Dense breasts raise risk of breast cancer

By Dr. Ananya Mandal, MDJul 27 2011

A new study supported by the National Cancer Institute found a higher cancer risk for women with dense breasts. It's the tissue in women's breast that can differ by heredity, from more fatty to more dense tissue. Fatty tissue shows up dark on a mammogram, but fibrous or dense tissue shows up white. So do small tumors, which can make them hard to find. The study was published in the July 27 online edition of the Journal of the National Cancer Institute.

“If you can imagine a white spot in the background of this dense white tissue, it can be hard to detect,” said Dr. Melissa Scheer from Manhattan Diagnostic Radiology. Researchers at Harvard also showed the tumors found in dense breasts are more aggressive. But it's the “masking effect” that could be the reason, says Dr. Elizabeth Morris of Memorial Sloan Kettering. “There could have been more aggressive tumors that developed just because it was more difficult to detect cancers in dense breasts,” Dr. Morris said.

“Our results suggest that breast density influences the risk of breast cancer subtypes by potentially different mechanisms,” wrote Rulla M. Tamimi, of Harvard Medical School and Brigham and Women's Hospital in Boston, and colleagues. “Further studies are warranted to explain underlying biological processes and elucidate the possible pathways from high breast density to the specific subtypes of breast carcinoma,” the authors added.

In 2009, Connecticut was the first state to pass a law mandating doctors to inform women of their density status after a mammogram. It's believed that that will give women more information to discuss with their doctor and when appropriate perhaps have ultrasound or other testing. New York, California and Texas are also now considering a law similar to Connecticut's in which doctors must inform women of their density status.

But there's a caution for women with dense breasts. “There are a lot of false positives with ultrasound,” Dr. Morris explained. “So it's not being recommended by any society currently, but on an individual basis it may be a good idea. So this is a conversation a woman should have with her physician. Even if a woman is told she has dense breasts in a mammogram, she should still have a mammogram every year,” Dr. Morris said.