A big downside of MRI for breast cancer screening: More cascade events

By Judith Garber | April 22, 2022

What’s the harm in using MRI for breast cancer screenings? As MRI has become a more popular screening tool for women at low or average risk of cancer, researchers caution that one MRI can easily “cascade” into more medical medical services and diagnoses, which leads to cause unnecessary harm and cost.

MRI screenings for breast cancer

Typically, breast cancer screening is done through mammography, which uses low-energy X-rays to detect masses or calcifications in the breast. Adding magnetic resonance imaging (MRI) screening for breast cancer has become more popular in recent years, because MRI is more likely to find cancers in women with dense breast tissue. However, even for women with dense breasts, MRI screening has not been shown to find more dangerous cancers, or to save more lives than mammography. (For more on why cancer screening does not necessarily save lives, check out these blogs.)

MRI screening also has significant downsides. For every 1000 women with dense breasts screened with MRI, 2.5 will find a cancer in between mammograms, but 80 will have a false positive result. Because of their high false positive rates and lack of proven benefit, MRIs for average-risk women are not recommended by specialty societies.

The risk of cascades

In a recent study in JAMA Network Open, Assistant Professor of Medicine at Harvard Medical School Dr. Ishani Ganguli and colleagues examined the prevalence of care cascades after breast MRI screenings. They compared patients who received MRIs with those who received mammograms, using a method to “match” patients in the two groups by age, health conditions, medical history, and other variables.

The authors found that patients who received MRIs for screening were more likely to have cascade events compared to those who had mammograms. For every 1000 patients who received a MRI, there were 50 additional imaging tests, 173 procedures, 130 visits, 30 diagnoses and 3 hospitalizations related to a cascade. For every 1000 patients with MRIs there were also 158 more doctor’s visits for incidental findings not related to breast cancer.

Patients who received an MRI incurred $1404 more in total costs and $31 more in out-of-pocket costs. That may not sound like much, but if the 50 million+ women of screening age all got MRIs instead of mammograms, there would be more than $57 million in extra costs, without any evidence of benefit.

A concerning trend

Currently, 38 states have legislation mandating that women be notified about breast density in some way, and more than ten require insurers to cover additional screening for women with dense breasts. These policies, paired with media hype around MRI for screening, will likely lead to even more breast MRIs, despite the lack of evidence that any more lives are saved compared with mammography.

The makers of imaging technology, who fund breast density advocacy efforts like DenseBreast-info.org, have a lot to gain from increased MRI screening — much more than we stand to gain by screening more low-risk women for breast cancer with MRI.

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