Understanding how dense breasts affects cancer risk remains a problem of standardization. No one method of measuring breast density has been agreed upon. More recently computerized image analysis has been incorporated to quantify dense breast tissue by measuring the area occupied by the entire breast tissue then measuring the dense area and calculating the percentage that is dense. Researchers also do not agree as to what causes women's breasts to be denser than others. Breast density may be a surrogate marker for proliferation of breast tissue, but it remains unclear whether it results from proliferation of stromal or epithelial cells.
Controversy exists over why breast density is an independent cancer risk.
Dense areas on mammography make cancer detection more difficult. Density of the breast tissue may be a marker of other factors, such as history of hormone exposure. But it is unclear whether current or past breast density serves as the better risk predictor. It has been shown by a preliminary study that tamoxifen reduced the breast density and risk of recurring cancer in women who had previously been treated for unilateral breast cancer. Whether the density reduction is concomitant or causative remains to be seen.