MRI scans are better at detecting breast cancer at its earliest stage, say researchers in a study in The Lancet. But at least one Canadian expert says it is unlikely that MRI will ever be used routinely as a breast cancer screening tool.
The study by Dr. Christiane Kuhl, a radiologist at the University of Bonn, found that magnetic resonance imaging was better than standard mammograms at detecting a non-malignant tumour called "ductal carcinoma in-situ," or DCIS.
Almost all malignant breast cancer is believed to start out as DCIS, which are non-invasive cancerous cells in the milk ducts.
Kuhl and colleagues studied 7,319 women who either had breast cancer or had a family history of cancer. Over five years, 167 women were diagnosed with DCIS; 92 per cent of cases were picked up through an MRI and only 56 per cent by mammogram.
In women who had the most severe cases of DCIS -- those most likely to lead to a diagnosis of breast cancer -- MRI picked up on 98 per cent of cases, mammography only 52 per cent.
Kuhl's team says their findings suggest that MRI could improve the ability to diagnose DCIS and suggest that it should become a standard screening tool.
"MRI should thus no longer be regarded as an adjunct to mammography but as a distinct method to detect breast cancer at its earliest stage," they write.
But Dr. Ellen Warner, a medical oncologist at Sunnybrook Health Sciences Centre in Toronto says that's not likely to happen.
"We're never going to use MRI routinely," she told . "It's just not logical."
She notes that MRIs are used routinely for patients considered at high risk of breast cancer, such as those with a family history and key genetic markers. But the diagnostic tool is expensive and picks up "lots and lots" of false positives.
Those patients wrongly identified often have to undergo unnecessary and painful biopsies and follow-up, sometimes all for nothing. What's more, having an MRI does not save women from undergoing the uncomfortable mammogram process, as MRIs are always done alongside mammograms.
She says detecting more cases of DCIS does not necessarily mean that doctors would be able to prevent more breast cancer deaths.
"A 10-mm DCIS may not become invasive and lead to cancer, whereas a 1-mm might," she says. "There are a lot of other factors at play."
There are better diagnostic technologies becoming available, Warren says, such as digital mammography, which is improving breast imaging and becoming more widely adopted across Canada.
Another tool that is still at the experimental stage is called breast tomosynthesis, which takes a series of images that are mathematically processed into a series of one millimeter slices that show the tissue structure in three dimensions.
