MRI scans beat mammograms for finding tumors in women at high risk of breast cancer, but at a far greater cost and chance of unneeded biopsies, new research suggests.
Those drawbacks make MRIs unsuitable for screening average-risk women, who are still advised to get regular mammograms starting at age 50.
But the benefit of better detection from MRI, or magnetic resonance imaging, makes it worthwhile for women with faulty genes or a strong family history of breast cancer, like a mother or sister who had the disease.
``Women who are at high risk should consider getting MRI besides mammography,'' said Dr. Stephen Feig, a radiology professor at Mount Sinai School of Medicine in New York and past president of the Society of Breast Imaging.
He had no role in the new research, which was done by doctors at six cancer centers throughout the Netherlands and was partly funded by the Dutch Health Insurance Council. Results were reported in Thursday's New England Journal of Medicine.
In the study, MRIs caught nearly twice as many tumors as mammograms did in women at high risk of breast cancer. For them, the value of screening is not as much of an issue as it has been in recent years for women at average risk.
Researchers studied 1,909 Dutch women including 358 with one of the BRCA genes or other mutations that predispose women to breast cancer. Up to half of such women get it by the time they're 50, and they are also prone to ovarian cancer.
They can cut their risk of cancer and death by having their breasts or ovaries removed, or by taking estrogen-blocking drugs. But many don't want such drastic measures, and researchers wanted to see if intensive screening could help such women by finding tumors early, when they're most treatable.
They compared mammograms, which are breast X-rays, to MRI scans, which use magnets to make detailed images without radiation. An MRI scan costs $700 to $1,000 _ about 10 times the cost of a mammogram. Some large insurers already cover MRIs for women at high risk.
Women were screened three ways: a breast exam by a doctor every six months, annual mammograms and annual MRI scans. Results were analyzed by different doctors, so none knew what the others had found.
After an average of nearly three years, 51 breast cancers had been identified. Some results were excluded for various reasons. Of the remaining 45 tumors, 32 were identified by MRI, including 22 that hadn't been visible on mammograms. Only 18 of the 45 tumors were caught by mammograms, a lower rate than studies typically show, some experts noted. In the United States, mammography is thought to miss 15 percent to 25 percent of cases.
Still, experts acknowledged that MRI was superior at detection. But the scans also gave more false alarms.
``MRI led to twice as many unneeded additional examinations as did mammography (420 vs. 207) and three times as many unneeded biopsies (24 vs. 7),'' the authors reported.
Both kinds of screening did find cancers early. Researchers compared women in the study with two other groups: breast cancer patients participating in a different study on faulty genes, and all women diagnosed with breast cancer in the Netherlands in 1998.
Tumors in the women in the screening study were smaller and less likely to have spread to lymph nodes. Many women in the study also had cancer detected at a young age.
``Our study firmly establishes the value of screening for women with inherited predisposition for breast cancer, provided that MRI is added to mammography,'' said the lead researcher, Dr. Jan G.M. Klijn of Erasmus Medical Center-Daniel den Hoed Cancer Center in Rotterdam.
But doctors are hesitant to recommend it in place of preventive surgery without proof it saves lives.
``The prognosis is better for small, early cancers, but detecting small cancers at an early stage does not guarantee improved survival rates,'' Dr. Laura Liberman of Memorial Sloan-Kettering Cancer Center in New York cautioned in an accompanying editorial.
Klijn was optimistic that proof would come.
``Although the follow-up is still very short, we expect a mortality reduction of at least 20 percent to 25 percent after 15 years of follow-up,'' he said.
The American Cancer Society recommends that women at high risk consider having an MRI plus mammography but not in place of it, because mammography found some cancers that MRI missed, said Dr. Robert Smith, the society's director of screening. Women must be counseled carefully about whether to try intensive screening instead of having their breasts or ovaries removed.
``No physician is going to be able to say with complete certainty that you can choose any one of these options and it will provide you with a better guarantee,'' he said, but added: ``It would be ideal to try to avoid the surgery if you could.''
If women do get an MRI, they should time it for midway through their menstrual cycles when results are best, and they should go to centers capable of performing MRI-guided biopsies if a scan shows something that needs follow-up, Liberman suggested.
Breast cancer is the most common cancer in American women after skin cancer. About 216,000 new cases will be diagnosed this year, and it will cause about 40,000 deaths.