Villarreal-Garza C, Mesa-Chavez F, Ferrigno AS, et al. - This cross-sectional study compared the endocrine therapy (ET) prescribed to premenopausal breast cancer patients with the definite treatment taken by patients in order to characterize compliance behaviors and detect areas that may be targeted to promote optimal adherence. Three Mexican referral centers identified premenopausal women with stage I-III hormone-sensitive breast cancer who had received adjuvant ET in the previous 1–5 years. One hundred thirty-two (71%) of the 186 patients who met the inclusion criteria agreed to participate and were analyzed. Premenopausal Mexican women self-report astonishingly high rates of adequate ET adherence. However, a considerable proportion misses ≥1 doses/month, usually due to forgetfulness. Notably, due to suboptimal prescription of ovarian function suppression (OFS), only 64% receive standard-of-care ET. Interventions that remind patients to take their ET, improve physicians' knowledge of the importance of OFS in high-risk patients, and expand access to OFS could be critical to improving optimal ET implementation and adherence, which could lead to improved patient outcomes.