Background Neoadjuvant endocrine therapy (NET) has been demonstrated to improve breast-conserving rate and is a widely accepted treatment option for postmenopausal patients with hormone receptor-positive breast cancer. There are few reports on the association of NET response and long-term outcomes. Objectives To investigate the prognostic value of clinical response to NET. Methods Long-term outcomes of NET were examined in 107 patients who participated in the multicentre prospective neoadjuvant exemestane study, JFMC34-0601. Patients were treated with 25 mg/day exemestane for 16 weeks followed by an 8-week extension depending on the treatment response. Results Clinical response included partial response (PR) in 58 patients, stable disease in 41 patients and progressive disease (PD) in 8 patients. Clinical response was significantly associated with disease-free survival (DFS), distant disease-free survival (DDFS) and overall survival (OS) (P<0.0001 for all). Especially, patients with PD showed markedly poor outcomes with median DFS=17.8 months (HR (vs PR): 7.7 (95% CI 1.6 to 33)) and median OS=37.7 months (HR (vs PR): 26.3 (95% CI 2.4 to 655)). Preoperative endocrine prognostic index (PEPI) were associated with DFS and marginally with OS (P=0.022 and 0.066, respectively). PEPI=0 indicated an excellent prognosis with 95% 5-year DFS (95% CI 73 to 99). In the multivariate analysis including T stage, nodal status and Ki67, clinical response was an independent prognostic factor for DFS, DDFS and OS (P=0.032, 0.0007 and 0.020, respectively), whereas PEPI was marginally associated with DFS and OS (P=0.079 and 0.068, respectively). Conclusions Clinical response to NET showed an independent prognostic value. Patients with PD had markedly poor prognosis, indicating a need of additional therapy. PEPI=0 indicated an excellent prognosis. The integration of clinical response and PEPI would improve decision-making with regard to treatment options for endocrine-responsive breast cancer when these results are validated in a larger clinical trial. Trial registration number UMIN C000000345.
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