Differences in breast cancer subtype distribution exist among ethnic subgroups of Asian women in California.

Abstract

Abstract Abstract #2088 Background: Distinct breast cancer subtypes have been identified by gene expression analysis. Little is known about the distribution of these subtypes among Asian women. We previously reported an increased frequency of HER2-positive breast cancers among certain ethnic subgroups of Asian women in California. To follow up on that finding in detail, we undertook the current analysis to explore factors associated with differences in breast cancer subtype distribution among Asian women in California.
 Methods: We defined immunohistochemical surrogates for each breast cancer subtype among Chinese, Japanese, Filipina, Korean, Vietnamese and South Asian patients in the population-based California Cancer Registry diagnosed in the period 1999-2005. Subtypes were defined using combinations of immunohistochemical markers: luminal A (ER+ and/or PR+, HER2-), luminal B (ER+ and/or PR+, HER2+), basal-like (ER-, PR-, HER2-) and HER2+/ER- (ER-, PR-, HER2+). Polytomous logistic regression was used to evaluate associations between breast cancer subtype and age, race, AJCC stage, tumor grade, tumor histology, socioeconomic status, nativity and hospital ownership (private vs. public). Models were used to compare differences in these characteristics simultaneously across the four breast cancer subtypes.
 Results: Of 12,245 Asian women diagnosed with invasive breast cancer, 7,217 (59%) women had data for all three immunohistochemical markers. The majority of breast cancers among Japanese women were of the luminal A subtype (67%), with a low frequency of basal-like (10%) and HER2+ (22%) cancers. Korean, Filipina and Vietnamese women had a high frequency of HER2+ cancers (35%, 31% and 31%, respectively) compared to Non-Hispanic White women diagnosed during this period (n=12,996, 21%). In regression analyses among Asian women, the four subtypes varied significantly in their associations with age group (p=0.01), detailed Asian ethnicity (p<0.0001), stage (p<0.0001), grade (p<0.0001), histology (p<0.0001), year of diagnosis (continuous; p=0.03) and hospital ownership (p<0.0001). However, there was no significant variation among the subtypes in their relationships with socioeconomic status (p=0.94) or nativity (p=0.29).
 Conclusions: Differences in the distribution of breast cancer subtypes exist among Asian women according to ethnicity, as well as other demographic and disease characteristics. These differences were not associated with place of birth or socioeconomic status. Breast cancers among Japanese women had the most favorable subtype distribution, while Korean women had the least favorable distribution. Further study may identify genetic and environmental risk factors responsible for these differences, with implications for prevention and treatment. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2088.