 Positron Emission Tomography Imaging with 3-Deoxy-3-18FFluorothymidine FLT can selectively identify proliferating and non-proliferating tissues, including tumors. FLT uptake in the tumor is an indirect marker of DNA synthesis activity, which is a target of chemotherapy. Our hypothesis is that early change in FLT uptake in tumor with chemotherapy will predict pathological response to neoadjuvant therapy in breast cancer. Tumor uptake of FLT will be imaged and measured with positron emission mammography PEM, a PET scanner optimized for breast imaging with a significantly improved resolution compared to conventional whole-body PET imaging systems. 