Despite clinical assessment and mammography, as many as 10% of women treated for breast cancer have unrecognized disease in the other breast. Preliminary studies suggest that magnetic resonance imaging (MRI) is able to detect many otherwise occult contralateral tumors. This study attempted to show whether MRI does in fact aid the detection of contralateral breast cancer. A total of 969 women aged 18 and older who recently were found to have unilateral breast cancer participated in the study. In all cases the other breast was normal clinically and on mammography. MRI-detected cancers were confirmed by biopsy within a year of entry into the study. Contrast-enhanced MRI was performed using a dedicated breast-surface coil. Participating radiologists were experienced in interpreting breast MRI scans.
The primary breast cancer was infiltrating ductal carcinoma in 58% of women taking part in the trial and ductal carcinoma in situ in another 20%. Thirty-three contralateral breast tumors were found within a year after the trial began. Thirty of them were diagnosed by MRI after a normal clinical breast examination and negative mammogram, for a diagnostic yield of 3.1% (95% confidence interval [CI], 2.0–4.2). Breast MRI was 91% sensitive and 88% specific in detecting contralateral breast cancer. Its positive and negative predictive values were, respectively, 21% and 99%. A biopsy was recommended for 135 women, 121 of whom underwent the procedure. The rate of positive biopsy findings was 25%. Eighteen of the 30 cancers found by MRI were invasive; their mean diameter was 10.9 mm. The number of additional cancers detected by MRI was not influenced by breast density, menopausal status, or whether the primary tumor was an invasive or in situ, or a lobular or nonlobular, tumor. The specificity of MRI was higher for postmenopausal than for pre- or perimenopausal women, and the same was the case for the positive predictive value of the study and the rate of positive biopsies. All but one of the cancers were stage 0 or stage 1 lesions.
These findings demonstrate that MRI can detect contralateral breast cancers that are missed by clinical examination and mammography at the time a primary cancer is diagnosed. While the study is presently too costly to recommend for widespread use in the general population, it does aid the detection of contralateral disease in women at increased risk such as those with recently diagnosed unilateral breast cancer.