Clinicopathological Characteristics and Breast Cancer–Specific Survival of Patients With Single Hormone Receptor–Positive Breast Cancer

Importance: Steroid hormone receptors, including estrogen receptor (ER) and progesterone receptor (PR), are crucial biomarkers in breast cancer (BC). However, limited data are available regarding single hormone receptor-positive (ER-positive/PR-negative and ER-negative/PR-positive) subtypes, rendering treatment decision and survival forecast difficult in patients with these BC subtypes. Objective: To investigate the clinicopathological characteristics and BC-specific survival (BCSS) of patients with single hormone receptor-positive BC. Design, Setting, and Participants: In this cohort study, data on patients diagnosed with BC between 1990 and 2015 were retrieved from the Surveillance, Epidemiology, and End Results database (N = 1 158 032). Patients lacking information on ER status, PR status, or BCSS were excluded (n = 334 633). Comparisons were performed between single hormone receptor-positive BC and double hormone receptor-positive/double hormone receptor-negative BC. The dates of analysis were September 1, 2018, to June 31, 2019. Main Outcomes and Measures: The BCSS of patients with single hormone receptor-positive BC. Results: This cohort study included 823 399 patients with BC (818 002 women and 5397 men). The median (range) age at diagnosis was 60 (8-108) years, and the median (range) follow-up duration was 71 (0-311) months. The percentages of ER-positive/PR-positive, ER-positive/PR-negative, ER-negative/PR-positive, and ER-negative/PR-negative cases were 67.2%, 12.2%, 1.6%, and 19.0%, respectively. Single hormone receptor-positive subtypes showed distinct clinical characteristics compared with double hormone receptor-positive/double hormone receptor-negative subtypes. Multivariable Cox proportional hazards regression analysis showed that patients with ER-positive/PR-negative (hazard ratio [HR], 1.36; 95% CI, 1.34-1.38) and ER-negative/PR-positive (HR, 1.61; 95% CI, 1.55-1.67) tumors had worse BCSS than patients with the ER-positive/PR-positive subtype. In contrast, patients with ER-positive/PR-negative (HR, 1.27; 95% CI, 1.24-1.29) and ER-negative/PR-positive (HR, 1.07; 95% CI, 1.03-1.11) tumors had better BCSS than patients with the ER-negative/PR-negative subtype. The BCSS was statistically significantly worse in patients with ER-negative/PR-positive tumors than in patients with ER-positive/PR-negative tumors (HR, 1.18; 95% CI, 1.14-1.23). Conclusions and Relevance: In this cohort study, statistically significant distinctions between survival rates of patients with single hormone receptor-positive BC vs double hormone receptor-positive/double hormone receptor-negative BC were observed. Different strategies may be required for patients with single hormone receptor-positive tumors to ensure optimal treatment and maximum benefits from therapies.