Abstract Clinical need: Obtaining tumor-free margins is critical for local control in breast conserving surgery. Currently, 20-40% of lumpectomy patients have positive margins that require surgical re-excision which is a burden for patients, surgeons and the healthcare system. Therefore, it is of paramount importance that all cancer be resected from the tumor bed during lumpectomy surgery. Background: The LUM Imaging System consists of a fluorescence-based imaging agent, LUM015, a hand-held wide-field detector (LUM Imaging Device) used to image a tumor bed cavity in real-time, and a proprietary tumor detection algorithm that highlights regions of a tumor bed suspected to contain residual cancer. The LUM Imaging System may be used to scan the surgical cavity walls intraoperatively after the resection of the main lumpectomy specimen. Trial Objectives and Methodology: This multi-site study is designed to validate the process of implementing the LUM Imaging System into institution-specific workflows during lumpectomies and to correlate images generated by the LUM Imaging System with histopathology results. This study is a prospective, interventional feasibility study and is an introductory arm to a pivotal study which will evaluate the safety and efficacy of the LUM Imaging System in reducing the positive margin rate in excised tissue during standard of care lumpectomies. Up to 165 adult female breast cancer patients undergoing lumpectomies are being enrolled at up to eleven medical centers across the US. This study is being conducted under an Investigational Device Exemption granted by the FDA. This study evaluates the use of the LUM Imaging System within the scope of the study protocol, while maintaining institutional standards on maintaining specimen tissue orientation and nomenclature. Surgeons record images of in-vivo tissue and ex-vivo tissue to measure the ratio of fluorescent intensity between the in-vivo and ex-vivo images to verify that consistent tissue contact is made during lumpectomy cavity scanning. A comprehensive process to evaluate LUM System operation is implemented and will be reported. The novel imaging agent, LUM015, is injected into all enrolled subjects and safety data is being collected. Discussion: Successful implementation of standardized tissue collection, naming conventions, and LUM Imaging System training is intended to improve the quality and integrity of the data collected in the upcoming Pivotal clinical trial to evaluate the safety and efficacy of the LUM Imaging System. This System is also currently being evaluated in other cancer indications including gastrointestinal cancers, prostate cancer and brain cancer. This study is funded by a grant from the National Cancer Institute to support biomedical technology development. Citation Format: Jorge M. Ferrer, Shelly Hwang, Kelly Hunt, Daleela Dodge, Anees Chagpar, Stephen Grobmyer, Stephen Karp, Stephanie Valente, Irene Wapnir, Kate Smith, Elena Ramirez, Thomas Bischof, David Strasfeld, David Lee, Barbara Smith. Expansion into multiple institutions for training in the use of the LUM Imaging System for intraoperative detection of residual cancer in the tumor bed of female subjects with breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT166.