Breast Cancer Subtypes as Defined by the Estrogen Receptor (ER), Progesterone Receptor (PR), and the Human Epidermal Growth Factor Receptor 2 (HER2) among Women with Invasive Breast Cancer in California

Breast cancer research examining either molecular profiles or biomarker subtypes has focused on the estrogen receptor negative/progesterone receptor negative/human epidermal growth factor receptor 2 negative (ER-/PR-/HER2-) and ER-/PR-/HER2+ subtypes. Less is known about the epidemiology or clinical outcome of the other subtypes. This study examines the eight combinations of ER/PR/HER2 in patients with invasive breast cancer. The 5-year relative survival and the distribution among demographic, socioeconomic, and tumor characteristics of each of the subtypes are examined. Using the California Cancer Registry, 61,309 women with primary invasive breast cancer were classified according to ER/PR/HER2 status. Five-year relative survival was computed for the eight subtypes. Bivariate analyses were used to assess the distribution of cases across all subtypes. Multivariate logistic regression was used to compute the adjusted odds of having one of the five subtypes with the best and worst survival. Survival varied from 96% (ER+/PR+/HER2-) to 76% (ER-/PR-/HER2+ and ER-/PR-/HER2-). The four subtypes with the poorest survival were all ER negative. Women who were younger than age 50, non-Hispanic black or Hispanic, of the lowest SES groups, and had stage IV tumors that were undifferentiated were overrepresented in ER-/PR-/HER2+ and triple negative (ER-/PR-/HER2-) subtypes. Asian Pacific Islanders had increased odds (OR = 1.41; 95% confidence interval [CI] = 1.26-1.57) of having the ER-/PR-/HER2+ subtype. Stage III tumors (OR = 1.25; 95% CI = 1.08-1.44) and stage IV tumors (OR = 1.58; 95% CI = 1.27-1.98) had higher odds than stage I tumors of being ER-/PR-/HER2+. Stage IV tumors (OR = 0.54; 95% CI = 0.44-0.67) strongly decreased the odds of the ER-/PR-/HER2- subtype. Poorly differentiated and undifferentiated tumors were over 20 times as likely as well-differentiated tumors of being ER-/PR-/HER2- or ER-/PR-/HER2+. There are considerable differences in survival, demographics, and tumor characteristics among the eight subtypes. We recommend reporting breast cancer as an ER/PR/HER2 subtype and precisely documenting demographic and tumor characteristics.