Neoadjuvant endocrine therapy for strongly hormone receptor-positive and HER2-negative early breast cancer: results of a prospective multi-center study.

PURPOSE: For estrogen receptor (ER)-positive breast cancer, neoadjuvant endocrine therapy (NET) has been shown to be as effective as neoadjuvant chemotherapy (NACT). We evaluated the prognostic significance of Preoperative Endocrine Prognostic Index (PEPI). METHODS: We conducted a prospective, multi-center, non-randomized, controlled trial that enrolled postmenopausal early-stage strongly ER-positive (≥ 50%) and HER2-negative breast cancer patients. All patients were given 4-month NET before surgery. The primary objective was to investigate the 5-year recurrence-free survival (RFS) in patients who had PEPI 0-1 or pathological complete response (pCR) without chemotherapy. Patients who had PEPI 0-1 or pCR were recommended to receive adjuvant endocrine therapy only and patients had PEPI ≥ 2 may receive adjuvant chemotherapy at the discretion of the treating physician. RESULTS: A total of 410 patients were included and 352 patients constituted the per-protocol population. Overall, 9 patients (2.5%) had pCR (ypT0/is ypN0), 128 patients (36.4%) had PEPI = 0, and 56 patients (15.9%) had PEPI = 1. After a median follow-up of 60 months (4-104 months), patients who had PEPI 0-1 or pCR showed an improved 5-year RFS [99.5% (95% CI 98.5-99.9%) for PEPI 0-1 or pCR group vs. 93.7% (95% CI 89.6-97.8%) for PEPI ≥ 2 group, P = 0.028]. No survival difference was detected between patients received adjuvant chemotherapy vs. no chemotherapy among PEPI ≥ 2 cases. CONCLUSION: PEPI 0-1 or pCR may be used to define a group of ER-positive and HER2-negative postmenopausal early breast cancer patients with low relapse risk for whom adjuvant chemotherapy can be safely withheld. Studies on the identification and alternative treatment options for endocrine-resistant tumors are warranted. CLINICAL TRIAL REGISTRATION: NCT01613560.