We developed a tri-modality imaging system for breast cancer imagingby integrating photoacoustic (PA) and thermoacoustic (TA) imaging techniques into a modified commercial ultrasound scanner. Laser and microwave excitation pulses were interleaved to enable PA and TA dataacquisition in parallel at the rate of 10 frames per second. The performance of the tri-modality imaging system was evaluated in-vitrousing phantom samples. A plastic tube (7 mm inner diameter, 25 mm length) filled with 30 mM methylene blue dye placed at a depth of 8.4cm in chicken breast tissue was successfully detected in PA images with an ultrasonic bandwidth of 15 MHz. The SNR at this depth was 15dB after averaging 200 signal acquisitions. Similarly, a plastic tube (7 mm inner diameter, 25 mm length) filled with high concentration salt water placed at a depth of 5.1 cm in porcine fat tissue was successfully detected in TA images. A PA noise-equivalent-sensitivityto methylene blue solution of 260 nM was achieved in chicken tissueat a depth of 3.4 cm and with a laser fluence of 17 mJ/cm2.