Applying a constant voltage with multiple sinusoidal frequencies in the range of 10 Hz to 500 KHz between a distal reference electrode and a scan probe placed on a region of interest, exit currents from an array of electrodes inside the probe kept at the ground potential are measured to form multi-frequency trans-admittance maps. Observing that frequency-difference trans-admittance maps reflect a complex conductivity distribution underneath the probe, we analyzed the relationship between the map and the complex conductivity and suggested a new anomaly detection algorithm providing its location and size. We describe experimental results of the new technique for possible clinical applications of breast cancer diagnosis. We found that an anomaly as small as 4mm diameter at the largest depth of 15mm can be detected from frequency-difference trans-admittance maps with one frequency below 500 Hz and the other greater than 50 KHz. The anomaly location including its transversal position in the probe plane and depth can be estimated directly from the multi-frequency trans-admittance map. However, estimation of the anomaly size needs a calibration to remove uncertainty of unknown scale factor. We suggest future works of more experimental studies using realistic breast phantoms and human subjects.