Breast Cancer Mortality among Asian-American Women in California: Variation according to Ethnicity and Tumor Subtype

PURPOSE Asian-American women have equal or better breast cancer survival rates than non-Hispanic white women, but many studies use the aggregate term "Asian/Pacific Islander" (API) or consider breast cancer as a single disease. The purpose of this study was to assess the risk of mortality in seven subgroups of Asian-Americans expressing the estrogen receptor (ER), progesterone receptor (PR), or human epidermal growth factor receptor 2 (HER2) tumor marker subtypes and determine whether the risk of mortality for the aggregate API category is reflective of the risk in all Asian ethnicities. METHODS The study included data for 110,120 Asian and white women with stage 1 to 4 first primary invasive breast cancer from the California Cancer Registry. The Asian ethnicities identified were Pacific Islander, Southeast Asian (SEA), Indian Subcontinent, Chinese, Japanese, Filipino, and Korean. A Cox regression analysis was used to compute the risk of breast cancer-specific mortality in seven Asian ethnicities and the combined API category versus white women within each of the ER/PR/HER2 subtypes. Hazard ratios (HRs) and 95% confidence intervals (CIs) were computed. RESULTS For the ER+/PR+/HER2- subtype, the combined API category showed a 17% (HR, 0.83; 95% CI, 0.76-0.91) lower mortality risk. This was true only for SEA (HR, 0.75; 95% CI, 0.61-0.91) and Japanese women (HR, 0.60; 95% CI, 0.45-0.81). In the ER+/PR-/HER2- subtype, SEA (HR, 0.57; 95% CI, 0.38-0.84) and Filipino women (HR, 0.71; 95% CI, 0.51-0.97) had a lower risk of mortality. Japanese (HR, 0.49; 95% CI, 0.25-0.99) and Filipino women (HR, 0.74; 95% CI, 0.58-0.94) had a lower HR for the ER-/PR-/HER2+ subtype. For triple-positive, ER+/PR+/HER2+ (HR, 0.84; 95% CI, 0.71-0.98) and triple-negative, ER-/PR-/HER2- (HR, 0.84; 95% CI, 0.74-0.94) subtypes, only the API category showed a lower risk of mortality. CONCLUSION Breast cancer-specific mortality among Asian-American women varies according to their specific Asian ethnicity and breast cancer subtype.