The purpose of this research is to conduct a clinical study to evaluate the efficacy of a noninvasive and quantitative tool for classification/diagnosis of breast masses. The general goal of this project is to apply a technique called Sub-Hertz Analysis of Visco-Elasticity (SAVE), to increase specificity in the characterization of breast masses. This technique is based on measurement of the strain retardance-time parameter, which characterizes slow deformation of tissue due to a constant force. This parameter is representative of tissue viscosity and elasticity. The novelty of this proposal lies in the fact tht, in contrast to other existing elasticity imaging methods, the SAVE technique explores tissue dynamic response in the frequency range below 1 Hz. To our knowledge, our sub-Hertz method is the only elasticity imaging approach that explores this range of frequency spectrum, and the proposed research will be the first study in which this technique will be tested on a large group of patients. Our preliminary results have shown that SAVE provides reliable discrimination of benign lesions (fibrocystic change, fibroadenoma) from focal malignancies (infiltrating ductal and lobular cancers) with a remarkable specificity of 100% in a relatively small group of patients with non-palpable masses. Our general hypothesis is that by using SAVE, we will be able to improve pre-biopsy breast lesion classification in select groups of patients. This project includes the following Specific Aims: (1) Determine the specificity of SAVE by correlating its results with pathology in a population of patients with suspicious breast masses (BIRADS 4 or 5 lesions); (2) Determine the efficacy of SAVE in classifying non-specific masses in a group of breast patients on the follow- up list (BIRADS 3 lesions). Specific Aim 1 is designed to examine the efficacy of the SAVE method in patients with BIRADS 4 and 5 category lesions. In this Aim, the results of SAVE will be correlated to the biopsy results to evaluate the specificity of the proposed method in the high-risk group. Specific Aim 2 examines the patient population with probable benign breast masses, categorized as BIRADS 3 with recommendations for short-term follow up at 6-months intervals. This category is particularly challenging for both the clinician and the patient due to potentially prolonged diagnosis, stressful wait time, and the associated cost. In this aim, the results of SAVE will be correlated with the clinical results, which may include biopsy, at thei re-evaluation visit(s). Successful completion of this research will open the way for a new clinical tool that may be used for classification of breast masses. The proposed method is noninvasive, low cost, easy to use, and compatible with current ultrasound technology, which means that this technology can be readily translated to the clinic and become available to a wide range of breast patients. Consequently, this research has the potential to provide significant impact in breast cancer diagnosis and in reducing unnecessary biopsies.