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.