IMPORTANCE: Variation in cancer incidence and outcome has well-documented correlations with racial/ethnic identity. In the United States, the possible genetic and ancestral hereditary explanations for these associations are confounded by socioeconomic, cultural, and lifestyle patterns. Differences in the breast cancer burden of African American compared with European/white American women represent one of the most notable examples of disparities in oncology related to racial/ethnic identity. Elucidating the source of these associations is imperative in achieving the promise of the national Precision Medicine Initiative. OBSERVATIONS: Population-based breast cancer mortality rates have been higher for African American compared with white American women since the early 1980s, largely reflecting declines in mortality that have been disproportionately experienced among white American patients and at least partly explained by the advent of endocrine therapy that is less effective in African American women because of the higher prevalence of estrogen receptor-negative disease. The increased risk of triple-negative breast cancer in African American women as well as western, sub-Saharan African women compared with white American, European, and east African women furthermore suggests that selected genetic components of geographically defined African ancestry are associated with hereditary susceptibility for specific patterns of mammary carcinogenesis. Disentangling health care access barriers, as well as reproductive, lifestyle, and dietary factors from genetic contributions to breast cancer disparities remains challenging. Epigenetics and experiences of societal inequality (allostatic load) increase the complexity of studying breast cancer risk related to racial/ethnic identity. CONCLUSIONS AND RELEVANCE: Oncologic anthropology represents a transdisciplinary field of research that can combine the expertise of population geneticists, multispecialty oncologists, molecular epidemiologists, and behavioral scientists to eliminate breast cancer disparities related to racial/ethnic identity and advance knowledge related to the pathogenesis of triple-negative breast cancer.