State laws requiring women with dense breasts to be told about the benefits of further imaging after mammography may not lead more women to get extra screening, a U.S. study suggests.

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.

“Dense breasts may mask small cancers on mammography,” said Dr. Christoph Lee, senior author of the study and a researcher at the University of Washington and the Hutchinson Institute for Cancer Outcomes Research in Seattle.

“Ultrasound is not influenced by breast density and may detect additional cancers,” Lee said by email.

To see whether dense breast notification laws changed how often physicians ordered screening ultrasounds for women, researchers examined data from 12,787 wellness visits from 2007 to 2015 by women 40 to 74 years old.

Overall, about 29% of the women had breast exams during their checkups and 22% had a screening mammogram ordered, but just 3.3% had screening ultrasounds ordered.

Screening ultrasound rates remained persistently low throughout the study period, and didn’t change after states passed dense breast notification laws, which were on the books in 36 states as of January 2019.

“Physicians may not recommend supplemental ultrasound for the majority of women with dense breasts as the current evidence suggests that risks outweigh benefits of screening ultrasound,” Lee said.

With ultrasound screening, more women with tumors may detect the cancer sooner, when it’s easier to treat, and early detection is the motivation behind many state laws recommending dense breast notification. But there is also a risk of so-called over-diagnosis, which can cause women to undergo needless testing or treatments for relatively harmless tumors.

It’s possible some doctors and patients discuss screening ultrasounds and decide the risks aren’t worth it, Lee said. It’s also possible that physicians don’t order ultrasounds because there isn’t a nearby radiology facility that can do these tests or because insurance may not cover it.

One limitation of the study is that researchers lacked data on how many women got ultrasound screening, since the focus was on whether physicians ordered the test, not whether women followed through.

A previous study of dense breast notification laws found that more women did get screening ultrasounds when the laws required patients to be told about the benefits of additional tests like ultrasounds or MRIs.

In the current study, however, notification on its own didn’t appear to boost ultrasound screening rates.

It’s possible this study found no change in ultrasound screening after dense-breast-notification laws passed because some physicians recommended MRIs instead, said Dr. Richard Bleicher, leader of the breast cancer program at Fox Chase Cancer Center in Philadelphia.

“Breast MRIs are recommended and used frequently in women who have a genetic predisposition for breast cancer; these women are those who have a family history and get screened at a young age for a gene mutation, or develop cancer at a young age and then get gene tested,” Bleicher, who wasn’t involved in the study, said by email.

“Since MRIs are the predominant modality used (in addition) to mammography in these younger women, these are the same women who typically have the densest breasts, and screening ultrasound is unlikely to replace breast MRI,” Bleicher said.

SOURCE: bit.ly/2KpkX5X Journal of the American College of Radiology, online July 18, 2019.