Disparities in the risk of the ER/PR/HER2 breast cancer subtypes among Asian Americans in California

BACKGROUND: Population-based studies of breast cancer often aggregate all Asians into a single category termed Asian/Pacific Islander (API). PURPOSE: (1) Describe the demographic and clinicopathologic features of early breast cancer utilizing all eight ER/PR/HER2 subtypes among white, black, Hispanic, American Indian, seven Asian ethnicities, and the aggregate API category; (2) ascertain the risk of the ER+/PR+/HER2+, ER-/PR-/HER2-, and ER-/PR-/HER2+ subtypes when compared with the ER+/PR+/HER2- subtype, among seven Asian ethnicities versus non-Hispanic white women and (3) contrast the results with the risk of these same subtypes when using the aggregate API category. METHODS: Using the California Cancer Registry, we identified 225,441 cases of stages 1-4 first primary female invasive breast cancer. Logistic regression was used to assess the association of race with the ER+/PR+/HER2+, ER-/PR-/HER2- (triple-negative), and the ER-/PR-/HER2+ subtypes versus the ER+/PR+/HER2- when adjusted for stage, age, tumor grade, and socioeconomic status. Models were fit separately for each subtype. Odds ratios for the seven Asian ethnicities and the aggregate API category using non-Hispanic white women as the reference category were computed. RESULTS: There was an increased risk of the ER+/PR+/HER2+ subtype for the combined API category (OR=1.16; 95% CI=1.09-1.23). But only Southeast Asians (OR=1.17; 95% CI=1.04-1.31), Filipino (OR=1.23; 95% CI=1.12-1.36), and Korean (OR=1.63; 95% CI=1.38-1.99) women had an increased risk of this subtype. The reduced risk of the triple-negative subtype seen in APIs (OR=0.84; 95% CI=0.79-0.90) was only noted in Chinese (OR=0.80; 95% CI=0.70-0.91) and Filipino (OR=0.65; 95% CI=0.58-0.73) women whereas Indian Continent (OR=1.25; 95% CI=1.01-1.53) women had an increased risk of the triple-negative subtype. The racexstage interaction was statistically significant for the ER-/PR-/HER2+ subtype (p