All women, regardless of their racial or ethnic origin or heritage, are at risk of developing breast cancer. Variations in breast carcinoma incidence rates among multicultural populations suggest that etiologic factors differ in their biologic expression and impact on disease outcome. Key among those factors that affect breast carcinoma development are the roles of genetics and the environment, the reproductive experience and the effects of endogenous and exogenous hormones in women, the change in immune status and host vulnerability, and the biologic determinants of breast carcinoma. Cultural dynamics, sociodemographic differences, and behavioral characteristics across population subgroups modulate how biologic disease is expressed among different races and ethnic groups. These interactions contribute to the observed variations in breast carcinoma incidence, mortality, and survival. Stage, a measure of disease status, is used to assess prognosis, plan treatment, and evaluate outcome. Numerous studies have reported a more advanced stage of breast carcinoma at diagnosis in racial/ethnic subgroups, especially among women from African American, Hispanic, American Indian, and native Hawaiian cultures. Factors associated with advanced stage at diagnosis in multicultural populations range from changes in the basic biological characteristics at the molecular and cellular level, to more complex behavioral attributes unique to a particular multicultural population, to societal issues—such as access to care and socioeconomic conditions—all of which impact on the health measure called “stage at diagnosis.” Rapid advancements in knowledge of cancer biology and of genetic markers and tumor products are providing new mechanisms for identifying etiologic pathways that can be utilized for better screening, detection, treatment and monitoring of disease. Further studies are needed that evaluate the biologic and molecular alterations in tumor development, progression, and response to therapy. Public health attention needs to be directed toward the societal influences that impact breast carcinoma development, as well as augmenting recognition of the need for culturally appropriate, broad-based behavioral changes at the community level. In addition, continued efforts are needed to ensure the inclusion of multicultural population subgroups and minority investigators in all aspects of research—basic, clinical and applied. Cancer 2000;88:1193–1202. © 2000 American Cancer Society.