Population-based relative risks for specific family history constellations of breast cancer.

The majority of females in the Utah resource had a positive family history of BC in FDRs to TDRs. Presence of any number of affected FDRs or SDRs significantly increased risk for BC over population risk; and more than four TDRs, even with no affected FDRs or SDRs, significantly increased risk over population risk. Risk prediction derived from the specific and extended family history constellation of affected relatives allows identification of females at increased risk even when they do not have a conventionally defined high-risk family; these risks could be a powerful, efficient tool to individualize cancer screening and prevention.