Less necessity of adjuvant S‐1 treatment in non‐monarchE‐eligible patients

BACKGROUND: In monarchE and Postoperative Therapy with Endocrine and TS‐1 (POTENT) trials, abemaciclib and S‐1 have, respectively, shown to be effective as adjuvant therapies for luminal breast cancer (BC), although whether patients who meet the criteria are at high risk of recurrence compared to non‐eligible patients is still unknown. Here, we investigated recurrence risk according to the criteria of each trial in Japanese patients. METHODS: We reviewed the records of 992 patients who received surgery at Chiba University Hospital for stage I–III BC from January 2017 to May 2022 and selected 553 analytic cohort patients and retrospectively analyzed the relapse‐free survival of the patients as the primary endpoint. High‐recurrence risk was defined according to monarchE trial and POTENT trial. RESULTS: The 5‐year RFS for monarchE cohort 1 and cohort 2 eligible patients were 77.78% and 89.33%, respectively, which were significantly lower than monarchE non‐eligible patients (98.31%; p < 0.0001). However, the 5‐year RFS rate for POTENT eligible patients (90.51%) was lower than for POTENT non‐eligible patients (98.75%; p = 0.0001); excluding those who met the monarchE criteria, the prognosis of POTENT eligible patients had no significant differences from the prognosis of patients with POTENT non‐eligible BC (p = 0.3100). CONCLUSION: MonarchE criteria accurately identify patients who are prone to relapse. Moreover, although POTENT criteria also suggested a reasonable capacity for recurrence prediction, there was no significant difference in recurrence between POTENT non‐eligible patients and the patients who were POTENT but not monarchE eligible. This might offer justification for reconsidering the use of S‐1 in monarchE non‐eligible patients.