Treatment and prognosis of patients with hormone receptor-low positive (1%-10%) breast cancer: a retrospective propensity score-matched analysis.

OBJECTIVE

This study aimed to investigate the clinicopathological characteristics, treatment patterns, and survival outcomes of hormone receptor (HR)-low positive (1%-10%) breast cancer, with a focus on evaluating the prognostic impact of endocrine therapy (ET) and its interplay with HR-low positive categories (ER-low/PR-low, ER-low/PR-negative, ER-negative/PR-low).

METHODS

A retrospective analysis of 16,578 patients with stage I-III breast cancer (July 2009 to December 2019) identified 388 HR-low positive cases. Propensity score match (PSM) was used to balance baseline characteristics in two comparisons: (1) HR-low positive patients receiving ET vs. HR-negative patients; (2) HR-low positive patients with vs. without ET. 5-year disease-free survival (DFS) and breast cancer-specific survival (BCSS) were analyzed via Kaplan-Meier and Cox regression analyses. Subgroup and interaction analyses assessed ET efficacy across HR-low positive categories.

RESULTS

HR-low positive tumors (2.34%) exhibited clinicopathological similarities to HR-negative tumors but distinct from HR-positive tumors. ET administration significantly improved DFS of HR-low positive patients compared to HR-negative counterparts (84.89% vs. 75.87%; HR = 0.59 [0.37-0.93], P = 0.024). Within HR-low positive cohort, ET omission was significantly associated with a 74% increased risk of DFS compared to ET-treated patients (75.54% vs. 85.37%; HR = 1.74 [1.01-3.00], P = 0.047). ET duration (1-4 vs. 5 years) did not affect survival outcomes (DFS: P = 0.533; BCSS: P = 0.675). Multivariate analysis confirmed ET omission as an independent risk factor for worse DFS (HR = 1.75 [1.01-3.05], P = 0.046). Subgroup analysis revealed equivalent ET benefit across all HR-low positive categories (P for interaction > 0.9).

CONCLUSION

HR-low positive breast cancer has similar clinicopathological characteristics and therapeutic options with HR-negative disease but derives significant DFS benefits from ET, irrespective of ET duration or HR category. These findings support integrating ET into standard management protocol for HR-low positive breast cancer to ameliorate survival outcomes.