Supplemental MRI of Very Dense Breast Tissue Finds Early Cancers, at Higher Risk of False Positives

A recent study published in The New England Journal of Medicine says that women with dense breast tissue who undergo supplemental magnetic resonance imaging (MRI) tests have lower rates of interval cancers than those who receive only mammography tests.¹

Researchers looked at data from 40,373 women in the Netherlands with extremely dense breast tissue in a multicenter, randomized, controlled trial.

All of the women were between the ages 50 and 75 and received negative results on their last mammography test. Of that total, 32,312 received mammography screening only, while of the 8061 invited to participate, 4783 underwent supplemental MRI screening only.

After 2 years, researchers followed up with patients in both groups and found the interval cancer rate in the MRI-intervention group to be 2.5 per 1000 screenings. In the mammography-only group, the rate of interval cancer was 5 per 1000, a difference of 2.5 per 1000 screenings. Interval cancers are defined as “all the breast cancers that were diagnosed after negative results on mammography before the next scheduled mammography examination.”

These findings are significant because women with extremely dense breast tissue have a higher risk of breast cancer compared with those with fattier breast tissue.

According to The New York Times, “Just under half of women over the age of 40 have dense breasts, which means their breasts have more connective and fibrous tissue than usual, and relatively less fat.” Both tissue and tumors show up white on a mammogram, while fat shows up black, making it easier to spot tumors in fattier tissue.²

Researchers are hoping the study is the first in a series of steps to improve health outcomes for women with dense breast tissue.

“The first indication for a reduction in morbidity and mortality is a reduction in the incidence of interval cancers, since such a reduction may mean that cancers that would otherwise have become symptomatic would now be detected earlier,” they said.

The study also indicated that MRI examinations sped up the time of diagnosis. During follow-up mammography screenings cancer-detection rates were as follows:

• 2.0 per 1000 mammography screenings among MRI participants
• 7.1 per 1000 screenings among the MRI non-participants
• 6.0 per 1000 screenings among the women in the mammography-only group

The MRI screening cohort did have a high false positive rate of 79.8 per 1000 screenings. However, researchers said this would be addressed in future studies by measures such as computer-aided diagnoses, radiomics and deep-learning methods.

However, an accompanying editorial noted that "The ultimate test of the value of MRI screening in women with extremely dense breast tissue will be whether its use improves survival—an answer that we will not have for a very long time," and questioned whether women will have an increased risk of biopsies that do not contibute to survival.

References

1. Bakker MF, de Lange SV, Pijnappel RM, et al. Supplemental MRI screening for women with extremely dense breast tissue. N Engl J Med. 2019;381(22):2091-2102. doi:10.1056/NEJMoa1903986.

2. Rabin RC. M.R.I.s can better detect cancer in women with dense breasts, study finds. The New York Times. November 27, 2019. nytimes.com/2019/11/27/health/dense-breasts-MRI-cancer.html?. Accessed December 9, 2019.

3. Longo DL. Detecting breast cancer in women with dense breasts. N Engl J Med. 2019;381(22):2169-2170. doi: 10.1056/NEJMe1912943.