Varying levels of family history of breast cancer in relation to mammographic breast density (United States).

Objective: We examined the relationship between breast cancer family history and mammographic breast density.

Methods: Participants included 35,019 postmenopausal women aged >or=40 years enrolled in a population-based mammography screening program. We collected data on the number and type of 1st and 2nd degree female relatives with a history of breast cancer and their ages at diagnosis.