Aug. 9, 2007 -- MRI screening has been considered less sensitive than mammography for detecting precancerous cells in the breast which are confined to the milk ducts, but a new study suggests the opposite is true.
Breast MRI detected 92% of surgically confirmed cases of ductal carcinoma in situ (DCIS) in the German study, compared to a 56% detection rate for mammography. Because DCIS often develops into invasive breast cancer, it is almost always treated with surgery to remove all of the DCIS tissue.
The study appears in the Aug. 11 issue of the journal TheLancet.
In the U.S., magnetic resonance imaging (MRI) is currently recommended in addition to an annual mammogram only for very high-risk women. But researcher Christiane K. Kuhl, MD, of the University of Bonn, says the new findings could mean a much broader use for breast MRI screening in the future.
"I would go so far as saying this is the beginning of the death of mammography, but it is going to be a very, very slow death," Kuhl tells WebMD.
"It will take many years before we have enough randomized prospective trials to fully confirm our findings and enough radiologists who are qualified to perform MRI to screen for breast cancer."
The Problems With MRI
Debbie Saslow, PhD, of the American Cancer Society, is unconvinced. She tells WebMD that mammography is, and will remain, the screening tool of choice for breast cancer for at least the next decade.
"We will see more technologies like MRI approved for use along with mammography," she says. "But I don't know anyone who believes that any of these technologies are candidates for replacing mammography."
Availability and cost are presently two important obstacles to a broader use of breast MRI in the U.S., but they are not the only ones, Saslow says.
A breast MRI can cost $1,000 to $1,500 -- ten times the typical cost of mammography. And there are currently not enough radiologists trained in the procedure or dedicated breast MRI machines to provide screening to a larger population of women.
But false positive results remain the biggest impediment to the use of breast MRI in the screening of average-risk women, Saslow says.
In the roughly 2% of American women who are considered to be at high risk for breast cancer, the benefits of screening MRI outweigh these risks, but Saslow says this is not true for most other women.
"For average-risk women, the harms of MRI outweigh the risks," she says. "In addition, there have been no studies, including the current one, which assessed MRI screening of women who were not at high risk."
Roughly one in six (29 of 167) of detected DCIS cases in the study by Kuhl and colleagues occurred among average-risk women. The rest, Saslow points out, occurred in women with a known elevated breast cancer risk.
Ninety-three were referred for MRI because of abnormal mammograms, 18 had been treated for breast cancer, and eight had family history of the disease.
"The women in the study were not representative of the population at large, so it doesn't tell us much about the use of MRI in average-risk women," she says.
The Promise of MRI
About 20% of breast cancers now detected are confined to the milk ducts, compared to just 2% prior to the widespread use of mammography.
In an editorial accompanying the German study, radiology professor Carla Boetes, MD, PhD, of Radboud University in The Netherlands, writes that while mammography had dramatically improved the detection of these very early breast cancers, wider use of screening MRI might have an even greater impact.
"That only 20% of tumors detected through screening are pure DCIS is disappointing, when one keeps in mind that most breast tumors probably evolve from DCIS," she writes. "The observation that MRI detects many DCIS lesions that go unnoticed on mammography implies that some invasive carcinomas can be prevented by timely intervention on the basis of MRI findings."