Oakland, Calif., October 5, 2004--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 study in the October 6th issue of the Journal of the National Cancer Institute. Conducted by researchers from Kaiser Permanente’s Division of Research, Northern California, and from the National Surgical Adjuvant Breast and Bowel Project (NSABP), this is the first study to examine the potential connection between highly dense breasts and risk of second breast cancer after DCIS.
Women with DCIS--a noninvasive cancer in which malignant-appearing cells are contained within the 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-fold greater risk of a first 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’s Division of Research in Oakland, Calif., and colleagues studied 504 women (mostly 50 years or older) from the NSABP B-17 trial who had DCIS. The researchers examined the mammograms taken when the women were diagnosed with DCIS and then calculated the risk of subsequent breast cancer events.
While only approximately 7% of women studied had highly dense breasts--75% or more of their breasts composed of dense tissue--this group 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 composed of dense tissue). This increase in risk also was seen when second breast cancer events were restricted to invasive disease or when restricted to ipsilateral breast cancer (cancer in the same breast as the initial 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. Additional studies will be needed to confirm these findings and determine whether measures of breast density might aid in assessment of risk of a second breast cancer after DCIS. Dr. Habel is currently working on a second study to examine this potential link.