Breast cancer subtypes in Asian-Americans differ according to Asian ethnic group.

Breast cancer prognosis and breast cancer molecular subtype vary by race/ethnicity. We determined whether the distribution of breast cancer subtypes varies among different Asian ethnic groups. Using immunohistochemical surrogates for the four molecularly defined breast cancer subtypes, we characterized breast cancer subtype for 346 Asian subjects treated at two New York City institutions. We found that Chinese and Japanese had a higher proportion of good-prognosis luminal A cancers (66.7 and 80.0%, respectively) compared to Filipinos and Koreans (48.5 and 47.1%) (P = 0.001). Filipinos had a higher proportion of HER-2/neu positive cancers (45.6%) compared to other ethnic groups (23.6%) (P = 0.002).Koreans had a higher proportion of triple negative cancers(23.5%) compared to other ethnic groups (7.5%) (P =0.06). The results suggest that differences exist in breast cancer tumor biology among distinct Asian ethnic groups and have implications for cancer care and research. Future studies of breast cancer in Asian-Americans should distinguish among the different ethnic groups.