We propose to validate the potential role of our novel near-infrared (NIR) diffuse optical tomography guided by ultrasound (NIR/US) imaging system in assessing patient pathological response to neoadjuvant chemotherapy (NAC). NIR/US is implemented by simultaneously deploying NIR optical sensors and a commercial ultrasound transducer on a hand-held probe, and utilizing co-registered ultrasound to provide lesion structure information and guide optical tomography reconstruction. As a result, the optical tomography has overcome problems associated with intense light scattering and has provided reliable tumor hemoglobin distributions, which are directly related to tumor angiogenesis. Pilot data obtained from 32 patients who underwent NAC, which was assessed by NIR/US, have demonstrated that pretreatment tumor total hemoglobin (tHb) content predicts patient final pathological response with 79% sensitivity and 80% specificity. In addition, the percentage of total hemoglobin changes normalized to the pretreatment level (%tHb) can be used to further identify responders from non-responders at the end of cycle 1 (2-3 weeks) after the initiation of NAC. Furthermore, combining widely used tumor pathologic variables and receptor status with hemoglobin functional parameters obtained before the initiation of NAC can achieve 100% prediction sensitivity and specificity when baseline scatter data are included, or treatment regimens are categorized based on human epidermal growth factor receptor 2 (HER-2/neu) or the addition of %tHb at the end of treatment cycle 1 is assessed. In this proposal, we will: 1) Upgrade NIR imaging systems and validate NIR imaging algorithms optimized for imaging large lesions; 2) Validate the initial findings through the recruitment of approximately 80 patients who are undergoing NAC at the Hartford Hospital, the University of Connecticut Health Center, and the Waterbury Hospital; and 3) Perform data analysis a) to determine the best time-window to assess response based on cycle 1 %tHb for different treatment regimens; b) to validate the prediction model developed from pilot data based on tumor pathological variables (tumor type, grade and mitotic count), tumor molecular markers of estrogen receptor (ER), progesterone receptor (PR), and HER-2/neu, and pretreatment NIR functional parameters as well as scatter data and response rate based on one cycle of %tHb. The successful completion of the project will result in a powerful tool to manage personalized breast cancer treatment. In the genomic era of personalized medicine where predicting and monitoring of early responses for outcome prediction becomes crucial, our NIR/US technology will prove to be invaluable.