Breast Density and Breast Cancer Risk: Understanding of Biology and Risk

Mammographic density is a strong risk factor for breast cancer, independent of other known risk factors. While a number of hypotheses have been proposed, the biological mechanisms underlying the association between mammographic density and breast cancer remain, however, largely unknown. Understanding these mechanisms may help identify opportunities to reduce mammographic density and ultimately breast cancer risk. We review three major areas of research that may help us better understand the biologic underpinnings of mammographic density: heritability and genetics, breast tissue histology and (molecular) pathology, and experimental studies. We summarize the main consistent findings in the literature and identify key areas for future research.