MRI excels at detecting breast cancer, research finds

Canadian study focused on women with genetic predisposition to tumors

September 15, 2004|By David Kohn | David Kohn,SUN STAFF

For years, mammography and manual breast exams have been primary tools for spotting breast cancer. But both tests are frustratingly imprecise and miss many cancers until the tumors have spread. Now another technique might offer better results for women at high risk.

Magnetic resonance imaging is far more accurate, according to a study by Canadian researchers. The findings could lead to a sharp increase in the use of MRI, especially among high-risk women.

"The MRI is very sensitive," said Dr. Steven Narod, an epidemiologist at the University of Toronto and an author of the study, which appears in today's issue of the Journal of the American Medical Association. "With mammography, there's always the possibility that you've missed the cancer."

The scientists looked at 236 Canadian women ages 25 to 65, all of whom had genetic mutations known as BRCA1 or BRCA2. Over their lifetimes, women with these mutations have up to an 85 percent chance of developing breast cancer, a much higher risk than the general population.

From 1997 to 2003, each of the women was screened annually using four different methods: MRI, mammography, and ultrasound and manual exams.

Over that time, 22 cancers were found. The MRI detected more than three-quarters of these, while mammography and ultrasound detected only a third. Breast exams spotted less than 10 percent.

MRIs also tended to catch the tumors when they were smaller, before they had spread widely.

Researchers said the results could increase use of breast cancer MRI screening. "I think [MRI] is going to be accepted pretty quickly," Narod said. "Within a year it's going to be part of clinical practice."

Over the past few years, several studies have examined MRI screening for breast cancer. Most reported encouraging results, including a study published in July by the New England Journal of Medicine. But this latest study was the first to compare it to mammography, ultrasound and manual exams - and the first to focus solely on women with the BRCA mutation.

MRI uses magnetic energy to produce a three-dimensional picture of living tissue. Mammography, using low-level radiation, creates a two-dimensional image. Ultrasound uses sound waves to construct an image somewhere between two and three dimensions.

About 200,000 Americans develop breast cancer annually, and 2 to 3 percent of them have the BRCA mutations. Women with the mutation are much more likely than others to develop cancer before they are 40.

Because their risk of developing cancer is so high, between a quarter and a third of women with the BRCA mutations choose to have their breasts removed as a preventative measure. This reduces the risk of breast cancer by 90 percent. But the use of MRI could offer such women a less drastic option.

"It gives them an alternative that allows them to preserve their breasts," said Mark Robson, clinical director of the Clinical Genetics Service at Memorial Sloan-Kettering Cancer Center in New York.

Robson, who wrote an accompanying editorial to the MRI research, praised that study for its rigor.

The study was limited to women with the BRCA mutation, so it's not clear whether MRI is a better diagnostic tool for women who don't carry it.

Some researchers suspect that the benefits of MRI would extend to other women with relatively high risk. A study published two months ago looked at a range of high-risk women - both BRCA carriers and women with a family history of breast cancer - and found MRI superior to other detection methods.

But most experts agreed that MRIs are not for everyone. "For women at normal risk, there's no evidence that supports the use of MRI as a screening test," Liberman said.

At $1,000 or more, an MRI costs about 10 times as much as a standard mammogram and, like a mammogram, it must be repeated annually. For women in the normal risk group, health insurance does not generally cover the test.

MRI "is an extremely expensive procedure," said the study's lead author, Ellen Warner, a medical oncologist at the Toronto-Sunnybrook Regional Cancer Centre.

Warner noted that MRIs also increase other costs - a positive MRI is usually followed by more MRIs or a breast biopsy, which is even more expensive. And because MRIs are so sensitive, they tend to produce a high rate of false positives.

Doctors and patients will now have to decide these issues, Narod said: "It would be very hard to tell my patients, `Mammography doesn't really work, but it's cheaper, so let's use that.' MRI will find the cancer before mammography almost every time."

Another key question is whether finding tumors earlier saves more lives. Warner and others caution that the jury is still out on that issue: They suspect that some types of breast cancer might be deadly no matter when treatment begins.

But most experts suspect that improved detection will increase survival rates. The Toronto researchers are beginning a follow-up study to see whether women whose cancers were spotted by MRI survive longer.

"We feel fairly confident that [MRI] will improve mortality," said another author, Donald Plewes, an imaging physicist at Sunnybrook and Women's College Health Sciences Centre. "But we have to prove it."

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