NEW YORK (Reuters Health) - For women diagnosed with breast cancer in one breast, MRI is useful in detecting cancer in the opposite breast that may have been missed with mammography and clinical examination, new research shows.

Up to 10% of women who have received treatment for unilateral breast cancer have involvement of the other breast as well, according to the report in The New England Journal of Medicine for March 29. The focus of the present study was to determine if MRI evaluation can improve the detection of contralateral malignancies.

The study involved an MRI assessment of 969 women who were recently diagnosed with unilateral breast cancer and had no apparent disease in the opposite breast, according to mammography and clinical examination. MRI-detected breast cancer was confirmed with biopsy and the absence of disease on MRI was confirmed with biopsy, repeat imaging or both.

MRI detected cancer in the contralateral breast of 3.1% of the women, lead author Dr. Constance D. Lehman, from the University of Washington Medical Center in Seattle, and colleagues note. The sensitivity, specificity, and negative predictive value of MRI in detecting cancer in the contralateral breast were 91%, 88%, and 99%, respectively.

A positive MRI finding led to biopsy in 121 women (12.5%). Thirty of the specimens contained cancer, including 18 with invasive disease. The average diameter of the invasive tumors was 10.9 mm.

Breast density, menopausal status, or the histologic features of the primary tumor had no bearing on the additional number of cancers detected.

In a related editorial, Dr. Robert A. Smith, from the American Cancer Society in Atlanta, comments that it may be argued that the added sensitivity of MRI of the contralateral breast comes at high cost in terms of false-positive results and overdiagnosis. Nevertheless, the false positive rate and the predictive value of a positive test fall within an acceptable range, and there is little persuasive evidence that most cases of ductal carcinoma in situ are not progressive."

"Therefore," Dr. Smith concludes, "there is value in detecting and treating malignant tumors in the contralateral breast that were not identified by means of mammography and clinical breast examination."