By Lisa Rapaport

(Reuters Health) – State laws requiring women with dense breasts to be told about the benefits of following up a mammogram with further tests are associated with higher rates of additional screening and more diagnoses for breast cancer, a U.S. study finds.

Laws that only require women to be told they have dense breasts, without any further information, don’t seem to make a difference in extra screenings or cancers detected, the study team reports in American Journal of Public Health.

Roughly half of U.S. women in their 40s and 50s have dense breast tissue, which increases their risk of breast cancer and makes it harder to detect tumors with mammography. Several states require healthcare providers to send notification letters to women whose mammograms show dense breast tissue. Some states also require that these higher-risk women be advised to get screened with ultrasound or MRI, which can better detect tumors in dense breast tissue.

A new proposal from the U.S. Food and Drug Administration, announced March 27, would require all mammography facilities in the U.S. to include breast density information in letters to patients. The FDA says it is proposing “specific language that would explain how breast density can influence the accuracy of mammography,” but the agency’s announcement does not say the letters must advise about further testing options.

For the current study, researchers examined data on screening and cancer diagnoses for more than 1.4 million women ages 40 to 59 in nine states with dense breast notification laws and 25 states without these laws.

“We found that dense breast notification laws were associated with small increases in cancer detection,” said lead study author Susan Busch of the Yale School of Public Health in New Haven, Connecticut.

“This effect was only found in states with laws that included language about the benefits of supplemental testing,” Busch said by email. “We did not have enough follow-up data to take the next step and determine whether dense breast notification laws were associated with reduced breast cancer mortality.”

The goal of mammograms is to detect tumors before they can be felt in a physical breast exam, catching cancer sooner when it’s easier to treat. Ideally, this should mean fewer women are diagnosed when tumors are more advanced.

It’s not clear from the current study to what extent dense breast notification laws might lead to so-called over-diagnosis, which can cause women to undergo needless testing or treatments for relatively harmless tumors; it’s also not clear how many lives might be saved by catching aggressive cancers sooner when they’re easier to treat.

Very few women in the study got recommended ultrasounds after screening mammograms found dense breast tissue, even though insurance covers these tests, the researchers note.

Women with dense breasts should continue to get mammograms and should also speak to their doctor to determine what screening plan is best for them, advised Dr. Catherine Tuite, chief of breast radiology at Fox Chase Cancer Center in Philadelphia.

“Mammography is still the gold standard for the detection of breast cancer, even for women with dense breasts, and multiple studies have proven that detection of cancers by mammography reduces the risk of death due to breast cancer for women starting at age 40,” Tuite, who wasn’t involved in the study, said by email.

“Women diagnosed with breast cancer who participate in screening mammography are less likely to die from breast cancer than those who do not,” Tuite added. “Supplemental screening tests such as screening whole breast ultrasound, MRI or MBI are not a substitute for mammography because there are still some cancers and precancerous changes that will show on a mammogram better than on other tests.”

SOURCE: American Journal of Public Health, online March 21, 2019.