Adjuvant S-1 plus endocrine therapy for ER-positive, HER2-negative, primary breast cancer: post-POTENT trial prognostic survey.

This multicenter observational study investigated the prognosis of patients who participated in the Phase III POTENT trial, which examined combining S-1 with standard endocrine therapy in patients with estrogen receptor-positive, HER2-negative early breast cancer, over a longer follow-up period. The primary endpoint was overall survival (OS), with invasive disease-free survival (IDFS) and distant disease-free survival (DDFS) as secondary endpoints. Of the 1,930 POTENT trial participants, 1,593 patients (790 for S-1 and 803 for endocrine therapy alone) were included here. The median follow-up time was 77.5 months. Fifty-one and 58 deaths were observed in the S-1 and endocrine therapy alone groups, respectively. The 6-year OS rates were similar, with 94.4% in the S-1 group and 93.1% in the endocrine therapy alone group. Overall, both endocrine therapy alone and endocrine therapy plus S-1 resulted in favorable OS. Combining S-1 with endocrine therapy maintained the previously observed benefits of IDFS and DDFS.