Supplemental Screening for Dense Breasts

This page is for people told after a mammogram that they have dense breasts. It explains what that means and what the evidence says about extra imaging.

Since September 10, 2024, the FDA requires every mammography facility in the US to tell you whether your breasts are dense. The wording is standard. If yours are dense, the letter says that dense tissue "makes it harder to find breast cancer on a mammogram and also raises the risk of developing breast cancer." It adds that in some people other imaging tests may help.

That letter is a notification, not a recommendation. It stops short of telling you what to do, because the evidence stops short too.

Radiologists sort breast tissue into four categories:

• Almost entirely fatty — about 10% of women
• Scattered areas of fibroglandular density (milk glands, ducts and supporting tissue) — about 40%
• Heterogeneously dense — about 40%
• Extremely dense — about 10%

These figures come from the National Cancer Institute’s “Answers to Commonly Asked Questions.”

The last two count as "dense." So roughly half of women who have mammograms are told they have dense breasts. It is not a disease. It is not something you caused. It is not something you can change. Density tends to decrease with age.

1. It masks. Dense tissue and tumors both appear white on a mammogram, so cancer is more likely to be missed.
2. It raises risk, modestly, and independently of the masking effect.

Hold one more fact alongside those. After accounting for other health factors, people diagnosed with breast cancer who have dense breasts are no more likely to die of breast cancer than those with fatty breasts.

The clearest evidence is the Dutch DENSE trial. It randomly assigned 40,373 women aged 50 to 75 who had extremely dense breasts and a normal mammogram.

• Interval cancers — those found between screening rounds — fell from 5.0 to 2.5 per 1,000 screenings in the group invited to MRI.
• Among women who actually had the MRI, it detected 16.5 cancers per 1,000 screenings.
• The false-positive rate was 79.8 per 1,000 MRIs. Of the biopsies MRI prompted, about 26% found cancer — meaning roughly three in four did not.

That is the trade-off in short. More cancers found earlier. Also many more false alarms, extra appointments and benign biopsies. The trial's main result was fewer interval cancers. The USPSTF says there is not enough research on health outcomes to know whether supplemental imaging helps.

• The USPSTF concluded the evidence is insufficient to recommend for or against supplemental ultrasound or MRI, regardless of density.
• The American Cancer Society says there is not enough evidence to recommend for or against yearly MRI for women whose only risk factor is extremely or heterogeneously dense breasts.
• The NCI cites the USPSTF: there is not yet enough evidence to recommend for or against extra imaging such as ultrasound or MRI.

Other professional groups may word their advice differently. This page did not check them, so ask your care team what they follow.

Whether supplemental imaging makes sense for you depends on more than density. Family history counts. So do known inherited variants such as BRCA1 or BRCA2, and chest radiation before age 30. So does your overall estimated lifetime risk. ACS recommends yearly MRI alongside mammography for people with a lifetime risk of 20% or higher, and that rests on risk, not on density alone.

One last practical point. Coverage for extra imaging can vary, so ask what it will cost before you schedule.

• FDA — Final Rule to Amend the Mammography Quality Standards Act (breast density notification)
• Supplemental MRI Screening for Women with Extremely Dense Breast Tissue (DENSE trial, NEJM 2019)
• USPSTF — Breast Cancer: Screening (2024)
• American Cancer Society — Recommendations for the Early Detection of Breast Cancer