Purpose: This study will evaluate how measurements of tissue stiffness, viscosity, and anisotropy using non-invasive ultrasound imaging correlate with breast tumor malignancy and response to chemotherapy. Participants: Up to 200 women with benign or malignant breast tumors for arm 1 and up to 50 women undergoing neoadjuvant chemotherapy in the breast for arm 2 will be recruited. Procedures (methods): The research team will use an ultrasound scanner to acquire non-invasive elastography data from the breast of each subject, testing a range of transducer rotation angles. Transducer position will be monitored using a position sensor during imaging.