MR jockeys with x-ray mammo as screening modality

Ask anyone in women's health about screening for breast cancer and the response will very likely involve x-ray mammography. Some, particularly the vendors of this equipment, will acknowledge the potential contributions of other methods, such as breast MR, but these typically will be framed as complementary to the traditional screening tool.

Findings published in the August issue of Radiology however, could change such conversations.

A multicenter study found that screening MR allows detection of more breast cancers in high-risk women, accurately identifying tumors missed by mammography and ultrasound.

"Women at high risk for breast cancer can benefit from undergoing screening MR," said Dr. Constance Dobbins Lehman, lead author of the Radiology paper and director of breast imaging at the Seattle Cancer Care Alliance. "Of all the breast imaging tools we have currently available, MR is clearly the best at detecting cancer."

In research at six facilities, the multicenter team compared three screening methods in women at high risk for breast cancer: MR, mammography, and ultrasound. Each of 171 asymptomatic women over age 25 (average age 46), with at least a 20% lifetime risk of developing breast cancer, underwent exams with all three modalities.

Initial findings led to 16 biopsies. These found six cancers, an overall cancer yield of 3.5%. All six of the cancers were detected with MR. Only two were detected with mammography and one with ultrasound. The four cancers found in women with dense breast tissue were detected only with MR.

Biopsy rates were 8.2% for MR and 2.3% for mammography and ultrasound. The positive predictive value of biopsies performed as a result of MR findings was 43%.

Compared with mammography and ultrasound, screening with MR will allow detection of 23 more cancers per 1000 high-risk women screened, concluded the researchers, who endorsed the use of MR as a screening tool for women genetically predisposed to breast cancer but not the general population.

"Although MR is a very powerful tool for detecting cancer, it is not perfect," said Lehman, a professor of radiology at the University of Washington. "There are benign areas of breast tissue that can look suspicious but do not represent breast cancer and yet may lead to a biopsy."

While MR has been shown effective as a screening tool for women genetically predisposed to developing breast cancer, there is no evidence to support MR screening in average-risk women.

According to the National Cancer Institute, genetic predisposition accounts for 5% to 10% of all breast cancers. Women who are genetically at high risk for breast cancer need to begin screening at a younger age, because they often develop cancer earlier than women at average risk. Women below age 50, however, are more likely to have dense breast tissue, which can limit the effectiveness of mammography as a screening tool. The American Cancer Society recommends that women with a high risk of developing breast cancer should be screened with MR, in addition to their yearly mammogram, beginning at age 30.

"It is frightening to be told that you're at very high risk for developing breast cancer," Lehman said. "It's important that these women understand that there is something they can do to increase their chances of early detection in the event that they do develop breast cancer."