Wulaningsih W, et al. - Researchers investigated issues related to non-adherence to endocrine treatment, including the possible influence of comorbidity burden and medical conditions. Participants were 4,645 women who had at least one dispensation of tamoxifen or aromatase inhibitors (AIs) for stage I–III, ER-positive breast cancer and 5 years of follow-up with no distant recurrence. In this study, 21% of women became non-adherent. The factors that were found to be related to non-adherence included greater comorbidity burden during follow-up, pre-diagnostic hormone replacement therapy use, not being married, high educational level, and use of symptom-relieving drugs. Lower odds of non-adherence were noted in relation to HER-2 positivity and adjuvant chemotherapy. For the presence of lymph node metastasis, higher tumor grade, and use of AIs vs tamoxifen, similar patterns were observed. In women with increasing Charlson comorbidity index (CCI), myocardial infarction and chronic pulmonary disease were mainly related to non-adherence.