In total, 998 studies were identified from the systematic search and three additional relevant studies were found in the manual reference list search of included articles. After removing duplicates, and exclusion based on title and abstract, 41 full-text articles were retrieved for full-text screening. Of these, 21 studies were excluded because they did not meet the selection criteria (Fig. 1). An overview of the main characteristics of the remaining 20 studies and their findings is provided in Tables 1 and 2. In short, 11 studies had a quantitative design [25,26,27,28,29,30,31,32,33,34,35] and nine had a qualitative design [7, 36,37,38,39,40,41,42,43]. The majority of the studies was conducted in the United States (n = 7) [26, 27, 30, 33, 36, 38, 43] and Europe (Netherlands, n = 3 [25, 37, 41]; United Kingdom, n = 3 [7, 28, 39]; Sweden, n = 3 [31, 32, 40]; joint cohort Nordic countries, n = 1 ), two studies were conducted in Canada [34, 35] and one in Malaysia . Seven studies were of prospective nature, with follow-up periods ranging from 3 months to 4 years [25, 28, 31,32,33,34] and 13 studies had a cross-sectional design [7, 26, 27, 29, 30, 35,36,37,38,39,40,41,42,43]. One study was reported in two articles, with the first comprising the baseline results  and the other reporting the findings at long-term follow-up . Four studies reported on short-term outcomes, occurring in the first year after breast cancer diagnosis [28, 31, 35, 40], while 14 studies reported on long-term outcomes [7, 25,26,27, 29, 30, 32,33,34, 36, 38, 39, 41, 43]. Two qualitative studies did not clearly define how much time had elapsed between breast cancer diagnosis and the problems participants disclosed [37, 42]. Study sample sizes ranged from n = 44 to n = 1111 breast cancer survivors in the quantitative studies and from n = 10 to n = 74 survivors in the qualitative studies. None of the studies included male breast cancer survivors in their study sample. In two studies, the populations consisted of a mixed cancer group, in which seven out of ten participants (70%)  and 219 out of 431 participants (51%)  were treated for breast cancer. In only two studies, the results regarding the relation between impairment of functioning and work were compared to a control group [26, 30].
Overall, we agreed that the methodological quality of the studies was high. For 11 studies, all items in the quality assessment were scored positively [27,28,29,30,31,32, 34, 37, 40, 41, 43]. In the remaining articles reporting on quantitative studies there may have been confounding , some measurement bias , or there was a lack of clarity regarding participant sampling [26, 35]. In one article there was also insufficient discussion of potential bias, generalizability and the interpretation of the results . Concerns about articles reporting on qualitative studies were mainly related to adequately addressing ethical issues [7, 36, 38] and considering the relationship between researcher and participants [7, 38, 39, 42]. Furthermore, one of these articles also scored negatively on the appropriateness of the research design and the method of data analysis . Taking into consideration the assessed quality of the studies, we decided not to deploy a weight difference when describing the results.
A total of 11 studies reported quantitative results regarding one or more domains of functioning [25,26,27,28,29,30,31,32,33,34,35]. Three studies described general functioning [27, 28, 31], seven studies described physical functioning [25, 28, 29, 31, 33,34,35], six studies described cognitive functioning [26, 28,29,30,31, 33], two studies described social functioning in general [28, 31], and finally, three studies described emotional functioning in general [28, 31, 32]. These domains were evaluated by means of medical assessment [25, 34, 35], telephone interviews , neuropsychological performance tests , or questionnaires, such as the Cognitive Symptom Checklist [26, 30], Activity Level Scale , Work Ability Index (which covers physical and cognitive work ability) , Cognitive Stability Index , or EORTC QLQ-C30 [28, 32] and Breast Cancer-Specific Quality of Life Questionnaire (QLQ-BR23) [31, 32]. The domains of functioning were investigated in relation to work ability [26, 27, 29, 30, 34, 35], RTW [28, 31], duration until RTW [25, 28], employment status [29, 33], sickness absence [27, 32] and working hours .
General and Role Functioning
Functional status in general and role functioning were investigated in relation to various work-related outcomes. The findings indicated that better functional status was associated with less sickness absence, and higher work productivity . Better role functioning was associated with a slightly increased chance to RTW , but not with the duration until RTW .
Generally, problems with physical functioning were associated with negative work outcomes. For instance, a higher proportion of breast cancer survivors with physical disabilities was not employed or had left the workforce at 12 and 18 months after diagnosis . In addition, reduced physical work ability led to more than a twofold increase in work changes and less overall work ability . More specifically, problems with shoulder functioning were reported to impact RTW and work ability after RTW. For example, limited range of motion was associated with a loss of productivity , which was still apparent 2.5–3 years after surgery . Furthermore, shoulder functioning impairment prolonged sick leave duration until partial RTW, but not until full RTW . Interestingly, general physical functioning was not associated with duration until RTW  or working hours .
Cognitive functioning was evaluated by means of performance-based test [26, 31] and self-reported measures [26, 28,29,30, 33]. Breast cancer survivors with low scores on neuropsychological performance tests did not differ from those who had high scores with regard to RTW  and work output . Findings from self-reported measures were somewhat inconsistent. Breast cancer survivors with a higher level of subjective cognitive impairment were more likely to be unemployed, to have left the workforce , or have lower work output . However, other findings indicated that subjective cognitive functioning was not associated with work-related outcomes, such as duration until RTW , work productivity , working hours , and work changes .
Social and Emotional Functioning
Less commonly investigated in relation to work-related outcomes were the domains of social and emotional functioning. Better social functioning was associated with higher RTW rates , but not with the duration until RTW . With respect to emotional functioning, none of the findings showed significant associations with work-related outcomes in breast cancer survivors [28, 31, 32].
A total of nine studies reported qualitative results regarding one or more domains of functioning [7, 36,37,38,39,40,41,42,43]. One study described general functioning , three studies described physical functioning [38, 41, 42], seven studies described cognitive functioning [7, 36, 37, 39,40,41, 43], and seven studies described emotional functioning [7, 36, 37, 39, 40, 42, 43]. Study participants were asked about the various domains through interviews [7, 36, 37, 41, 43], focus group discussions [7, 36, 39, 40, 42] or a comment section in a survey . The domains of functioning were mainly described in relation to RTW [38,39,40,41,42], and work ability [7, 36, 37, 39, 40, 43].
Impaired functioning in general was described as the driver of decisions on going to work or taking sick leave immediately following diagnosis, during treatment and in the phase thereafter .
Problems with mobility and executing physical tasks, such as carrying and walking, were reported to hamper RTW [38, 41, 42]. This became clear from studies in which women related their physical impairments to specific tasks at work. For example, a participant in the study by Tan et al.  explained: “I am physically tired; I was not able to walk long distance, and not able to monitor work because I noticed I was breathless during walking or going up a flight of stair.” In some cases, the decision not to resume a job is made by others than the breast cancer survivor, which was explained by one woman in a study, in which women were interviewed who had undergone a mastectomy: “I was the assistant manager of a convenience store and did a lot of heavy lifting and stacking. They would not take me back after the surgery” .
The findings showed that work-related outcomes were greatly impacted by cognitive impairments, including problems with concentration, attention, memory, pace of thought, multitasking, executive functioning, speed of processing and decision-making. These impairments were perceived to be related to the process of returning to work [39, 41, 42], as well as to problems with work ability by occupationally active breast cancer survivors [7, 36, 37, 39, 40, 43]. Impairments in cognitive functioning commonly became apparent beyond RTW, as was explained by a 51-year old senior receptionist in a study on chemotherapy-induced cognitive problems: “It was when I went back to work I noticed, I felt as though I’d had a lobotomy” . Especially when numerous cognitive functions are required for completing a job task, this was described as leading to problems when working: “It makes my job a lot harder, because as a teacher you have to do everything all at once. So, when I leave at the end of the day, I am spent, when before I was energetic. And it’s not a physical spent; it is a mental spent that I didn’t used to have” . Fortunately, the negative impact of cognitive impairment was also reported to diminish as time passed by, which was discussed by women, who had undergone breast surgery, in a focus group study: “I had been on sick leave for a month when I realized that I could not concentrate, but now I work just as before” .
Breast cancer diagnosis and treatment were reported to affect emotional functioning, which influenced choices on RTW. For instance, returning to work was described as a source of stress, at times leading women to tear up [7, 37]. Furthermore, low-spiritedness, fears, worries, frustrations and insecurity about appearances made it challenging for some breast cancer survivors to resume employment [7, 40, 42]. One woman elaborated on her insecurity at work after getting a breast prosthesis: “I had to lean down to do anything on the bottom, lower shelf or even for bags to pack them, I was like this [covered her chest] all the time, holding it together… every minute of my working day you’re thinking of it” . Cognitive impairment resulting from treatment was frequently cited as an additional reason for insecurity and frustration [36, 39, 43]. These problems in turn were explained to change the experience of work as it used to be, which for instance made an office manager retire early: “With this memory thing, I was very frustrated at work and so I thought that I can’t go on like this. It was a chore now going to work than a joy. I just assessed the situation and said that it’s not worth it” .