Use of endocrine therapy for estrogen receptor-positive breast cancer among American Indians and Alaska natives.

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American Indian/Alaska Native (AI/AN) women with estrogen receptor-positive (ER +) breast cancer have higher mortality compared to non-Hispanic whites (NHW). The purpose of this study is to compare rates of initiation of endocrine therapy (ET) between AI/AN and NHW and further determine survival outcomes for ER + breast cancer. We used the National Cancer Database to identify patients diagnosed with ER + breast cancer, stage I-III, between 2004 and 2017. Multivariable logistic regression was performed to determine factors associated with initiation of adjuvant ET. Overall survival was estimated using the Kaplan-Meier analysis and Cox proportional hazards modeling. We identified a total of 771,619 patients (AI/AN, n = 2473; NHW, n = 769,146). Compared to NHW, AI/AN patients were more likely to live in rural areas, be younger, and have tumors that were higher grade, node positive, and larger. Initiation of adjuvant ET was high in both groups and not significantly different between AI/AN and NHW. Independent predictors of ET initiation included rural location, age, higher tumor grade, node-positive disease, larger tumor size, and progesterone receptor-positive status. Initiation of ET was significantly associated with improved overall survival among all patients. Overall survival was significantly worse among the AI/AN population. AI/AN race was significantly and independently associated with worse overall survival after diagnosis of ER + breast cancer. We did not find a significant difference in the initiation of adjuvant ET between AI/AN and NHW. Exact reasons why AI/AN women with ER + breast cancer have higher mortality rates remain elusive but are probably multifactorial.