOLICA cohort, the heterogeneous sample contained cancer patients with different cancer types and cancer treatments, which in both studies provided a comprehensive picture of work functioning after return to work. A large group of the cancer patients was diagnosed with breast cancer. This might be a disadvantage for study generalizability, but reflects the population of working cancer patients in the Netherlands, as breast cancer is one of the most common cancers in individuals of working age28. Approximately one-third of the cancer patients was still under treatment at the time of return to work. Even though this may have led to an underestimation of the level of work functioning and to an overestimation of cancer-related problems, our sample may be a good reflection of the population of working cancer patients shortly after their return to work.
It is important to note that cancer patients in the WOLICA cohort were mainly highly educated (39%) and medium educated (34%) – as is often seen in cancer studies. Moreover, cancer patients employed in manual work were underrepresented (12%). The results might therefore be difficult to generalize to workers with a lower educational level and to cancer patients in manual work. This has to be taken into account when interpreting the results, particularly with regard to the effects of work-related cognitive symptoms, because working in a manual job sets other requirements than working in a non-manual job.
A possible source of selection bias may have been introduced by the recruitment strategy. Occupational physicians may have chosen to not ask cancer patients with many cancer-related problems to participate in the study. This may have led to an underrepresentation of participants with many cancer-related problems26, which might have resulted in an overestimation of the level of work functioning and an underestimation of both psychosocial problems and the effects of cancer type and cancer treatment. Due to the lack of information about cancer patients who were not asked to participate or were asked but not
willing to participate, we cannot firmly state if the study sample is representative of patients who resumed work after cancer diagnosis and treatment.
Quality of obtained data
To measure the level of work functioning and work-specific cognitive symptoms, we used self-reported data, obtained from reliable and valid questionnaires. With repeated measures, we examined these outcomes over time. As measure for the level of work-specific cognitive symptoms, we did not use neuropsychological tests, which are considered to be the gold standard to assess cognitive performance of cancer patients independent of the context17,29. Because we were interested in cognitive performance in a specific context, namely cognitive symptoms experienced at the workplace, we used a self-reported measure, which takes into account the specific context. The Cognitive Symptom Checklist-Work (CSC-W21) was cross-culturally translated, adapted and validated and contains questions specific to a person’s work tasks18.
Implications for practice
Occupational physicians should assess work functioning as soon as possible when cancer patients are back at work. Cancer patients with high work functioning after return to work are likely to stay high on work functioning and guidance and support should focus on monitoring over time. In contrast, cancer patients with low work functioning after return to work are likely to stay low during the first 18 months after return to work and may need additional guidance and support in the post-return to work phase. For cancer patients with a low level of work functioning, occupational physicians should focus on reducing fatigue, depressive symptoms and work-specific cognitive symptoms, to improve work functioning. As fatigue and depressive symptoms are likely to contribute to cognitive symptoms30,31, they need to be jointly addressed. Interventions are not only important at the moment of return to work but also later, as improvements during the first 18 months after return to work might have a positive influence on work functioning. Occupational physicians and supervisors should be aware that
study across workers from six different populations, including the general working population, and showed work functioning scores of these populations27. This information was used to interpret the results of cancer patients on work functioning. When comparing the work functioning scores of cancer patients during 18 months following diagnosis with the scores of the working population, the average work functioning levels were similar27.
Sample
For the focus group study and the longitudinal WOLICA cohort, the heterogeneous sample contained cancer patients with different cancer types and cancer treatments, which in both studies provided a comprehensive picture of work functioning after return to work. A large group of the cancer patients was diagnosed with breast cancer. This might be a disadvantage for study generalizability, but reflects the population of working cancer patients in the Netherlands, as breast cancer is one of the most common cancers in individuals of working age28. Approximately one-third of the cancer patients was still under treatment at the time of return to work. Even though this may have led to an underestimation of the level of work functioning and to an overestimation of cancer-related problems, our sample may be a good reflection of the population of working cancer patients shortly after their return to work.
It is important to note that cancer patients in the WOLICA cohort were mainly highly educated (39%) and medium educated (34%) – as is often seen in cancer studies. Moreover, cancer patients employed in manual work were underrepresented (12%). The results might therefore be difficult to generalize to workers with a lower educational level and to cancer patients in manual work. This has to be taken into account when interpreting the results, particularly with regard to the effects of work-related cognitive symptoms, because working in a manual job sets other requirements than working in a non-manual job.
A possible source of selection bias may have been introduced by the recruitment strategy. Occupational physicians may have chosen to not ask cancer patients with many cancer-related problems to participate in the study. This may have led to an underrepresentation of participants with many cancer-related problems26, which might have resulted in an overestimation of the level of work functioning and an underestimation of both psychosocial problems and the effects of cancer type and cancer treatment. Due to the lack of information about cancer patients who were not asked to participate or were asked but not
willing to participate, we cannot firmly state if the study sample is representative of patients who resumed work after cancer diagnosis and treatment.
Quality of obtained data
To measure the level of work functioning and work-specific cognitive symptoms, we used self-reported data, obtained from reliable and valid questionnaires. With repeated measures, we examined these outcomes over time. As measure for the level of work-specific cognitive symptoms, we did not use neuropsychological tests, which are considered to be the gold standard to assess cognitive performance of cancer patients independent of the context17,29. Because we were interested in cognitive performance in a specific context, namely cognitive symptoms experienced at the workplace, we used a self-reported measure, which takes into account the specific context. The Cognitive Symptom Checklist-Work (CSC-W21) was cross-culturally translated, adapted and validated and contains questions specific to a person’s work tasks18.
Implications for practice
Occupational physicians should assess work functioning as soon as possible when cancer patients are back at work. Cancer patients with high work functioning after return to work are likely to stay high on work functioning and guidance and support should focus on monitoring over time. In contrast, cancer patients with low work functioning after return to work are likely to stay low during the first 18 months after return to work and may need additional guidance and support in the post-return to work phase. For cancer patients with a low level of work functioning, occupational physicians should focus on reducing fatigue, depressive symptoms and work-specific cognitive symptoms, to improve work functioning. As fatigue and depressive symptoms are likely to contribute to cognitive symptoms30,31, they need to be jointly addressed. Interventions are not only important at the moment of return to work but also later, as improvements during the first 18 months after return to work might have a positive influence on work functioning. Occupational physicians and supervisors should be aware that
cancer patients with non-manual jobs report more cognitive symptoms and should receive specific attention.
Supervisors and (occupational) physicians should be informed about the importance of continuous supervisor social support over time. Even though a decrease in social support may not be experienced as a problem by all cancer patients, clear communication between the supervisor, (occupational) physician and the cancer patient about support is recommended.
Medical specialists (i.e. general practitioners, oncologists, nurses) and occupational physicians should understand the relevance of continuing work - if possible - throughout cancer treatment. In the WOLICA cohort, cancer patients who returned to work during treatment reported similar levels of work functioning and work-specific cognitive symptoms over time as cancer patients who resumed work after treatment completion. The finding that health improves while working, suggests that it is not necessary to wait with returning to work until fully recovered. It is therefore argued that work may be resumed once the cancer patient is physically and mentally able to work and when guided and supported by the occupational physician. Moreover, medical specialists and occupational physicians should raise the cancer patients’ awareness for the positive effects of work in an early stage after diagnosis. The psychological benefits (e.g. identify, fairness)10 and practical benefits (e.g. income, social support)11 of (continuing) work for cancer patients should be discussed, together with the disadvantages of being absent from work for a longer time, such as loss of self-confidence in how to cope with colleagues32. The findings are in line with the Dutch Guideline for Cancer and Work8, which recommends occupational physicians to guide cancer patients to continue work - if possible - throughout cancer treatment.
Future research
In the future, interventions to improve work functioning should be developed and evaluated. It is important to identify barriers of sustainable return to work and work functioning, for example in the medical setting (e.g. treatment during work time) and in the specific work situation (e.g. practical impossibilities to perform certain work tasks). To improve work
functioning, the focus should be on reducing cognitive symptoms, fatigue and depressive symptoms. As fatigue and depressive symptoms are likely to contribute to cognitive symptoms30,31, they need to be jointly addressed. Future research also needs to focus on the questions ‘When is work functioning successful?’ and ‘What are the conditions or prerequisites for work functioning to be sustainable for cancer patients in the future?’ To answer these questions, it might be interesting to integrate additional perspectives, for example from the cancer patient, supervisor and colleagues.
Studies with larger cancer patient cohorts are needed. First, including more cancer patients with particular diagnoses offers the opportunity to examine whether workers with specific cancer types need additional guidance and support after return to work. The current study included different cancer types, but due to the limited number of cases for most cancer types, it was not possible to examine the effect of cancer type on work functioning in more detail. Second, larger studies including lower educated cancer patients and cancer patients employed in manual work are needed, to examine the effects of work functioning and related psychosocial characteristics in these specific groups in more detail.
To improve sustainable return to work and work functioning of cancer patients, their work outcomes should be monitored from the moment they are diagnosed with cancer. To identify barriers and facilitators for sustainable return to work and work functioning, future research on work outcomes should therefore ideally start directly after workers have been diagnosed with cancer, during treatment and during the return to work process, until the time that they are back at work for a longer period.
To enhance the use of the work-specific cognitive symptom questionnaire in daily practice, future research should focus on 1) developing norm values for different populations, and 2) examining the ability to detect changes over time (e.g. responsiveness) and other psychometric properties. Information about norm values is currently lacking, which makes it difficult to interpret the level of work-specific cognitive functioning among cancer patients. The need for an instrument measuring work-specific cognitive symptoms is demonstrated by our study. As a consequence of our study, the Dutch Guideline Cancer and Work recommends to use the CSC-W when guiding cancer patients back to work11.
cancer patients with non-manual jobs report more cognitive symptoms and should receive specific attention.
Supervisors and (occupational) physicians should be informed about the importance of continuous supervisor social support over time. Even though a decrease in social support may not be experienced as a problem by all cancer patients, clear communication between the supervisor, (occupational) physician and the cancer patient about support is recommended.
Medical specialists (i.e. general practitioners, oncologists, nurses) and occupational physicians should understand the relevance of continuing work - if possible - throughout cancer treatment. In the WOLICA cohort, cancer patients who returned to work during treatment reported similar levels of work functioning and work-specific cognitive symptoms over time as cancer patients who resumed work after treatment completion. The finding that health improves while working, suggests that it is not necessary to wait with returning to work until fully recovered. It is therefore argued that work may be resumed once the cancer patient is physically and mentally able to work and when guided and supported by the occupational physician. Moreover, medical specialists and occupational physicians should raise the cancer patients’ awareness for the positive effects of work in an early stage after diagnosis. The psychological benefits (e.g. identify, fairness)10 and practical benefits (e.g. income, social support)11 of (continuing) work for cancer patients should be discussed, together with the disadvantages of being absent from work for a longer time, such as loss of self-confidence in how to cope with colleagues32. The findings are in line with the Dutch Guideline for Cancer and Work8, which recommends occupational physicians to guide cancer patients to continue work - if possible - throughout cancer treatment.
Future research
In the future, interventions to improve work functioning should be developed and evaluated. It is important to identify barriers of sustainable return to work and work functioning, for example in the medical setting (e.g. treatment during work time) and in the specific work situation (e.g. practical impossibilities to perform certain work tasks). To improve work
functioning, the focus should be on reducing cognitive symptoms, fatigue and depressive symptoms. As fatigue and depressive symptoms are likely to contribute to cognitive symptoms30,31, they need to be jointly addressed. Future research also needs to focus on the questions ‘When is work functioning successful?’ and ‘What are the conditions or prerequisites for work functioning to be sustainable for cancer patients in the future?’ To answer these questions, it might be interesting to integrate additional perspectives, for example from the cancer patient, supervisor and colleagues.
Studies with larger cancer patient cohorts are needed. First, including more cancer patients with particular diagnoses offers the opportunity to examine whether workers with specific cancer types need additional guidance and support after return to work. The current study included different cancer types, but due to the limited number of cases for most cancer types, it was not possible to examine the effect of cancer type on work functioning in more detail. Second, larger studies including lower educated cancer patients and cancer patients employed in manual work are needed, to examine the effects of work functioning and related psychosocial characteristics in these specific groups in more detail.
To improve sustainable return to work and work functioning of cancer patients, their work outcomes should be monitored from the moment they are diagnosed with cancer. To identify barriers and facilitators for sustainable return to work and work functioning, future research on work outcomes should therefore ideally start directly after workers have been diagnosed with cancer, during treatment and during the return to work process, until the time that they are back at work for a longer period.
To enhance the use of the work-specific cognitive symptom questionnaire in daily practice, future research should focus on 1) developing norm values for different populations, and 2) examining the ability to detect changes over time (e.g. responsiveness) and other psychometric properties. Information about norm values is currently lacking, which makes it difficult to interpret the level of work-specific cognitive functioning among cancer patients. The need for an instrument measuring work-specific cognitive symptoms is demonstrated by our study. As a consequence of our study, the Dutch Guideline Cancer and Work recommends to use the CSC-W when guiding cancer patients back to work11.
Conclusion
Measuring work functioning and work-specific cognitive symptoms fills a knowledge gap in cancer and work research. We found improvements in work functioning during 18 months after return to work, but work functioning did not improve in all cancer patients. One-third of the cancer patients experienced persistently low work functioning after return to work, mainly due to high levels of fatigue, depressive symptoms and most important, high work-specific cognitive symptoms. As cancer patients with low work functioning after return to work are likely to stay low on work functioning during the first 18 months after return to work, they need additional guidance and support in the post-return to work phase. We recommend focusing on reducing fatigue, depressive symptoms and work-specific cognitive symptoms, in order to improve work functioning. As fatigue and depressive symptoms are likely to contribute to cognitive symptoms, these factors need to addressed comprehensively. To better interpret the level of work-specific cognitive functioning among cancer patients, norm values should be determined.
As work functioning and health outcomes improve after returning to work, cancer should be encouraged to resume work once they are physically and mentally able to work and when guided and supported by the occupational physician.
References
1. Duijts SFA, van Egmond MP, Spelten E, et al. Physical and psychosocial problems in cancer survivors beyond return to work: A systematic review. Psychooncology 2014;23:481-492. 2. Duijts SFA, Kieffer JM, van Muijen P, et al. Sustained employability and health-related quality
of life in cancer survivors up to four years after diagnosis. Acta Oncol 2017;56:174-182. 3. Duijts SFA, van der Beek AJ, Boelhouwer IG, et al. Cancer-related cognitive impairment and
patients' ability to work: A current perspective. Curr Opin Support Palliat Care 2017;11:19-23. 4. Munir F, Kalawsky K, Lawrence C, et al. Cognitive intervention for breast cancer patients
undergoing adjuvant chemotherapy: A needs analysis. Cancer Nurs 2011;34:385-392. 5. Hansen JA, Feuerstein M, Calvio LC, et al. Breast cancer survivors at work. J Occup Environ Med
2008;50:777-784.
6. Abma FI, van der Klink JJL, Bültmann U. The work role functioning questionnaire 2.0 (dutch version): Examination of its reliability, validity and responsiveness in the general working population. J Occup Rehabil 2013;23:135-147.
7. van Muijen P, Weevers NLEC, Snels IAK, et al. Predictors of return to work and employment in cancer survivors: A systematic review. Eur J Cancer Care (Engl) 2013;22:144-160.
8. Netherlands Society of Occupational Medicine (NVAB). Guideline cancer and work (Richtlijn kanker en werk; voor het handelen van de bedrijfsarts bij het behoud van en terugkeer naar werk). 2017, Utrecht.
9. Rasmussen DM, Elverdam B. The meaning of work and working life after cancer: An interview study. Psychooncology 2008;17:1232-1238.
10. Peteet JR. Cancer and the meaning of work. Gen Hosp Psychiatry 2000;22:200-205. 11. Hoffman B. Cancer survivors at work: A generation of progress. CA 2005;55:271-280. 12. Gandubert C, Carrière I, Escot C, et al. Onset and relapse of psychiatric disorders following
early breast cancer: A case-control study. Psychooncology 2009;18:1029-1037.
13. Deimling GT, Bowman KF, Sterns S, et al. Cancer-related health worries and psychological distress among older adult, long-term cancer survivors. Psychooncology 2006;15:306-320. 14. Manea L, Gilbody S, McMillan D. A diagnostic meta-analysis of the patient health
questionnaire-9 (PHQ-9) algorithm scoring method as a screen for depression. Gen Hosp
Psychiatry 2015;37:67-75.
15. Harrington C, Hansen J, Moskowitz M, et al. It's not over when it's over: Long-term symptoms in cancer Survivors—A systematic review. Int J Psychiatry Med 2010;40:163-181.
Conclusion
Measuring work functioning and work-specific cognitive symptoms fills a knowledge gap in cancer and work research. We found improvements in work functioning during 18 months after return to work, but work functioning did not improve in all cancer patients. One-third of the cancer patients experienced persistently low work functioning after return to work, mainly due to high levels of fatigue, depressive symptoms and most important, high work-specific cognitive symptoms. As cancer patients with low work functioning after return to work are likely to stay low on work functioning during the first 18 months after return to work, they need additional guidance and support in the post-return to work phase. We recommend focusing on reducing fatigue, depressive symptoms and work-specific cognitive symptoms, in order to improve work functioning. As fatigue and depressive symptoms are likely to contribute to cognitive symptoms, these factors need to addressed comprehensively. To better interpret the level of work-specific cognitive functioning among cancer patients, norm values should be determined.
As work functioning and health outcomes improve after returning to work, cancer should be encouraged to resume work once they are physically and mentally able to work and when guided and supported by the occupational physician.
References
1. Duijts SFA, van Egmond MP, Spelten E, et al. Physical and psychosocial problems in cancer survivors beyond return to work: A systematic review. Psychooncology 2014;23:481-492. 2. Duijts SFA, Kieffer JM, van Muijen P, et al. Sustained employability and health-related quality
of life in cancer survivors up to four years after diagnosis. Acta Oncol 2017;56:174-182. 3. Duijts SFA, van der Beek AJ, Boelhouwer IG, et al. Cancer-related cognitive impairment and
patients' ability to work: A current perspective. Curr Opin Support Palliat Care 2017;11:19-23. 4. Munir F, Kalawsky K, Lawrence C, et al. Cognitive intervention for breast cancer patients
undergoing adjuvant chemotherapy: A needs analysis. Cancer Nurs 2011;34:385-392. 5. Hansen JA, Feuerstein M, Calvio LC, et al. Breast cancer survivors at work. J Occup Environ Med
2008;50:777-784.
6. Abma FI, van der Klink JJL, Bültmann U. The work role functioning questionnaire 2.0 (dutch version): Examination of its reliability, validity and responsiveness in the general working population. J Occup Rehabil 2013;23:135-147.
7. van Muijen P, Weevers NLEC, Snels IAK, et al. Predictors of return to work and employment in cancer survivors: A systematic review. Eur J Cancer Care (Engl) 2013;22:144-160.
8. Netherlands Society of Occupational Medicine (NVAB). Guideline cancer and work (Richtlijn kanker en werk; voor het handelen van de bedrijfsarts bij het behoud van en terugkeer naar werk). 2017, Utrecht.
9. Rasmussen DM, Elverdam B. The meaning of work and working life after cancer: An interview study. Psychooncology 2008;17:1232-1238.
10. Peteet JR. Cancer and the meaning of work. Gen Hosp Psychiatry 2000;22:200-205. 11. Hoffman B. Cancer survivors at work: A generation of progress. CA 2005;55:271-280. 12. Gandubert C, Carrière I, Escot C, et al. Onset and relapse of psychiatric disorders following
early breast cancer: A case-control study. Psychooncology 2009;18:1029-1037.
13. Deimling GT, Bowman KF, Sterns S, et al. Cancer-related health worries and psychological distress among older adult, long-term cancer survivors. Psychooncology 2006;15:306-320. 14. Manea L, Gilbody S, McMillan D. A diagnostic meta-analysis of the patient health
questionnaire-9 (PHQ-9) algorithm scoring method as a screen for depression. Gen Hosp
Psychiatry 2015;37:67-75.
15. Harrington C, Hansen J, Moskowitz M, et al. It's not over when it's over: Long-term symptoms in cancer Survivors—A systematic review. Int J Psychiatry Med 2010;40:163-181.
16. Koppelmans V, Breteler MMB, Boogerd W, et al. Neuropsychological performance in survivors of breast cancer more than 20 years after adjuvant chemotherapy. J Clin Oncol 2012;30:1080-1086.
17. Denlinger CS, Ligibel JA, Are M, et al. Survivorship: Cognitive function, version 1.2014. J Natl
Compr Canc Netw 2014;12:976-986.
18. Ottati A, Feuerstein M. Brief self-report measure of work-related cognitive limitations in breast cancer survivors. J Cancer Surviv 2013;7:262-273.
19. Cheng ASK, Zeng Y, Feuerstein M. Validation of the Chinese version of the cognitive symptom checklist-work-21 in breast cancer survivors. J Occup Rehabil 2015;25:685-695.
20. Twisk JWR. Applied longitudinal data analysis for epidemiology, a practical guide. New York, NY: Cambridge University Press 2003.
21. Hoffmann E. International statistical comparisons of occupational and social structures problems, possibilities and the role of ISCO-88. In: Hoffmeyer-Zlotnik, ed. Advances in cross-national comparisons. New York: Kluwer Academic/Plenum Publishers, 2003. 137-158. 22. Nilsson MI, Petersson L, Wennman-Larsen A, et al. Adjustment and social support at work early
after breast cancer surgery and its associations with sickness absence. Psychooncology 2013;22:2755-2762.
23. Banning M. Employment and breast cancer: A meta-ethnography. Eur J Cancer Care (Engl) 2011;20:708-719.
24. Johnsson A, Fornander T, Rutqvist LE, et al. Factors influencing return to work: A narrative study of women treated for breast cancer. Eur J Cancer Care (Engl) 2010;19:317-323. 25. Wells M, Williams B, Firnigl D, et al. Supporting 'work-related goals' rather than 'return to work'
after cancer? A systematic review and meta-synthesis of 25 qualitative studies.
Psychooncology 2013;22:1208-1219.
26. Rothman K. Epidemiology: An introduction. Oxford: Oxford University Press; 2012.
27. Abma FI, Bültmann U, Amick BC, et al. The Work Role Functioning Questionnaire v2.0 Showed Consistent Factor Structure Across Six Working Samples. J Occup Rehabil 2017. doi:
10.1007/s10926-017-9722-1.
28. Roelen CAM, Koopmans PC, Groothoff JW, et al. Return to work after cancer diagnosed in 2002, 2005 and 2008. J Occup Rehabil 2011;21:335-341.
29. Moore HCF. An overview of chemotherapy-related cognitive dysfunction, or 'chemobrain'.
Oncology (Williston Park) 2014;28:797-804.
30. Hurria A, Somlo G, Ahles T. Renaming "chemobrain". Cancer Invest 2007;25:373-377. 31. Valentine AD, Meyers CA. Cognitive and mood disturbance as causes and symptoms of fatigue
in cancer patients. Cancer 2001;92:1694-1698.
32. Knott V, Zrim S, Shanahan E, et al. Returning to work following curative chemotherapy: A qualitative study of return to work barriers and preferences for intervention. Supportive Care
16. Koppelmans V, Breteler MMB, Boogerd W, et al. Neuropsychological performance in survivors of breast cancer more than 20 years after adjuvant chemotherapy. J Clin Oncol 2012;30:1080-1086.
17. Denlinger CS, Ligibel JA, Are M, et al. Survivorship: Cognitive function, version 1.2014. J Natl
Compr Canc Netw 2014;12:976-986.
18. Ottati A, Feuerstein M. Brief self-report measure of work-related cognitive limitations in breast cancer survivors. J Cancer Surviv 2013;7:262-273.
19. Cheng ASK, Zeng Y, Feuerstein M. Validation of the Chinese version of the cognitive symptom checklist-work-21 in breast cancer survivors. J Occup Rehabil 2015;25:685-695.
20. Twisk JWR. Applied longitudinal data analysis for epidemiology, a practical guide. New York, NY: Cambridge University Press 2003.
21. Hoffmann E. International statistical comparisons of occupational and social structures problems, possibilities and the role of ISCO-88. In: Hoffmeyer-Zlotnik, ed. Advances in cross-national comparisons. New York: Kluwer Academic/Plenum Publishers, 2003. 137-158. 22. Nilsson MI, Petersson L, Wennman-Larsen A, et al. Adjustment and social support at work early
after breast cancer surgery and its associations with sickness absence. Psychooncology 2013;22:2755-2762.
23. Banning M. Employment and breast cancer: A meta-ethnography. Eur J Cancer Care (Engl) 2011;20:708-719.
24. Johnsson A, Fornander T, Rutqvist LE, et al. Factors influencing return to work: A narrative study of women treated for breast cancer. Eur J Cancer Care (Engl) 2010;19:317-323. 25. Wells M, Williams B, Firnigl D, et al. Supporting 'work-related goals' rather than 'return to work'
after cancer? A systematic review and meta-synthesis of 25 qualitative studies.
Psychooncology 2013;22:1208-1219.
26. Rothman K. Epidemiology: An introduction. Oxford: Oxford University Press; 2012.
27. Abma FI, Bültmann U, Amick BC, et al. The Work Role Functioning Questionnaire v2.0 Showed Consistent Factor Structure Across Six Working Samples. J Occup Rehabil 2017. doi:
10.1007/s10926-017-9722-1.
28. Roelen CAM, Koopmans PC, Groothoff JW, et al. Return to work after cancer diagnosed in 2002, 2005 and 2008. J Occup Rehabil 2011;21:335-341.
29. Moore HCF. An overview of chemotherapy-related cognitive dysfunction, or 'chemobrain'.
Oncology (Williston Park) 2014;28:797-804.
30. Hurria A, Somlo G, Ahles T. Renaming "chemobrain". Cancer Invest 2007;25:373-377. 31. Valentine AD, Meyers CA. Cognitive and mood disturbance as causes and symptoms of fatigue
in cancer patients. Cancer 2001;92:1694-1698.
32. Knott V, Zrim S, Shanahan E, et al. Returning to work following curative chemotherapy: A qualitative study of return to work barriers and preferences for intervention. Supportive Care
