Dense Breasts Increase Cancer Recurrence Risk


Women who have been treated for breast cancer are at greater risk of cancer recurrence if they have dense breasts. The results of this new study follow previous research that indicated dense breast tissue increased a woman’s risk of breast cancer, but the theory had not been explored thoroughly.

It is not possible to determine how dense a woman’s breast is by looking at its size or shape; mammography or other imaging techniques are necessary to make that determination. Research indicates that breast tissue becomes less dense as women age, although it is not known exactly what causes density to develop. One theory is that a high-fat diet plays a significant role.


The new study, which was conducted by investigators at the Women’s College Research Institute in Toronto, involved a review of the medical records of 335 women who had undergone lumpectomy for breast cancer. The women were monitored for cancer recurrence with special attention paid to breast density as seen on mammography. The level of density was rated as low (less than 25% dense tissue present), intermediate (25 to 50%), and high (more than 50%).

Women who had the highest breast tissue density had a 21 percent chance that their breast cancer would recur over ten years. This compared with a 5 percent chance among women who were in the lowest category. The investigators also noted that the difference in cancer recurrence rates at ten years was more prominent in women who did not undergo radiation after their lumpectomy. In those women, 40 percent who had high density breast tissue had a return of their cancer compared with none of the patients who had low density breast tissue.

The results of this study can help clinicians and their breast cancer patients make treatment decisions based on breast tissue density. Women who have dense breast tissue may benefit significantly from electing radiation treatment after their lumpectomy.

Cil T et al. Cancer published online Nov. 9, 2009
Mayo Clinic