Dense breasts and cancer risk: What women need to know

After her mother’s death from aggressive breast cancer almost 10 years ago, Rosie Ybarra’s mammogram showed that she had dense breast tissue and fibrocystic breasts – prone to lumps.

Following cyst drainage on several worrisome but benign lumps, Ybarra did research to find a physician who would follow her closely and help set her mind at ease. Her research led her to MD Anderson.

Because of Ybarra’s family history and her dense breast tissue, which makes it more difficult to see cancer on a mammogram, her oncologist, Powel Brown, M.D., Ph.D., professor and chair of Clinical Cancer Prevention, put her on a yearly schedule in which she would have a mammogram and an ultrasound, alternating six months later with a breast MRI.

“When they did my ultrasound and mammogram in June 2018, the images were negative, and everything looked good," Ybarra says. “When I came back in December, they did an MRI of my breasts, and they picked up a suspicious spot.”

An MRI biopsy revealed lobular breast cancer, a rare form. This February, she underwent a double mastectomy – her left breast for treatment and her right breast as an elective preventive measure.

“I call Dr. Brown my angel because if we hadn’t been persistent and doing both the MRI and the ultrasound, the cancer would not have been picked up at that time. Women have to take charge of their own medical care and ask questions,” Ybarra says.

Risk factors

Having a close relative with breast cancer has long been known to increase a woman’s risk of breast cancer, along with age, certain genetic mutations and several other risk factors.

Density is not related to breast firmness, but to the way the tissue appears on a mammogram. Dense breasts have less fatty tissue, which appears dark on a mammogram, and more glandular tissue, which appears white. Dense breasts make it harder for mammograms to detect cancer, because cancer also appears white.

Several epidemiologic studies have shown that dense breasts also impose a higher risk of breast cancer. It’s estimated that about half of women who get mammograms have dense breasts. For most women, breasts become less dense with age.

In February 2019, a federal law passed requiring all mammography providers to notify patients if they have dense breasts and to tell them that breast density can hide cancer on a mammogram. The law also instructs mammography providers to advise patients to consult with their doctors. Thirty states already have similar laws, but the federal legislation will standardize the requirement and the notification’s wording throughout the country.

Screenings

Regular mammograms are still the best way to find breast cancer early. In the U.S., an annual screening mammogram is recommended for women who are 40 or older.

“That is the only test that has been shown to decrease the mortality of breast cancer,” says Marion Scoggins, M.D., associate professor of Diagnostic Radiology-Breast Imaging.

Most centers now use digital mammography, rather than film, because radiologists can fine-tune the digital electronic images so that tiny abnormalities stand out better. A more recent improvement is 3D mammography, called tomosynthesis. The procedure is the same as for 2D mammography, but tomosynthesis improves detection of breast cancer with fewer false positives.

“We’ve been educating our patients at MD Anderson about the availability of tomosynthesis for many years. Tomosynthesis is really a better mammogram for all women, and it does not require a doctor’s order,” Scoggins says.

If a woman’s breast tissue is dense on mammography, a breast ultrasound is the most common test recommended in addition to a mammogram. Ultrasound is an inexpensive test that does not expose a woman to radiation.

A breast MRI currently is recommended only for women at high risk. Until further data become available, there is not sufficient scientific evidence to recommend MRI screening for average-risk women.

Clinical trial

At MD Anderson and four other U.S. sites, a clinical trial is testing  whether a tamoxifen gel, applied once a day for a year, rather than ingesting tablets, can reduce breast density and the risk of breast cancer.

“The tamoxifen tablet is the only Food and Drug Administration-approved agent for breast cancer prevention, but because of concerns for side effects, a number of high-risk women don't feel comfortable taking it,” says Banu Arun, M.D., the clinical trial’s principal investigator and MD Anderson professor of Breast Medical Oncology. “The gel, which, in preliminary findings, is associated with minimal side effects, could be an exciting alternative.