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 = 1158032). Patients lacking information on ER status, PR status, or BCSS were excluded (n = 334633). 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 823399 patients with BC (818002 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. This cohort study investigates the clinicopathological characteristics and breast cancer-specific survival of patients with single hormone receptor-positive breast cancer. Question Are single hormone receptor-positive tumors distinct groups of breast cancer? Findings This cohort study analyzed 823399 patients with breast cancer and showed that patients with single hormone receptor-positive subtypes had worse breast cancer-specific survival (BCSS) than patients with double hormone receptor-positive subtypes but better BCSS than patients with double hormone receptor-negative subtypes, and the differences were statistically significant. Patients with single estrogen receptor-positive subtypes had statistically significantly better BCSS than those with single progesterone receptor-positive subtypes. Meaning Future studies aimed at developing optimized treatment strategies for patients with single hormone receptor-positive tumors may be warranted.