Genetic epidemiology of breast cancer in younger women.

Genetics plays a role in all of breast cancer. At present, however, inherited genes associated with the development of breast cancer have more frequently been identified in women with an early age at onset. This review examines the extent to which genetic information, at both an epidemiologic and molecular level, may be used to identify a subset of women who are likely to be at increased risk of developing breast cancer at an early age.