In women newly diagnosed with cancer in one breast, an MRI can find the disease in the opposite breast more effectively than standard mammography or clinical examination, scientists said Tuesday.
MRI, which stands for magnetic resonance imaging, detected cancers that had been missed by the other methods in 3.1% of patients in a large clinical study, researchers said.
The report, published online by the New England Journal of Medicine, means that nearly 180,000 women diagnosed with breast cancer in the U.S. each year should receive an MRI, said Dr. Constance D. Lehman, lead study author and professor of radiology at the University of Washington School of Medicine.
The additional screening could help spare women unnecessary mastectomies or repeated treatments because of the inaccuracies of conventional methods.
"What this has the potential to do is help women make better decisions about the course of their treatment," said Robert A. Smith, director of cancer screening for the American Cancer Society and author of an accompanying editorial.
Dr. John Glaspy, director of the outpatient oncology clinic at UCLA's Jonsson Cancer Center who was not involved in the research, said the study would change medical practice -- but at a cost of many millions of dollars. Each MRI costs $1,000 to $2,000, he said, about 10 times the expense of a mammogram.
"The tough issue it raises is that as technology gets better and the cost of healthcare rises higher, more people are going to be left behind and widen the disparity between the haves and have-nots," he said.
The study coincided with the release Tuesday of the American Cancer Society's new breast cancer screening guidelines, which for the first time recommend an annual MRI for high-risk women -- those with at least a 20% to 25% lifetime risk of developing the disease. Average lifetime risk for all women is 12% to 13%.
The high-risk group includes women who had received chest radiation between ages 10 and 30, had a genetic mutation making them susceptible to breast cancer, or had a relative with one of the key mutated genes.
The society said MRI screening was cost effective for the approximately 650,000 women in the high-risk group.
These women account for about 1% of the 65 million women older than 40 urged to get mammograms every year.
The society, however, did not recommend regular MRI screening for women who have had breast cancer, saying the risk of developing a second breast cancer was not high enough to justify the added screening cost.
Breast cancer is the second most common cancer in women, next to skin cancer.
The American Cancer Society estimates that 178,480 women will be diagnosed with the disease this year, and 40,460 will die of it.
Most patients have cancer in a single breast at the time of diagnosis, but about 10% will develop cancer in the opposite breast. When that happens, patients face a second round of treatment, which can include surgery, chemotherapy or radiation.
Mammography has long been the primary tool for detecting breast cancer in its earliest stages -- before tumors are large enough to detect in a clinical breast exam. Widespread use of mammography is largely responsible for the 24% drop in the breast cancer death rate from 1989 to 2003.
More recently, clinicians have debated the role of MRI. Although the technology is better at finding cancer than a mammogram, it is expensive and produces a relatively high number of false positive results that lead to unnecessary biopsies.
But the trade-offs make sense for newly diagnosed breast cancer patients anxious to know the extent of their disease, Smith said.
If an MRI found cancer in the opposite breast, a woman could treat the disease in each breast at the same time, he said.
On the other hand, a woman with a negative MRI could decide against a prophylactic mastectomy, which some women with cancer in one breast choose as a precautionary step.
The study, conducted at 25 U.S. test sites and paid for by the National Cancer Institute, looked at 969 women with recently diagnosed cancer in one breast but no cancer in the opposite breast based on a mammogram and clinical exam.
All women received an MRI of the opposite breast, which detected possible cancer in 121 women. A biopsy confirmed cancer in 30 women, or 3.1% of those in the trial. For the remaining 91 women, biopsies were negative.
Women in the study were followed for one year to see if cancer developed in the opposite breast that had not been detected by MRI.
Three women, or 0.3% of those in the study, had tumors in the opposite breast that had been undetected.
Researchers cautioned that MRI was not a substitute for mammography because MRI could not detect calcifications, one of the earliest signs of breast cancer.
Lehman said researchers were planning an economic analysis that would weigh the cost of MRI in all newly diagnosed women against the potential savings from second surgeries that were no longer needed.
Glaspy predicted that women would demand MRIs and that private insurers would cover them -- whether the tests saved money or not.
"This is a top-drawer journal, and the data is excellent," he said. "It's kind of a no-brainer."