BACKGROUND: Despite the questionable effectiveness of oral complementary and alternative medicine (OCAM) in relieving cancer-related symptoms, including fatigue (CRF), many patients use it aiming to improve their quality of life. We assessed factors associated with OCAM use, focusing on CRF. METHODS: Women with stage I-III breast cancer (BC) were included from CANTO (NCT01993498). OCAM use was defined as taking homeopathy, vitamins/minerals, or herbal/dietary supplements. Multivariable multinomial logistic regressions evaluated associations of CRF (EORTC QLQ-C30), patient, and treatment characteristics with OCAM use. RESULTS: Among 5237 women, 23.0% reported OCAM use overall (49.3% at diagnosis, 50.7% starting post-diagnosis), mostly homeopathy (65.4%). Mean (SD) CRF score was 27.6 (24.0) at diagnosis and 35.1 (25.3) at post-diagnosis. More intense CRF was consistently associated with OCAM use at diagnosis and post-diagnosis [adjusted odds ratio (aOR) for 10-point increase 1.05 (95% Confidence interval 1.01-1.09) and 1.04 (1.01-1.09) vs. never use, respectively]. Odds of using OCAM at diagnosis were higher among older [for 5-year increase, 1.09 (1.04-1.14)] and more educated patients [college vs. primary 1.80 (1.27-2.55)]. Women with income > 3000 [vs. < 1500 euros/month, 1.44 (1.02-2.03)], anxiety [vs. not, 1.25 (1.01-1.54)], and those receiving chemotherapy [vs. not, 1.32 (1.04-1.68)] had higher odds of using OCAM post-diagnosis. CONCLUSION: One-in-four patients reported use of OCAM. More severe CRF was consistently associated with its use. Moreover, older, better educated, wealthier, more anxious women, and those receiving chemotherapy seemed more prone to use OCAM. Characterizing profiles of BC patients more frequently resorting to OCAM may help deliver targeted information about its benefits and potential risks.< Réduire