Clinical Characteristics and Outcomes of Single Versus Double Hormone Receptor–Positive Breast Cancer in 2 Large Databases

Purpose To identify biologic and outcome differences between double hormone receptor (HR)-positive (dHR+, estrogen receptor (ER)+/progesterone receptor [PgR+]) and single HR-positive (sHR+, either ER+/PgR− or ER−/PgR+) breast cancer; and to explore whether hormone therapy (HT) response in HER2-negative breast cancer correlates with HR status. Patients and Methods This retrospective study was conducted by using 2 large breast cancer databases: the Surveillance, Epidemiology, and End Results (SEER) database and the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) clinical data set. Cox regression analysis was used to estimate overall survival (OS) and breast cancer–specific survival (BCSS) among sHR+ and dHR+ patients. Results In the SEER database, dHR+ patients had significantly longer OS and BCSS than ER+/PgR− patients in short-term follow-up (OS: hazard ratio = 0.620; 95% confidence interval [CI], 0.590, 0.652; P < .001; BCSS: hazard ratio = 0.493; 95% CI, 0.462, 0.526; P < .001). Meanwhile, ER−/PgR+ patients had younger age, larger tumor size, and higher disease grade than dHR+ and ER+/PgR− patients. In patients who received HT, dHR+ patients had a more favorable OS than ER+/PgR− patients (hazard ratio = 0.789; 95% CI, 0.635, 0.982; P = .034), and ER−/PgR+ patients had a worse OS than ER+/PgR− patients at 10 years’ follow-up (hazard ratio = 7.991; 95% CI, 1.053, 60.644; P = .044). However, these groups had similar outcomes over longer periods. Conclusion In HER2-negative breast cancer, sHR+ patients are associated with relatively worse characteristics and worse short-term outcomes than dHR+ patients. Additionally, the outcome of patients receiving HT may differ according to the HR status. However, further studies are needed to confirm these conclusions.