Breast cancer best seen by MRI

Magnetic resonance imaging (MRI) is more accurate than mammography, ultrasound or clinical examination in detecting breast cancer in women with a hereditary risk for the disease, a study has found.

The findings, reported in this week's issue of the Journal of the American Medical Association, affect women who carry the so-called BRCA1 or BRCA2 gene mutations. Those mutations are responsible for 2 percent of all breast cancer cases, although many more women have a family history of breast cancer, a study author said Tuesday.

Without preventive surgery, women with BRCA gene mutations have a lifetime risk of breast cancer as high as 85 percent.

That is significantly higher than the lifetime risk for the general population, which is one in eight, said Dr. Ellen Warner, a medical oncologist at the Toronto Sunnybrook Regional Cancer Centre, who led the investigation.

"Our results support the position that MRI-based screening is likely to become the cornerstone of breast cancer surveillance for BRCA1 and BRCA2 mutation carriers," the authors wrote.

Dr. Warner stressed that MRI "is not for the general population."

MRI, widely used since the 1970s, makes use of the magnetic properties of cell nuclei to create images of living cells. With this technology, images are developed from data generated by protons inside the nuclei of hydrogen atoms. These protons emit signals that computers can convert to pictures when placed in a strong magnetic field and pummeled with radio waves.

Current recommendations by the National Comprehensive Cancer Network (NCCN), an alliance of 19 of the world's leading cancer centers, say women with BRCA gene mutations should, beginning at age 25, undergo mammograms yearly and clinical breast examinations every six months.

But authors of the report in JAMA point out that many tumors in this at-risk population are detected at a relatively advanced stage, when treatment is more difficult.

Dr. Warner said an analysis by New York researchers found that half of breast cancer cases in a study group were missed by a combination of mammograms and clinical breast examinations. "The cancers in a lot of those women spread, and they died. You want to get the tumor before you can feel it," she said.

It previously had been recognized that adding MRI and ultrasound to the diagnostic protocol might improve the ability to detect breast cancer at an earlier stage.

The Toronto study, which involved 236 women ages 25 to 65, all of whom had the BRCA mutations, determined MRI was the most effective diagnostic tool.

In the study, the women who participated each underwent one to three annual screening examinations, consisting of MRI, mammograms and ultrasound, at a teaching hospital between November 1997 and March 2003. Ultrasound is another type of computerized imaging, which records data from sound waves.

On the day of imaging and at six-month intervals, the subjects also underwent clinical breast examinations.

During the study period, 22 breast cancers were detected, some by multiple examination methods. Seventeen of the cancers (77 percent) were found by MRI; eight (36 percent) were detected by mammograms; seven (33 percent) were found by ultrasound; and two (9.1 percent) were discovered by clinical breast examinations.

The investigators determined that all four screening methods combined had a sensitivity rate of 95 percent. That compared with a rate of 45 percent for mammography and clinical breast examinations combined.

The American Cancer Society says about 270,000 U.S. women were diagnosed with breast cancer in 2003, and nearly 40,000 died from the disease.