US Incidence of Breast Cancer Subtypes Defined by Joint Hormone Receptor and HER2 Status

Background In 2010, Surveillance, Epidemiology, and End Results (SEER) registries began collecting human epidermal growth factor 2 (HER2) receptor status for breast cancer cases. Methods Breast cancer subtypes defined by joint hormone receptor (HR; estrogen receptor [ER] and progesterone receptor [PR]) and HER2 status were assessed across the 28% of the US population that is covered by SEER registries. Age-specific incidence rates by subtype were calculated for non-Hispanic (NH) white, NH black, NH Asian Pacific Islander (API), and Hispanic women. Joint HR/HER2 status distributions by age, race/ethnicity, county-level poverty, registry, stage, Bloom-Richardson grade, tumor size, and nodal status were evaluated using multivariable adjusted polytomous logistic regression. All statistical tests were two-sided. Results Among case patients with known HR/HER2 status, 36 810 (72.7%) were found to be HR+/HER2(-), 6193 (12.2%) were triple-negative (HR-/HER2(-)), 5240 (10.3%) were HR+/HER2(+), and 2328 (4.6%) were HR-/HER2(+); 6912 (12%) had unknown HR/HER2 status. NH white women had the highest incidence rate of the HR+/HER2(-) subtype, and NH black women had the highest rate of the triple-negative subtype. Compared with women with the HR+/HER2(-) subtype, triple-negative patients were more likely to be NH black and Hispanic; HR+/HER2(+) patients were more likely to be NH API; and HR-/HER2(+) patients were more likely to be NH black, NH API, and Hispanic. Patients with triple-negative, HR+/HER2(+), and HR-/HER2(+) breast cancer were 10% to 30% less likely to be diagnosed at older ages compared with HR+ /HER2(-) patients and 6.4-fold to 20.0-fold more likely to present with high-grade disease. Conclusions In the future, SEER data can be used to monitor clinical outcomes in women diagnosed with different molecular subtypes of breast cancer for a large portion (approximately 28%) of the US population.