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Right now, experts recommend that breast cancer survivors have yearly mammograms to help catch any recurrences early. An unresolved question is whether adding breast MRI to that screening is beneficial.
In the new study, researchers found that when survivors underwent MRI screening, it did tend to detect more tumors, compared to yearly mammography alone. But it also more than doubled the number of biopsies women needed -- many of which turned out to be benign.
Experts said it leaves women with a choice to make.
"Rather than deciding for women that the risks of any exam outweigh the benefits, we need to be clear and open about exactly what those risks and benefits are, and let them decide what's most important to them," said Dr. Mary Newell, a radiologist at Emory University's Winship Cancer Institute in Atlanta.
Newell wrote an editorial accompanying the study published online June 4 in the journal Radiology.
Because of that, MRI is reserved for women at high risk of breast cancer. (The average U.S. woman has about a 12% risk.) Right now, the ACS recommends MRI, along with yearly mammograms, when women have a roughly 20% or higher lifetime risk of breast cancer.
But it does not include women with a personal history of breast cancer.
That's because at the time the recommendations were made -- in 2007 -- "there simply weren't any good studies from which we could draw conclusions," said Robert Smith, vice-president of cancer screening for the ACS.
Even now, he said, there remains little research evidence.
The new study is the largest and most comprehensive to look at the issue so far, according to lead researcher Karen Wernli of Kaiser Permanente Washington Health Research Institute in Seattle.
Wernli and her colleagues combed through information on more than 13,000 breast cancer survivors who were screened for breast cancer at several sites across the United States. All together, they had received nearly 34,000 mammograms and about 2,500 MRI screenings between 2005 and 2012.
Overall, MRI caught more tumors -- at a rate of 11 per 1,000 exams, compared to eight per 1,000 for mammography alone. To achieve that rate, though, the MRI group had to undergo more biopsies: 10% of those screenings led to a biopsy, compared to 4% of mammograms.
And while MRI detected more early tumors, it's not clear what the ultimate benefit is: The rate of "interval" cancers -- cancers diagnosed in the year between screenings -- was the same in the mammography-only and MRI groups.
That suggests, according to Wernli, that mammography did about as well as MRI in detecting tumors that were "clinically important" -- small tumors that would progress enough to produce symptoms (like a lump) in the next year.
Wernli pointed to the potential broader impact of using MRI screening for all women with a history of breast cancer. If every U.S. woman diagnosed with non-advanced breast cancer in 2018 underwent one MRI, there would be more than 14,000 additional biopsies.
For individual patients, however, those types of figures may not mean much, Newell pointed out. If, she said, a woman has a lot of anxiety about a cancer recurrence, for example, she might feel the higher odds of needing a biopsy are worth it.
The decision comes down to women discussing the pros and cons of MRI screening with their doctors, the experts said.
They also agreed that more research is needed to figure out whether MRI screening benefits certain breast cancer survivors more than others.
Smith pointed to some examples. It might be that women with dense breast tissue -- which can make mammography interpretation harder -- benefit more from adding MRI. The same could be true of women with a family history of breast cancer.
But studies are needed to find out, Smith said.
There are also practical issues. Breast MRI costs substantially more than mammography, and the ACS advises women to first check that their insurance plan covers it.
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