https://onlinelibrary.wiley.com/doi/abs/10.1002/pon.4740 PAPER Free Access Does stress increase risk of breast cancer? A 15‐year prospective study. Phyllis Butow Melanie Price Joseph Coll Katherine Tucker Bettina Meiser Roger Milne Judith Wilson Louise Heiniger Brandi Baylock Tracey Bullen Prue Weideman Abstract Objective The possible impact of stress on cancer incidence remains controversial. We prospectively evaluated associations between life event stressors, social support, personality characteristics (optimism, anger control, anti‐emotionality) and risk of developing primary breast cancer (BCa), in women at increased familial risk of BCa. Methods A prospective cohort, repeated measures design was employed. Recruitment was through the Kathleen Cuningham Foundation Consortium for Research into Familial breast cancer (kConFab), which collects genetic, epidemiological and clinical data from Australasian families with multiple BCa cases. Acute and chronic stressors for the prior three years, and psychosocial, clinical and epidemiological variables were measured at cohort entry and at three‐yearly intervals. Cox proportional hazards regression analysis controlling for BCa risk factors and familial clustering, was undertaken. The primary outcome was histopathologically confirmed BCa (invasive or ductal carcinoma in situ (DCIS), including occult cases diagnosed during risk‐reducing mastectomy). Results Of 3,595 consecutive women invited to participate, 3,054 (85.0%) consented. Of these, 2,739 (89.7%) from 990 families (range 1‐16 per family) completed at least one assessment point. During the study 103 women were diagnosed with BCa. No stressor or psychosocial variable or interaction between them, was significantly associated with BCa in unadjusted or adjusted models (total acute stressors HR=1·03 (0·99‐1·08), p=0·19; total chronic stressors HR=1·0 [0·90‐1·11], p=0·98). Conclusions This study did not demonstrate an association between acute and chronic stressors, social support, optimism, anti‐emotionality or anger control, and BCa risk. Women should focus on proven methods of BCa risk reduction.