Background: The interplay between breast cancer (BC) late effects, psychosocial and work-related factors in return to work (RTW) is not well understood. Previous reports were retrospective and did not combine all these features. Methods: We used data of a French prospective cohort study (CANTO, NCT01993498) of stage I-III BC patients (pts) including detailed clinical data of 1,874 pts working at diagnosis (dx) and ≥5 years younger than legal retirement age. The outcome was non-RTW 2 years after dx. Multivariable regressions were conducted to identify correlates of non-RTW. First, we examined the independent effect of treatments, toxicities (Common Toxicity Criteria Adverse Events), and patient reported outcomes (EORTC BR23 and FA12; Hospital Anxiety and Depression Scale) collected shortly after end of primary treatment. Then, in a restricted sample of 1,003 pts with working conditions (WC) information available, we fitted models to account for detailed pre-dx WC including type of contract, working hours, strenuous postures, supportive environment, degree of autonomy and perception of work. All models were adjusted for age, stage, marital status, socioeconomic status and comorbidities. Results: Two years after dx, 21% of pts did not work. Adjusted odds of non-RTW were increased among pts treated with combinations of chemotherapy (CT) and trastuzumab (TR) (e.g. OR of CT-TR = 2.20 [95% CI 1.24-3.88] and OR of CT-TR-hormonotherapy (HT) = 1.72 [1.13-2.63] vs. treated only with CT-HT), who had severe arm morbidity (OR = 1.73 [1.27-2.36] vs. no), severe emotional fatigue (OR = 1.55 [1.03-2.32] vs. no), anxiety (OR = 1.51 [1.02-2.23] vs. no), or depression (OR = 2.23 [1.27-3.94] vs no). In addition, we also found that the odds of non-RTW were increased among pts who had shift working hours (OR = 2.23 [1.32-3.76] vs. no), who did not work in a supportive environment before dx (OR = 2.24 [1.44-3.50] vs. supportive) and who perceived their job as boring (OR = 3.57 [1.71-7.46] vs. not boring). Conclusions: More than 1/5 of pts did not RTW 2 years after dx, with treatment (trastuzumab), clinical, psychological and work-related factors being associated with job reintegration. Multidisciplinary strategies are needed to support BC survivors.