Mammographic Features and Breast Cancer Risk: Effects With Time, Age, and Menopause Status by Celia Byrne, Catherine Schairer, John Wolfe, Navin Parekh, Martine Salane, Louise A. Brinton, Robert Hoover, Robert Haile of Environmental Epidemiology Branch, Division of Cancer Etiology, National Cancer Institute, Bethesda, MD, the Department of Radiology, Hutzel Hospital, Detroit, MI and Department of Epidemiology. University of California. Los Angeles, School of Public Health.
Analysis of detailed information from a large, nested case—control study with 16 years of follow-up. This study used information from both screening and follow-up phases of the Breast Cancer Detection Demonstration Project, a nationwide program that offered annual breast cancer screening for more than 280 000 women from 1973 to 1980.
- “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 features on breast cancer risk by time, age, and menopause status.”
- “Of the breast cancer risk factors assessed in the participants, high- density mammographic parenchymal patterns, as measured by the proportion of breast area composed of epithelial and stromal tissue, had the greatest impact on breast cancer risk. Of the breast cancers in this study, 28% were attributable to having 50% or greater breast density.”
- “…consistent twofold to sixfold increased risk of breast cancer associated with various categorizations of patterns of mammographic features.”
- “Increasing total breast size was not associated with higher breast cancer risk in this study.”
- “Regardless of the age of the women at the time of the mammographic examination, breast cancer risk rose with increasing percent density. The relative magnitude of this increase, however, was somewhat greater for older women. Mammographic density measured from either premenopausal or postmenopausal mammograms was associated with an increased risk of breast cancer.”
- “For women with any mammographic density, the breast cancer risk rose twofold. For those women with breast density of 75% or more, the breast cancer risk rose more than fourfold.”
- “In contrast to these other recognized risk factors (28) in which substantially elevated risks apply to a relatively small segment of the population, a large segment of the population has sufficient mammographic density to place it in categories with markedly elevated risk.”
- “The implications of the high prevalence of mammographic density to the attributable risk or etiologic fraction are obvious. Assuming that density is involved in a causal manner with breast cancer risk, then in our study the presence of any density was responsible for 46.2% of all breast cancers, breast density of 50% or more accounted for 28.2%, and breast density of 75% or more explained 8.2% of all breast cancers.”
- “…because the proportion of the breast occupied by mammographic density is one risk factor that may identify a group at high risk for breast cancer, the implications of the findings of this study for intervention, both for screening strategies and prevention trials, should be considered.”
- ” This study, with information from 16 years of the BCDDP, has demonstrated that an easily measured feature from a screening mammographic examination—the percent breast density— had a greater effect on breast cancer risk than most other breast cancer risk factors and could not be explained by these other factors. In addition, percent breast density was not an artifact of a masking bias and applied to women of all ages. Thus, in efforts either to prevent breast cancers or to detect breast cancers earlier, the impact of the percent breast density on breast cancer risk can no longer be ignored.”