Delayed adjuvant endocrine therapy is associated with decreased recurrence-free survival following neoadjuvant chemotherapy for breast cancer

Background: In hormone receptor-positive breast cancer (HRPBC), endocrine therapy is often initiated after adjuvant radiotherapy given concerns of radiation fibrosis. No studies have investigated how this may impact outcomes in high-risk patients undergoing neoadjuvant chemotherapy (NAC). Methods: Females with nonmetastatic HRPBC receiving NAC from 2011 to 2017 were identified from our multi -institutional database. Interval from surgery to endocrine therapy (ISET) was calculated in weeks. Recurrence -free survival (RFS) and overall survival (OS) were evaluated with Kaplan-Meier and Cox proportional hazards modeling. Results: Of 280 patients, 179 (64%) received adjuvant radiotherapy; all deaths (n = 25) and 90% (n = 27) of recurrences occurred in this group, which was the focus of subsequent analysis. Median follow-up was 49 months. Recurrences were predominantly distant metastases (n = 21, 81%). Median ISET was 12 weeks (range 0-55 weeks). On multivariable analysis, ISET >14 weeks was independently associ-ated with worse RFS (HR 3.20, 95% C.I. 1.22-8.40, P = 0.02) but not OS (HR 2.15, 95% C.I. 0.75-6.15, P = 0.15). Conclusion: In patients with HRPBC treated with NAC and adjuvant radiation, increasing ISET is associated with adverse oncologic outcomes.