Eliminating cancer health disparities remains a high priority of the National Cancer Institute, and one of the most promising avenues for reducing the burden of cancer. Our nation's investment in cancer research has contributed to many breakthroughs in our knowledge of biomedical and behavioral risk factors. However, to effectively intervene on these risk factors, we must also understand the social contexts within which individual risks are developed and lead to persistent cancer health disparities. My goal in seeking this career development award is to become an independent researcher in the field of cancer health disparities, with a focus on multilevel research and intervention in racial/ethnic minority and socioeconomically disadvantaged communities. To leverage my existing training in social science research and cancer epidemiology, I propose additional training in applied intermediate marker and biomarker research, cancer prevention and control, community-engaged intervention research, and advanced statistical methods. An experienced interdisciplinary team of mentors will provide the necessary and complementary expertise and mentorship. My proposed research will examine the associations of social network characteristics (social integration, social support) and the metabolic syndrome (clustering of high blood glucose level, dyslipidemia, high blood pressure, abdominal obesity) with breast cancer risk and with mammographic breast density, a strong biomarker of breast cancer risk. I will investigate these aims in two separate study populations of Hispanic, African American, and White women, recruited from a socioeconomically disadvantaged community in New York City. I will build on extensive interview, clinical and biomarker data already available for these studies by obtaining the following data: neighborhood social environment (from U.S. Census data and previously constructed built environment data), breast density (measured from routine mammograms using validated computer-assisted methods) and breast cancer diagnosis (through review of medical and pathology records). Based on these results and in partnership with community representatives, I will conduct formative qualitative and quantitative research to guide the development of multilevel intervention strategies for breast cancer risk reduction. Together, these research activities will increase my understanding of the social environment characteristics, mediating behavioral factors, and biological pathways associated with breast cancer risk and increase my skills in community-engaged research and intervention development. Ultimately, this program of research will be applied to prevention of breast cancer risk through community-based interventions in low socioeconomic, racial/ethnic minority communities.