Studies have suggested that MRI is better for breast cancer evaluation than conventional mammography and sonography and even have reported that the technique accurately detects breast cancer almost every time. However, many studies have reported that it misses both invasive and noninvasive breast cancer about 4 to 12 percent of the time. Additionally, it costs more to perform than the conventional methods and is less available in clinical settings. Therefore, MRI should never completely replace mammography or sonography, stated Dr. Susan Orel of the University of Pennsylvania in Philadelphia in a review.

Orel notes that the available evidence indicates that MRI is the most accurate method for monitoring the effectiveness of chemotherapy, especially in cases in which the patients do not respond or only partially respond to treatment. However, the image contrast decreases for patients who respond the best to chemotherapy, which can lead to an overestimation of the treatment effectiveness. MRI also can reveal the stage of breast cancer better than other methods, but it can enhance the contrast of benign lesions as well.

Most importantly, MRI can detect both invasive and noninvasive breast cancer not found by conventional means. For example, it has been shown to perform better than mammography when cancer occurs simultaneously in both breasts.

For patients belonging to certain high-risk populations, annual MRI screening has proved a useful addition to mammograms and sonograms. However, Orel states that further study is needed to assess whether other patients with negative mammograms and sonograms also should undergo MRI, especially because of the cost and lack of availability. (Journal of Clinical Oncology, Feb. 10, 2008, pp. 703-711.)