Family history, mammographic density, and risk of breast cancer Free

B77

Background. Mammographic density is a strong and highly heritable risk factor for breast cancer that may explain some of the effect of family history on risk. We have examined the association of family history with mammographic density and breast cancer risk.
 >Methods. We have carried out 3 nested case-control studies in screening programmes, with 1114 matched case-control pairs. We have examined in these studies combined the associations of family history and percent mammographic density at baseline with subsequent risk of breast cancer.
 >Results. After adjustment for age and other risk factors, compared to women with no affected first-degree relatives, mammographic density was 3% greater in those with 1 affected degree, and 5.6% greater in those with 2 or more affected relatives. The odds ratios for risk of breast cancer were respectively 1.37 (95% CI: 1.10, 1.72) for those with 1 affected relative, and 2.46 (95% CI: 1.30, 4.63) for those with 2 or more affected relatives (p for trend 0.0002). Adjustment for percent density reduced the odds ratio for 1 affected first-degree relatives by 16%, and for 2 or more affected relatives by 15%.
 >Conclusions. As predicted, percent mammographic density explained about 16% of the effect of family history on risk of breast cancer. Mammographic density has features of an intermediate phenotype for breast cancer and some of the genes associated with density may also be associated with risk of breast cancer.