MRI is more accurate than mammogram in high risk patients

Question Is magnetic resonance imaging more accurate than mammography in women at high risk of breast cancer?

Synopsis Magnetic resonance imaging (MRI) is an expensive test, but it may be more sensitive than mammography. The authors identified 1909 Dutch women aged 25-70 years with at least a 15% lifetime risk of breast cancer. This group included 358 carriers of mutations (largely BRCA1 and BRCA2) cancer, 1052 women with a 30% to 49% risk, and 499 with a 15% to 29% risk. Of these, 4.6% were lost to follow up, largely because they underwent prophylactic mastectomy. Another 4.7% refused MRI, usually because of claustrophobia. The mean age was 40 years; only 15% had never had breast cancer screening, and about 75% were premenopausal. Women underwent a clinical breast examination every six months, as well as annual MRI and mammography, which were interpreted independently by radiologists blinded to results from the other method. The women were followed up for a median of 2.9 years. A breast imaging reporting and data system (BI-RADS) classification of 0 (“need additional imaging”), 3, 4 or 5 was considered a positive screening test result (a classification of 1 or 2 indicates normal or nearly normal). The reference standard was histological examination, and sensitivity and specificity were calculated by comparing the number of cancers detected by each method, plus any interval cancers. In addition to sensitivity and specificity, the ability to detect earlier cancers was evaluated by comparison with an unscreened control group who had a similar risk of breast cancer. MRI was more than twice as sensitive as mammography regardless of the cut off used to define an abnormal test result (79% v 33%), although it was somewhat less specific (89.8% for BI-RADS of 0, 3, 4, or 5 as abnormal compared with 95% for mammography). The area under the receiver operating characteristic curve, a measure of overall diagnostic accuracy, was significantly greater for MRI (0.83 v 0.69). However, the lower specificity means that women underwent more unnecessary additional follow-up exams (420 v 207) and had more unnecessary biopsies (24 v 7) because of the addition of MRI screening. The comparison with unscreened control groups, although imperfect, found that fewer women screened with both MRI and mammography were node positive.

Bottom line Magnetic resonance imaging is better at ruling out breast cancer (that is, more sensitive) than mammography, but is also more likely to produce false positive results (less specific). It is also more expensive and leads to more unnecessary biopsies and follow up studies. This makes it inappropriate for women at average or low risk, but it may be a good option for high risk women who understand these limitations.

Level of evidence 2b (see www.infopoems.com/levels.html). Any of: independent blind or objective comparison; study performed in a set of non-consecutive patients, or confined to a narrow spectrum of study individuals (or both), all of whom have undergone both the diagnostic test and the reference standard; a diagnostic clinical rule not validated in a test set.