In this study, breast cancer patients with dense breasts who were treated with lumpectomy were found to have a much higher rate of cancer recurrence in the breast (local disease recurrence) than patients with low breast density. Women with the most dense breasts had a 21 percent chance of local cancer recurrence whereas women with low breast density had a 5 percent chance. Radiation treatment was found to be important for women with dense breasts. For women who did not receive radiation therapy, 40% in the high-density category had experienced local breast cancer recurrence by the 10-year mark whereas none of the women with low breast density had a recurrence.

Dense breasts and breast cancer treatment

While the study headline is that women with dense breasts have a higher risk of recurrence, perhaps the most important message of this study is the value of radiation treatment for women with dense breasts who undergo a lumpectomy to remove early-stage breast cancer. It makes sense that an environment susceptible to the development of breast cancer (in this case, dense breast tissue) would be more likely to generate new breast tumors over time. Radiation treatment appears to offer significant protection against breast cancer recurrence to such women. Whether both breasts should be irradiated when cancer is found in one of them is an open question.

Breast density changes over time and as a result of related events such as pregnancy. This suggests that breast density might be influenced by environmental and lifestyle factors. In fact, red meat consumption has been found to be associated with dense breasts whereas intake of vitamin D in combination with calcium is associated with lower breast density.