Two of the strongest risk factors for breast cancer are the presence of a mutation in BRCA1 or BRCA2, and increased mammographic density. It is estimated that the risk of early-onset breast cancer is increased by 25-fold in women who carry a pathogenic mutation in either BRCA1 or BRCA2. It is also estimated that women who are in the highest quintile of mammographic density experience a five-fold increase for breast cancer. However, it is not known if the two risk factors are independent. If so, then women with a BRCA1 or BRCA2 mutation who also show high density patterns on a screening mammogram will form a subgroup at particularly high risk. It is important to establish the magnitude of this association if accurate risk estimates are to be given in a clinical setting. There is considerable interest in identifying intermediate markers of risk for chemoprevention studies in high-risk women. One potential marker is mammographic density. However, prior to the acceptance of mammographic density as a surrogate marker of risk in BRCA1 and BRCA2 carriers, it is essential to establish whether or not this risk factor is relevant for hereditary breast cancer. The present study is a case-control study of 120 hereditary breast cancer cases and 120 unaffected age-matched carrier controls. Screening mammograms performed prior to the occurrence of breast cancer in the case will be evaluated for mammographic density and compared with those of the controls. Relative risks for mammographic density will be estimated by degree of mammographic density.
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