Dense Breasts May be Leading Risk Factor For Breast Cancer

Women whose breasts are composed mainly of dense glandular tissue rather than fat may have higher odds of developing breast cancer, a recent study suggests.

Researchers examined data on more than 18,000 women with breast malignancies and 184,000 women the same age without breast cancer. They found breast density appeared to be the biggest indicator of cancer risk, even more than other common risk factors like family history or waiting until after age 30 to have babies.

“Women with dense breasts have a roughly 2-fold higher breast cancer risk relative to women with non-dense breasts,” said lead study author Dr. Natalie Engmann of the University of California, San Francisco.

This is a problem because 60 percent of younger women have dense breasts and so do 40 percent of older women who have gone through menopause – and because dense breasts make tumors harder to detect on mammograms, Engmann said.

“Our findings suggest that because breast density is a strong, common risk factor that can be modified, reducing the number of women with dense breasts may prevent a substantial proportion of breast cancer cases,” Engmann.

In the study, online February 2 in JAMA Oncology, researchers examined data on women with four categories of breast density: almost entirely fat, mostly fat with some dense tissue, moderately dense and predominantly dense. Then, they looked at several known breast cancer risk factors: women’s weight, family history of the disease, personal history of benign biopsy results, breast density and having a first baby after age 30.

About 39 percent of breast cancer cases before menopause and 26 percent of cases afterwards might be prevented if women in the two highest breast-density categories had less dense breast tissue, the study team calculated.

It’s unclear that women can do anything to reduce breast density, but it may make sense for them to consider screening alternatives to mammograms, said Dr. Christine Berg, a NCI researcher who wasn’t involved in the study.

“I think it makes more sense for a woman with dense breasts, particularly with other risk factors, to discuss with her doctor and the radiologist whether or not she would benefit from other types of screening such as MRI,” Berg said by email. “Breast tomosynthesis is an emerging technology which I think is better than standard mammography.”

Berg also recommended a calculator (here: developed by the Breast Cancer Surveillance Consortium for women to assess their individual risk.

Bottom line: For women with dense breasts, the addition of alternate screening such as 3D bilateral whole breast ultrasound or MRI can improve the early detection of breast cancer.

About the author: Raja P. Reddy, MD is a board certified diagnostic radiologist specializing in breast imaging. He is also a contributing editor for Women’s Imaging Specialists, a leading provider of outpatient women’s imaging services in the greater Atlanta, GA area.