Genetic Ancestry of 1127 Brazilian Breast Cancer Patients and Its Correlation With Molecular Subtype and Geographic Region.

Purpose: Breast cancer molecular subtypes show significant differences in different ethnic groups in the United States, but no study has evaluated genetic ancestry in breast cancer in Brazilian women.

Methods: Breast cancer patients from distinct parts of Brazil were evaluated. Molecular subtypes were determined by immunohistochemistry. Genetic ancestry was evaluated using a panel of 46 AIMs (ancestry informative markers), which classified genetic ancestry as European, African, Asian, and Amerindian. PCR products were subjected to capillary electrophoresis and analyzed using GeneMapper 4.0 software. Ancestry was evaluated with Structure v.2.3.3 software. Ancestry was tested for correlations with geographic region and molecular subtype. The chi-square test and ANOVA with Bonferroni adjustment were applied.

Results: Genetic ancestry and clinical data were evaluated in 1127 patients. Higher rates of self-reported white ethnicity, European ancestry, and HER-2 luminal tumors were identified in the South region, which may influence age at diagnosis and result in a higher rate of early tumors. Conversely, higher rates of African ancestry in the North and Northeast regions, self-reported nonwhite ethnicity, HER-2 tumors, and triple-negative tumors were noted. Triple-negative and HER-2 tumors were associated with higher advanced and metastatic disease rates at diagnosis, with triple-negative tumors being more frequent in young women.

Conclusion: Differences in genetic ancestry, self-reported ethnicity, and molecular subtype were found between Brazilian demographic regions. Knowledge of these features may contribute to a better understanding of age at diagnosis and the molecular distribution of breast cancer in Brazil.