Mammographic parenchymal features and breast cancer in the breast cancer detection demonstration project.

The Breast Cancer Detection Demonstration Project (BCDDP) screened 283,222 U.S. women for breast cancer by use of mammography and breast palpation. A sample of participants was followed up to determine the subsequent occurrence of breast cancer cases and deaths. We have used information from the BCDDP to evaluate the relation of mammographic parenchymal features to the incidence of and mortality from breast cancer, and to examine changes in this relation with duration of follow-up. We also reevaluated the relations of age, body weight, height, menopause, parity, and age at birth of first child to mammographic features of breast tissue. Among women 35-49 years of age at entry, those whose mammographic features were "glandular" or "homogeneously dense" had a 2.8-fold increase in risk of breast cancer compared to women whose mammographic features were "atrophic or fatty". The increased risk was observed up to 9 years after entry. Among women 50-74 years of age at entry, the risk of breast cancer was elevated by a factor of 1.7 for women with glandular or dense breast parenchyma compared to those with atrophic or fatty breasts. The increase in risk, however, diminished with increasing follow-up. The percentage of women with glandular or dense parenchymal features decreased as age, body weight, and parity increased. The percentage with glandular or dense features increased as height increased, and the percentage decreased with menopause. Mammographic parenchymal features were not associated with age at birth of first child.