De-escalation of five years adjuvant endocrine therapy duration in patients with ER-low positive (immunohistochemical 1% to 10%) early-stage breast cancer: A propensity-matched analysis from the prospectively maintained database.

Abstract

538 Background: There are limited data on endocrine therapy benefits for patients with estrogen receptor (ER)-low positive breast cancer (staining 1% to 10% of tumor nuclei by immunohistology). We aimed to compare the effect of short-term 2-3 years versus standard 5 years of adjuvant endocrine therapy on survival outcomes in patients with ER-low positive early breast cancer. Methods: We used data from the prospectively maintained Breast Surgery Database of Fudan University Shanghai Cancer Center for this propensity-matched analysis. Women with ER-low positive, operable, and unilateral early-stage invasive ductal breast cancer were enrolled in this study. Patients with advanced disease, having received neoadjuvant chemotherapy or ovarian function suppression, or with unknown duration or longer than 5 years of adjuvant endocrine therapy were excluded. Enrolled patients were divided into three groups: received no endocrine therapy; received 2-3 years of endocrine therapy; and received approximately 5 years of endocrine therapy. The primary endpoint was disease-free survival (DFS). Multivariate Cox regression analysis and propensity score matching were performed to minimize bias. Hazard ratios (HR) with 95% CIs were calculated. Results: From 2012 to 2017, 634 patients with ER-low positive breast cancer in the database met the inclusion criteria. At a median follow-up of 60 months (interquartile range, 46-74), the 5-year DFS of the whole cohort was 84.9%, with 77.6% for patients who received no endocrine therapy (N = 89), 83.7% for patients who received 2-3 years endocrine treatment (N = 185), and 87.5% for patients who received 5 years endocrine therapy (N = 360). When compared with those receiving no endocrine therapy, patients receiving 5 years treatment was associated with a significantly improved DFS (HR, 0.55; 95% CI 0.32-0.95; P = 0.03); however, there was no significant difference in DFS between patients receiving 2-3 years and 5 years endocrine therapy (HR, 0.79; 95% CI, 0.48-1.28; P = 0.33). In the multivariate Cox regression analysis of the propensity score-matched samples of 360 patients, the DFS was not significantly better for patients who received 5 years of endocrine therapy than 2-3 years treatment (HR, 0.74; 95% CI 0.41-1.34; P = 0.32). An exploratory analysis of re-biopsy of the recurrence lesions indicated more than half of relapsed disease displayed ER-negative, and less than 5% lesions were proved to be ER ≥10% positive. Conclusions: Our data did not support the necessity of 5 years duration of endocrine therapy for patients with ER-low positive breast cancer. Short-term 2-3 years duration might be an alternative option. Further translational research on identifying endocrine-sensitive cases within ER-low positive patients is needed.