Microwave-induced thermoacoustic tomography (TAT) is a noninvasive, nonionizing modality based on the inherent differences in microwave absorption of malignant breast tissues and normal adipose-dominated breast tissues. In this paper, a TAT system based on multielement acquisition system was built to receive signals. Slices from different layers in the sample were composed into a three-dimensional (3D) volume. Based on the 3D volume, inherent differences in microwave absorption between different biological tissues can be converted into structure information. Our experimental results of some mimicked and human tumors indicate that TAT may potentially be used to detect early-stage breast cancers with high contrast.