The Food and Drug Administration on Wednesday proposed requiring mammogram providers to tell women with dense breast tissue that the condition could make it harder to interpret their screening tests and to recommend that they talk with their physicians about whether they should have additional tests to check for cancer.

More than three dozen states have laws requiring that women who have mammograms be informed if they have dense breasts, but the language differs widely. The FDA proposal would establish a minimum standard that would apply nationwide, but states could retain more stringent requirements if they wished.

Dense breasts have relatively high amounts of glandular tissue and fibrous connective tissue and relatively low amounts of fatty tissue, according to the National Cancer Institute. Nearly half of women ages 40 and older who get mammograms are found to have dense breasts. Because such tissue appears white on a mammogram — as cancer does — it can obscure malignancies. In addition, dense breasts raise a woman’s risk of developing breast cancer, the NCI says.

After skin cancer, breast cancer is the most common cancer in women. About 268,000 women will receive diagnoses of invasive breast cancer in 2019, according to estimates by the American Cancer Society. More than 41,000 will die of the disease.

Joseph Cappello, whose late wife, Nancy Cappello, led a nationwide push for women to be notified about having dense breasts, called the FDA move “fantastic.” His wife’s late-stage breast cancer was diagnosed in 2004 after years of “normal” mammograms, he said. A physician told her that the cancer had been masked by other tissue. She and her husband founded the group Are You Dense? to press for breast-density education. She died in November of complications from cancer treatment.

Molly Guthrie, director of public policy and advocacy at Susan G. Komen, a breast cancer advocacy group, also welcomed the proposal, saying it was years overdue. Moving to a uniform standard is important because some state laws require notification about breast density but don’t tell women what to do next, “and that creates a lot of fear and confusion,” she said.

Amy Abernethy, the FDA’s principal deputy commissioner, said the proposal would “empower” patients by giving them more information to discuss with their physician. The information about breast density would be included in the summary letter mammography providers send to patients, as well as in the full report sent to physicians.

Jeffrey Shuren, director of the agency’s device center, said the proposed language would tell women they have dense breasts. And it would say that although mammography is the best screening test for breast cancer, it doesn’t find all malignancies, and that some patients might need additional screening.

Some women who have dense breasts could benefit from supplemental tests such as MRIs or ultrasounds, experts say. But that opinion isn’t unanimous. The U.S. Preventive Services Task Force, an independent panel of experts who review evidence on the effectiveness of preventive services, has concluded that there isn’t enough evidence to determine whether the benefits of extra testing outweigh the potential harm.

The FDA proposal, which will be open for public comment for 90 days, would update regulations issued under the 1992 Mammography Quality Standards Act, which authorized federal oversight of the more than 8,700 mammography facilities in the United States. Those rules involve the accreditation and certification of the facilities, as well as annual inspections and enforcement of quality rules.

The proposal would incorporate advances such as 3-D digital screening tools, officials said. It also would allow the agency to directly notify patients and their health-care providers if a mammography provider did not meet quality standards and a repeat test might be needed.

The topic of breast density has generated keen interest on Capitol Hill, with Sen. Dianne Feinstein (D-Calif.) and Rep. Rosa L. DeLauro (D-Conn.) pushing for years for a federal requirement that mammography providers inform women about breast density. Funding legislation signed in February directed the FDA to develop such language, an effort that was already underway.

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