MAMMOGRAPHIC FEATURES AND BREAST-CANCER RISK - EFFECTS WITH TIME, AGE, AND MENOPAUSE STATUS

Background: Mammographic images from women with a high proportion of e pithelial and stromal breast tissues are described as showing high-den sity parenchymal patterns. Most past studies that noted an increase in breast cancer risk associated with mammographic parenchymal patterns showing high density either 1) lacked information on other breast canc er risk factors, 2) were too small, or 3) included insufficient follow -up time to adequately resolve persisting doubts whether mammographic features are ''independent'' measures of breast cancer risk and not a detection artifact, Purpose: The purpose of this study was twofold: 1) to evaluate the associations between mammographic features and other breast cancer risk factors and 2) to assess effects of mammographic fe atures on breast cancer risk by time, age, and menopause status, Metho ds: To address these questions, we analyzed detailed information from a large, nested case-control study with 16 years of follow-up, This st udy used information from both screening and follow-up phases of the B reast Cancer Detection Demonstration Project, a nationwide program tha t offered annual breast cancer screening for more than 280 000 women f rom 1973 to 1980, Mammographic features were assessed from the base-li ne screening mammographic examination for 1880 incident case subjects and 2152 control subjects, Control subjects were randomly selected fro m women of the same age and race as each case subject, Control subject s attended the same screening center as the case subject and were free of breast cancer at the case subject's date of diagnosis, Odds ratios (ORs) with 95% confidence intervals (CIs) provided estimates of the r elative risk of breast cancer, Results: Mammographic features were ass ociated with known breast cancer risk factors, However, the high-densi ty parenchymal pattern effects were independent of family history, age at first birth, alcohol consumption, and benign breast disease, The i ncreased risk for women with Wolfe's two high-density parenchymal patt erns, P2 (OR = 3.2; 95% CI = 2.5-4.0) and Dy (OR = 2.9; 95% CI = 2.2-3 .9), was explained primarily by measured percent of the breast with de nse mammographic appearance, Compared with women with no visible breas t density, women who had a breast density of 75% or greater had an alm ost fivefold increased risk of breast cancer (95% CI = 3.6-7.1), These effects persisted for 10 or more years and were noted for both premen opausal and postmenopausal women of all ages. Conclusions: Of the brea st cancer risk factors assessed in the participants, high-density mamm ographic parenchymal patterns, as measured by the proportion of breast area composed of epithelial and stromal tissue, had the greatest impa ct on breast cancer risk, Of the breast cancers in this study, 28% wer e attributable to having 50% or greater breast density.