Two-dimensional optoacoustic imaging with a hand-held probe operated in backward mode is being developed for diagnostic imaging of breast cancer to evaluate the feasibility of a dual-modality optoacoustic plus ultrasonic system that maps functional information of anatomical tissue structures with ultrasonic resolution. Tissue is illuminated at 757nm and 1064nm for optical contrast between hypoxic blood of breast carcinomas and normally oxygenated blood in benign masses. The system is optimized and calibrated in phantoms for a pilot clinical study of patients with breast masses suspected for malignancy. Capability of the non-invasive system to improve detection and diagnosis of breast tumors is discussed.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.