Because the electrical properties of many breast tumors are different from those of surrounding, normal tissue, imaging these properties may provide useful diagnostic information. At the present time, X-ray mammography is the standard imaging modality used for breast cancer screening. The interpretation of EIT imaging is thus enhanced by its use together with x-ray mammography in the same geometry. This paper reports the ability of Electrical Impedance Spectroscopy (EIS) to localize and distinguish cancers from normal tissues. These findings are confirmed by simultaneous, co-registered 3-D mammograms or tomosynthesis images and are verified with biopsy reports.