Having highly dense breasts may be associated with an increased risk of a second breast cancer among women who have had a ductal carcinoma in situ (DCIS), according to a new study.

Women with DCIS-a noninvasive condition in which abnormal malignant-appearing cells are found in the lining of a breast duct-have a substantially increased risk of a second breast cancer, but few predictors of this risk have been identified. Having extensive areas of breast tissue that appear dense on mammograms has been associated with a four to six times greater risk of primary breast cancer compared with women who have small or no areas of dense breast tissue.

To see if breast density was related to the risk of getting a second breast cancer after DCIS, Laurel A. Habel, Ph.D., of Kaiser Permanente Medical Care Program in Oakland, Calif., and colleagues studied 504 women from the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-17 trial who had DCIS. They examined the mammograms taken when the women were diagnosed with DCIS and then calculated the risk of subsequent breast cancer events.

While only about 7% of the women had highly dense breasts-75% or more of their breasts were composed of dense tissue-they had 2.8 times the risk of subsequent breast cancer (DCIS or invasive) compared with women who had the least dense breasts-less than 25% of their breasts were composed of dense tissue. In addition, women with dense breasts also had 3.2 times the risk of invasive breast cancer and 3.0 times the risk of any ipsilateral breast cancer (cancer in the same breast as the DCIS).

The authors suggest that breast density may reflect the activity of hormones and other growth factors. In addition, breast density may affect the accuracy of disease surveillance through mammography and clinical breast examination after treatment for DCIS.

SOURCE:
Journal of the National Cancer Institute, October 6, 2004