MRIs May Detect Cancer in Dense Breasts Better Than Mammograms—Should You Get One?

Magnetic resonance imaging (MRI) is the most precise way to screen for breast cancer in people with dense breasts, new research found.

The Centers for Disease Control and Prevention (CDC) estimates around 264,000 women are diagnosed with breast cancer every year, and the earlier it’s caught, the more likely a woman is to survive. Earlier diagnoses also often require less aggressive treatment.

Early detection starts with regular, accurate screening.

Mammograms are still considered the gold standard for breast cancer screening, but the images only detect cancer about 85% of the time, said Larry Norton, MD, medical director of the Evelyn H. Lauder Breast Center at the Memorial Sloan Kettering Cancer Center in New York—he was not involved in the aforementioned study.

This can be a big issue for the roughly 50% of the population who have dense breasts, which means the breast is composed of a higher amount of fibrous or glandular tissue compared to fatty tissue. Compared to breasts that have more fatty tissue, dense breasts create more white areas on a mammogram image—the same color as tumors. For that reason, it’s recommended that people with dense breasts receive supplemental breast cancer screening following every mammogram.

“As the breast density increases, the ability of the mammogram to detect breast cancer decreases, and you may have a false negative mammogram,” explained the new study’s lead author, Vivianne Freitas, MD, an assistant professor at the University Health Network in Toronto, Ontario, and staff of the Joint Department of Medical Imaging, Breast Division at the University of Toronto.

MRIs Outperformed Other Tools

To determine imaging effectiveness, Dr. Freitas and her colleagues analyzed 22 studies that together included more than 260,000 patients who had been screened for breast cancer. Of those, about 132,000 who had dense breasts also had a negative mammogram. They found that mammograms missed 541 cancers that were later detected with other means of screening, including MRI, ultrasounds, and a detailed imaging technique called digital breast tomosynthesis.

The study found that while three types of non-MRI screening methods detected cancer at the same rates, MRI outperformed all three when detecting cancer in dense breasts. 

Yet there is one obstacle that may prevent MRI from becoming a common breast cancer screening tool—the scan is extremely expensive and therefore is not a realistic choice for mass screening.

“In the U.S. the most common supplemental screening modality when the patient has dense breasts is ultrasound because they are both available and low cost,” noted Dr. Freitas. 

While ultrasounds have been shown to be better than a mammogram at detecting breast cancer in dense breasts, the study went on to show that the imaging is not the absolute best. 

“MRI is a better tool for finding small cancer, particularly in difficult-to-examine breasts,” said Dr. Norton, noting that small cancer can often be detected through changes in blood vessels that deliver nutrients to the tumor, rather than the appearance of an actual tumor on a scan. 

Alternative Imaging Options

MRIs are incredibly sensitive, but alternative imaging techniques, including a contrast-enhanced mammogram, which uses dye to make it easier to see tumors on the scans, could provide cheaper alternatives that are better at detecting cancer in dense breasts compared to traditional mammograms. Dr. Norton said a minimal exposure MRI can still do a good job at detecting cancer—and at a lower cost. 

In 2019, Congress passed legislation that requires healthcare professionals to inform a woman if she has dense breasts. This information is available after a mammogram—it cannot be done by feel. But even if dense breasts are confirmed, it may be tricky to find suitable payment options for additional imaging.

According to Megan Kalambo, MD, an associate professor in the Department of Breast Imaging at The University of Texas MD Anderson Cancer Center in Houston, most insurance companies still do not currently cover MRI for breast cancer screening in people with dense breasts. 

“Even if we are making recommendations for supplemental screening with MRI, that cost will end up coming out of pocket unless we develop new guidelines with insurance companies,” Dr. Kalambo told Health. 

Mammograms Still Come First

The American College of Obstetricians and Gynecologists recommends women who have an average risk for developing breast cancer get a mammogram every 1–2 years starting at age 40.

According to Dr. Freitas, people with dense breasts should still get regular mammograms in addition to supplemental screening. While future research may show different results, mammograms are still the only method of breast cancer screening that has been shown by clinical trial research to decrease breast cancer mortality. 

“There have not been any large-scale trials in the past 40 years, but when we are looking at screening large populations for preventative care, we want to make sure that tool is readily available and at low cost,” said Dr. Kalambo, noting that MRI is neither, and also requires contrast dye, which some patients may be allergic to. “That’s why it isn’t considered the gold standard test at this time.”