Survival and prognostic factors in patients with de novo metastatic breast cancer according to estrogen receptor status: A retrospective study

Abstract Purpose: The clinical outcomes of de novo metastatic breast cancer (dnMBC) differ between estrogen receptor (ER)-positive and ER-negative patients, but the respective prognostic factors in these two subpopulations have not been established. This study aimed to investigate the survival and prognostic factors in patients with dnMBC according to ER status. Methods: Patients with dnMBC between February 2010 and December 2017 were retrospectively reviewed. Demographics, tumor characteristics, treatment types and survival data were collected. Patients were divided into ER-negative and ER-positive groups, and the propensity score matching (PSM) was used to balance the bias. Overall survival (OS) was compared between groups. Univariable and multivariable Cox regression analyses were performed to identify prognostic factors in each group. Results: A total of 518 patients were included in the study. After PSM, there were 157 ER-negative and 165 ER-positive patients. With a median follow-up of 8.5 years, the median OS was 36 months (95% confidence interval [CI], 32-41) in the ER-positive group and 24 months (95% CI, 19-27) in the ER-negative group ( P =0.001). Ki-67 index, endocrine therapy and radiotherapy for primary tumor were independent prognostic factors of OS in the ER-positive group, while initial chemotherapy cycles and chemotherapy after disease progression were independent prognostic factors of OS in the ER-negative group. Clinical T stage and initial metastatic sites were independent prognostic factors of OS regardless of ER status. Conclusion: For dnMBC, ER-negative patients are clinically different from ER-positive patients, with shorter OS. The identified prognostic factors could guide treatment selection in these two subpopulations.