Women diagnosed with early-stage breast cancer are faced with a tough choice either to have parts of the affected breast removed, a procedure followed by several weeks of potentially toxic radiation therapy, or to opt for a mastectomy, removing the entire breast and contending with the disfigurement that entails. The decision typically rests on where and how widespread the tumors are. It's no wonder, then, that more and more women are relying on high-tech MRI (magnetic resonance imaging) scans to help them examine their cancer and choose the right treatment.
But that may not be such a good idea, say researchers in a commentary appearing in CA: A Cancer Journal for Clinicians, a publication of the American Cancer Society. The authors looked at studies pitting preoperative use of MRI, which relies on magnetic waves, against mammograms and similar tests that use radiation to take pictures of breast tissue. Researchers found that women choosing MRIs often ended up with more aggressive surgery much of which wasn't necessary than women who did not use the scans. What's more, employing the newer and more sensitive MRI technology did not improve a woman's chance of surviving cancer or her chances of avoiding a recurrence of tumors.
While there is no doubt that MRIs are more sensitive than mammograms, says Dr. Daniel Hayes, clinical director of breast oncology at the University of Michigan Comprehensive Cancer Center and a co-author of the commentary, it's not clear that the technique is more specific than mammography. Studies of each diagnostic screen have shown that compared to mammograms, MRIs can pick up additional cancer lesions 16% of the time. "But," says Hayes, "the question is whether they are biologically important."
The risk of recurrence in women treated for early-stage breast cancer ranges from 5% to 10% in the 10 years after diagnosis. Three decades of studies have shown that lumpectomy combined with radiation therapy yields the same survival and recurrence rates as mastectomy; while more cancer may remain in a breast following lumpectomy, these lesions are generally destroyed by the radiation, which gives the two procedures the same outcomes. Yet women receiving an MRI tend to choose the more invasive approach.
Why? Because MRI is particularly good at diagnosing small tumors and picking up abnormalities that mammograms may miss in young women with dense breast tissue which may cause undue anxiety. Evidence suggests that women who opt for MRIs tend to react to seeing their lesions, whether they are cancerous or not, by having their entire breast removed rather than just a portion of the tissue. "I just saw two patients who both had MRIs done at an outside institution, and both came in wanting mastectomies based on the MRI findings," says Dr. Anthony Lucci, a surgical oncologist at M.D. Anderson Cancer Center in Houston. Neither of the MRIs showed cancer, just abnormalities, says Lucci, but more and more patients are requesting an MRI not as a diagnostic screening tool but as a prognostic one. And in those situations, "they are much more likely to request a mastectomy if the MRI reveals an abnormality," he says.
According to the studies that Hayes and his co-author, Dr. Nehmat Houssami, analyzed, such mastectomies are often unnecessary; earlier studies have shown that many of the small cancers that a lumpectomy may leave behind are in the same region as the surgery site, and therefore will most likely be destroyed by the radiation treatment that follows. "Radiation is very good," says Dr. Larry Norton, a breast-cancer specialist at Memorial Sloan Kettering Cancer Center in New York City. "We do know that if you don't irradiate a breast after surgery, you get local recurrence."
Aside from increasing the rate of radical surgery, the use of MRIs may also harm patients who already have a diagnosis. Patients may take several weeks to investigate the lesions, get biopsies and wait for pathology results, delaying the actual treatment of cancer.
So why do women continue to insist on having an MRI? Part of it has to do with the culture of technology: we believe that newer and more is better. Part of it also can be traced to a me-too spillover from the diagnostic arena. As a diagnostic tool, MRIs can be useful in picking up what mammograms may not find which is why the American Cancer Society, for example, recommends both screens for otherwise healthy women with a strong family history of the disease and younger women with dense breast tissue.
Hayes acknowledges that MRIs may also prove useful in detecting the spread of cancer from one breast to the other, but even here, he says, the data are still preliminary; MRIs may pick up about 3% to 5% of tumors that mammograms miss, but there is little evidence suggesting whether those additional tumors are malignant or benign. To find out the true benefit of MRI, he says, more research needs to be conducted. "Without randomized trials, we really don't know everything," says Norton.