Should breast cancer survivors be screened by MRI?

This new study is the largest and most comprehensive to date, according to lead researcher Karen Wernli of the Kaiser Permanente Institute for Health Research in Washington, WA.

Wernli and her colleagues screened information from more than 13,000 breast cancer survivors who had been screened for breast cancer at multiple sites in the United States. In total, they received nearly 34,000 mammograms and approximately 2,500 MRI exams between 2005 and 2012.

Overall, MRI detected more tumors – at a rate of 11 per 1,000 exams, compared to 8 per 1,000 for mammography alone. To reach this rate, however, the MRI group had to undergo more biopsies: 10% of these screenings led to a biopsy, compared to 4% of the mammograms.

And although MRI has detected more early tumors, the ultimate benefit is not clear: the rate of "interval" cancers – cancers diagnosed in the year between screenings – was the same in the mammography and MRI groups alone.

This suggests, according to Wernli, that mammography detects "clinically important" tumors as well as MRI – small tumors that will progress sufficiently to produce symptoms (like a lump) next year.

Wernli pointed to the broader potential impact of using MRI screening on all women with a history of breast cancer. If every American woman diagnosed with non-advanced breast cancer in 2018 underwent MRI, there would be more than 14,000 additional biopsies.

However, for some patients, these types of numbers may not mean much, said Newell. If, for example, a woman is very anxious about recurrence of cancer, she might feel that the chances of having a biopsy are worth it.

The decision is up to women to discuss the advantages and disadvantages of MRI scans with their doctors, the experts said.

They also agreed that more research is needed to determine whether MRI screening is more beneficial to some breast cancer survivors than to others.

Smith gave some examples. It may be that women whose breast tissue is dense – which may complicate the interpretation of mammography – benefit more from the addition of MRI. The same could be true of women with a family history of breast cancer.