Associations between sociodemographic and clinicopathological factors and breast cancer subtypes in a population-based study

Purpose: This study examines the factors distinguishing breast cancer (BC) subtypes. Methods: We examined subtypes in 629 women with invasive BC, diagnosed from 2006 to 2012, and enrolled in an epidemiological study in New Jersey. Using molecular characteristics from pathology reports, BCs were categorized as luminal A, luminal B, non-luminal HER2-expressing, or triple-negative breast cancer (TNBC) subtypes. Multinomial logistic models (luminal A as referent) were used to describe BC subtype associations. Results: Women with luminal B tumors were more likely to be younger at diagnosis [odds ratio (OR) 1.8, 95 % confidence interval (CI) 1.0–3.4] and to have higher-grade (OR 2.6, 95 % CI 1.5–4.7), larger (OR 1.9, 95 % CI 1.0–3.6), and Ki67-positive tumors (OR 2.1, 95 % CI 1.1–4.0). Women with non-luminal HER2-expressing BCs were more likely to have higher-grade tumors (OR 14.5, 95 % CI 5.3–39.7). Women with TNBCs were more likely to be African-American (OR 1.9, 95 % CI 1.0–3.4) and to have higher-grade (OR 9.7, 95 % CI 5.1–18.4), larger (OR 2.2, 95 % CI 1.0–4.8), and Ki67-positive (OR 2.9, 95 % CI 1.6–5.2) tumors. Notably, compared to the luminal A subtype, luminal B, non-luminal HER2-expressing, and triple-negative subtypes were more frequently self-detected; however, these associations were attenuated in multivariable models. Conclusions: These findings suggest that some BC subtypes were associated with features denoting more aggressive phenotypes, namely higher grade, larger size, and Ki67 positivity, and possibly patient self-detection among some women. These findings highlight a need for enhanced screening, particularly among younger women, racial/ethnic minorities, and lower socioeconomic subgroups.