Washington — All U.S. women getting mammograms would receive information about breast density, which can sometimes make cancer harder to spot, under a government proposal released Wednesday.

The Food and Drug Administration's proposed rules would standardize the information given to millions of women following scans to detect breast cancer. This is the agency's first proposed change to mammography standards in more than 20 years. Some states already require the notices.

More than half of women over age 40 have dense breasts, with less fatty tissue and more connective and glandular tissue. That tissue appears white on X-rays, the same color as growths in the breast, making mammograms harder to read. Dense breast tissue is one of the factors that can increase a woman's chances of developing cancer.

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"Breast cancer is one of the most worrisome health concerns facing women. The FDA plays a unique and meaningful role in the delivery of quality mammography to help patients get accurate screening to identify breast health problems early, when they can be effectively addressed," FDA Commissioner Scott Gottlieb, M.D., said in a statement.

Under the FDA's proposal, all women would receive a short summary about their breast density. For those with dense breasts, the letter would note that their tissue "makes it harder to find breast cancer," and could require additional testing. The letter would also recommend that they speak with a doctor about their "individual situation."

More than 35 states already require some kind of notification for dense breasts. But the FDA's proposal, if finalized, would apply to all states and set minimum standards for the information disclosed.

"We set a particular bar — you can't go below that bar — but states can impose more stringent requirements," said Dr. Jeffrey Shuren, the FDA's director for medical devices.

Regulators will take public comments for three months before finalizing the proposal, a process that can take months or sometimes years.

Professional guidelines don't specify next steps for women identified with dense breasts, but some physicians may recommend additional forms of scanning, including ultrasound or MRI.

Mammogram reports to doctors have long included information about density. But it wasn't routinely shared with women until some cancer survivors began pushing for disclosure laws. Congress gave the FDA authority to regulate standards for mammograms in 1992 and recently directed the agency to develop standard summary language.

Regulators said it was the first proposed update to national mammography standards in more than 20 years.

Other proposed regulations would: