Study suggests pros, cons for mammogram plus MRI scan

Giving women with very dense breasts an MRI scan with a mammogram led to fewer missed cancers but also to a lot of false alarms and treatments that might not have been needed, a study found.

The results give a clearer picture of the trade-offs involved in such testing, but they can’t answer the biggest question — whether using both saves lives.

For women with dense breasts trying to decide on screening, “the dilemma remains,” Dr. Dan Longo of the New England Journal of Medicine wrote in an editorial published with the study Wednesday.

About half of women over 40 have dense breasts, and about 10 percent have very dense ones. That raises their risk of developing cancer and makes it harder to spot on mammograms if they do. U.S. regulators are making rules to require that women get breast density information when they have mammograms. But what to do if a woman has dense breasts is unclear: It’s not known if more or different types of screening such as MRIs or ultrasounds help.

The study involved more than 40,000 Dutch women ages 50 to 75 with very dense breasts who had normal results from a mammogram, a screening X-ray offered every two years in the Netherlands. About 8,000 of them also were offered an MRI scan, which uses magnets to create detailed images, and 4,783 women agreed.

Researchers tracked how many breast cancers were detected in each group within two years. Finding more of these “interval cancers” implies that the initial screening might have missed them.

The rate of these cancers after two years was twice as high in the group that was only offered mammograms. That suggests adding MRIs to initial screening caught more cancers, but they also gave a lot of false alarms— about 80 per 1,000 scans. Three-quarters of women who had a biopsy after a questionable MRI turned out not to have cancer.

MRIs also led to more side effects during the scan or later testing. And they cost much more than mammograms.

Torin Halsey The Associated Press file A new study suggests that adding MRIs to mammograms to screen women with very dense breasts might find more cancers but also gives a lot of false alarms.