Within the NCI Cohort Consortium, the Breast and Prostate Cancer Consortium (BPC3; http://epi.grants.cancer.gov/BPC3/) was launched in 2003 and was first funded to conduct collaborative studies of hormone-related gene variants and environmental factors involved in the development of breast and prostate cancer. This research involved 10 U.S. and European cohorts and pooled data on nearly 9,000 patients with prostate cancer and over 6,000 patients with breast cancer. The goal was to characterize common variations in about 55 candidate genes that mediate the steroid hormone metabolism and insulin-like growth factor signaling pathways, and associate these variations with cancer risk. In 2007, the BPC3 Consortium received funding from the NCI to expand the number of cases/controls to 14,000 and 16,000 for breast and prostate cancer, respectively. Current and future efforts of BPC3 will utilize a genome-wide association approach to identify genetic variants that may be associated with estrogen receptor negative (ER-) breast cancer, as well as aggressive forms of prostate cancer.