Dense Breasts and Cancer Screening

Although the age a woman should first get a mammogram has been debated, the issue of breast density is increasingly receiving attention as states are passing legislation that requires healthcare providers to notify women of this condition.

Aggressive grassroots efforts pushed through laws in California, New York and Virginia this year. Texas and Connecticut approved breast density legislation in prior years, and there are similar laws pending in Congress and in about a dozen other states. The organization AreYouDense.org offers information about the issue and has been a proponent of these efforts.

About 10 percent of women have extremely dense breasts, according to the American College of Radiology, while 10 percent have almost entirely fatty breast tissue. The remaining 80 percent fit into one of two middle categories on a 1-to-4 density rating scale known as BIRADS (Breast Imaging Reporting and Data System).

Women with the highest density are four to five times more likely to develop breast cancer than women at the lowest extreme whose breast tissue is mostly fat, says Carol Lee, MD, a diagnostic radiologist at Memorial Sloan-Kettering Cancer Center in New York. These women, however, do not appear to be more likely to die from the disease than others with breast cancer, according to a 2012 study in the Journal of the National Cancer Institute.

“Fatty tissue isn’t breast cells, although it may be in the breast,” explains Stacey Vitiello, MD, a radiologist specializing in breast imaging and biopsy at Montclair Breast Center in Montclair, N.J. “The more fatty tissue is in the breast, the less real estate there is to develop cancer in. Dense breasts have more ‘active’ breast tissue specific to breasts where cancer forms.”

Still, there’s no consensus among experts on how to manage patients with high breast density.

Lee says any woman can ask her radiologist for her BIRADS density score, but she “can’t tell on her own if she has dense breasts, no matter what they may feel like. There’s no other way to know [other] than having a mammogram.”

Dense breasts contain more fibrous and glandular tissue—which appears white on mammograms, just like cancers—while fatty tissue shows up as gray or black. Lee says women should know if they have dense breasts because a normal reading on a mammogram could be misleading. “They [may] want to take their screening to the next level and have an ultrasound or, if they’re at high risk for other reasons, an MRI,” she says.

The ability of ultrasound and magnetic resonance imaging (MRI) scans to pick up cancer is not as adversely affected by breast density as is mammography, making them more effective, especially when combined with a mammogram.

But ultrasound produces a high percentage of false-positive results leading to unnecessary biopsies, Lee notes. MRI scans, which catch more cancers than mammography or ultrasound, also have a higher false-positive rate. Either technique, if recommended, would be paired with mammography and not act as a replacement.

Both Vitiello and Lee agree that unless women with dense breasts have other risk factors for breast cancer, such as a strong family history, they should be screened similarly to average-risk women.

Prevention with selective estrogen receptor modulators (SERMs), often prescribed for women with estrogen-positive breast cancers, may be too aggressive a tactic for those whose only risk factor for the disease is dense breasts.

“There’s no evidence that putting people on [estrogen blockers such as] tamoxifen because of dense breasts is a reasonable thing to do, and certainly not screening earlier, either,” Lee says.

Women with dense breasts who’ve already had breast cancer are at greater risk of receiving a cancer diagnosis in the opposite breast after a lumpectomy for ductal carcinoma in situ, according to a study in Cancer Epidemiology Biomarkers & Prevention. But Vitiello recommends annual breast MRIs for breast cancer survivors regardless of breast density. The current standard for breast cancer survivors is mammography.