Publisher Health

In a long-awaited ruling, the Food and Drug Administration recommended on Thursday that all mammogram centers must tell women if they have dense breasts that could put them at increased risk for breast cancer.

The density of breast tissue — whether it contains mostly fatty or glandular tissues — varies from woman to woman and has nothing to do with the size or shape or feel of a woman’s breasts. The only way for a woman to know if she has dense breasts and, if so, how dense they are is by having a mammogram; she cannot tell by looking at or feeling her breasts.

Dense breast tissue may obscure cancer risks because it may be more difficult to spot small tumors with a mammogram.

Breast imagers divide density into four levels, designated A, B, C and D, ranging from almost entirely fatty breasts to extremely dense breasts. Only the 10 percent of women in level D, with extremely dense breasts, are at increased risk. Those in level C are at average risk for cancer, based on density alone.

The updated regulations require that patients simply be told that their breasts are dense or not dense; levels A and B would be “not dense,” while C and D are “dense.”

The F.D.A. will evaluate facilities to determine whether to award a certificate that verifies compliance with the new agency requirements. If a woman does not see a facility’s certificate, she can ask for it or check the F.D.A.’s website, Dr. Hilary Marston, the F.D.A.’s chief medical officer, said.

JoAnn Pushkin, the executive director of DenseBreast-info, Inc., an advocacy group, praised the agency’s update. Although 38 states have laws requiring mammography facilities to tell women whether their breasts are dense, those rules vary in how much information they require that women receive. Because the new regulations standardize what must be disclosed, she said, they “will lead to the earlier detection of breast cancer.”

But the situation with dense breasts and screening are not so straightforward, said Dr. Christoph Lee, a breast imager at Fred Hutchinson Cancer Center and director of the Northwest Screening and Cancer Outcomes Research Enterprise at the University of Washington. He fears the information women get about their breast density may be misleading.

Only a small minority of women with dense breasts are at increased risk for cancer based on breast density alone, Dr. Lee said, adding that “of all the clinical risk factors, breast density is only a moderate one.” Of much greater importance, he said, are risk factors like family history and previous breast cancer.

Dr. Marston of the F.D.A. said many doctors already get the more detailed information because many states require it to be reported. “Clinicians will have to decide on patients’ situation in terms of risk factors,” she said.

“The big question is: What do women do with the information?” Dr. Lee asked. If a woman is told her breasts are “dense,” what does that mean? Many women have heard — repeatedly — that if they have “dense” breasts, they need more frequent screening or extra screening with ultrasound or an M.R.I. If they get a report saying their breasts are ”dense” and their doctor says they need just regular mammograms, will they follow that guidance?

The F.D.A.’s hope is that the information — dense or not dense — will lead to a formal assessment by a doctor that can actually advise women if they are at overall higher risk.

But, Dr. Lee cautioned that an initial finding of breast density should not reflexively lead to more tests.

“It can be confusing for women to know what the next step should be,” he added. “There is some evidence from Europe that women in the top 10 percent of density could benefit from supplemental M.R.I. screening. But, he added, there is not much evidence that women outside of the extremely dense category would benefit from supplemental screening.

And even if women want such screening, insurers often will not cover it if a woman’s lifetime risk, according to standard risk calculators used by doctors, is less than 20 percent.

The new regulations, Dr. Lee said, “are a step toward informing women, but it is not clear where they will lead.”