Background: Breast cancer is not a homogeneous disease, but several different and unique subtypes defined by gene expression analysis. Incidence and mortality rates vary by almost 3-fold between Alaska (highest) and the Southwestern tribes (lowest). We hypothesized that these differences may be due to, in part, varying levels of biologic tumor aggressiveness. Methods: A biorepository of the North Central Cancer Treatment Group with 95 cases of American Indian and Alaska Native (AIAN) women with adenocarcinoma of the breast surgically treated from 1990 to 2000 was tested for several biomarkers. Comparison distributions of biomarker values across state of residence using t tests for continuous (p53, MIB-1, cyclin D) and ordinally scaled markers [EGF receptor (EGFR), BCL-2, Her2] and c2 tests of significance for binary markers [estrogen receptor (ER), progesterone receptor (PR)] were done. Results: Significant regional differences in some biomarker expression levels were seen. No increase was observed in "triple-negative" breast cancer or Her2 overexpression in these cases. Conclusions: Despite a 3-fold difference in breast cancer mortality in Alaska Native versus Southwestern American Indians, standard biomarkers such as ER, PR, and Her2 neu expression did not explain the disparity. Impact: There is a need for research to understand the biologic basis of breast cancer disparities in AIAN women. Potential for a prospective trial will be explored with tribes.
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