Although having increased breast density is one of the strongest risk factors for breast cancer other than increased age and having a BRCA1 or BRCA2 mutation, it is still not clearly understood what that measure of risk is reflecting biologically. It has long been presumed based on indirect evidence that breast density is an indicator of cumulative hormone, particularly estrogen, exposure throughout one's life. However, there is growing evidence that the story may not be that simple. Recent studies suggest that stromal and epithelial proliferation and interaction, and the IGH-axis may all be involved in explaining the breast density and breast cancer risk association. Clearly for breast cancer research to advance it will be necessary to think beyond the presumed association that explains breast density only through estrogen pathways.

There is an established increased risk of secondary malignancy following radiation therapy for cancer in childhood or as a young adult. Breast cancer poses a particular problem as the population risk is significant and screening methods are available raising the question of possible screening interventions for women who are at high lifetime risk.