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

Background. 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. Methods. 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. Results. 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). Conclusion. 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.