Single Hormone Receptor-Positive Breast Cancers Have Distinct Characteristics and Survival

Estrogen receptor (ER) and progesterone receptor (PR) status is pivotal to determining the prognosis and treatment of human epidermal growth factor 2 (HER2) receptor-negative invasive breast cancer. Frequently ER-positive (ER+) and/or PR-positive (PR+) cancers are labeled nonspecifically as “hormone receptor-positive” although only one is positive. This study aimed to evaluate and characterize the ER+PR− and ER−PR+ breast cancer phenotypes in reference to ER+PR+ cancers. A retrospective cohort study of female patients with HER2-negative (HER2−) invasive breast cancer diagnosed in 2010−2015 was performed using the National Cancer Database. Cases were grouped into ER+PR+, ER−PR+, ER+PR−, and ER−PR− phenotypes to determine differences in patient demographics, tumor characteristics, and overall survival. Of 823,969 cases, 619,050 (75.1%) were ER+PR+, 79,777 (9.7%) were ER+PR−, 7006 (0.9%) were ER−PR+, and 118,136 (14.3%) were ER−PR−. Compared with the ER+PR+ group, the ER+PR− and ER−PR+ groups were more likely to be high-grade cancer (16.0% vs. 34.2% and 80.0%, respectively; p < 0.001), to have lymphovascular invasion (17.9% vs. 19.6% and 23.0%; p < 0.001), to be node-positive (13.5% vs. 19.7% and 26.3%; p < 0.001), to be stage 4 cancer (3.6% vs. 5.9% and 6.7%; p < 0.001), to have a higher multigene assay score (mean, 16.0 vs. 27.8 and 38.1; p < 0.001), and to have a worse survival (90.6% vs. 83.8% and 78.1%; p < 0.001). Single hormone receptor-positive breast cancer subtypes (ER+PR− and ER−PR+) are more likely to have unfavorable characteristics and worse survival than the ER+PR+ subtype, with the ER−PR+ subtype having outcomes similar to those for ER−PR− cancers. The single hormone receptor-positive subtypes, representing 10% of HER2− cancers, should be considered clinically distinct from ER+PR+ disease.