The ability of the surgeon to accurately visualize tumor margins and identify metastases is necessary for the success of any cancer operation. Fluorescence imaging, because of its high sensitivity, low cost, portability, and real-time capabilities has great potential to improve surgical outcomes. Our laboratories have pioneered the use of fluorophore-conjugated tumor-specific antibodies for detection and resection of GI cancers in orthotopic mouse models with highly improved outcomes. Thus far, the fluorophores that we have utilized have been in the visible range of light. There are numerous advantages to near infrared (NIR) fluorophores which have better tissue depth of penetration compared to fluorophores in the visible range. Furthermore, we now have humanized tumor-specific anti-CEA and anti-CA 19-9 antibodies that can be used for future clinical trials. The present grant application proposes to develop the potential of using humanized anti-CEA and anti-CA 19-9 antibodies conjugated with appropriate fluorophores in the NIR 700 to 800 nm range to label primary tumors and their metastases for fluorescence laparoscopic staging, fluorescence-guided surgery (FGS), and adjuvant photoimmunotherapy of pancreatic and colon cancer in patient-derived orthotopic xenograft (PDOX) models. The specific aims of this grant are: 1) Validation of NIR fluorophore-labeled tumor-specific humanized anti-CEA and anti-CA 19-9 antibodies to label primary tumors and metastases in PDOX mouse models of pancreatic and colorectal cancer, 2) Comparison of near infrared fluorophores conjugated to humanized anti-CEA and anti-CA 19-9 antibodies with different properties for dosing response, signal duration, photobleaching, signal-to- background ratio, and phototoxicity, in PDOX models of human pancreatic and colon cancer, 3) Development of intraoperative photoimmunotherapy (PIT) using the humanized anti-CEA and anti-CA 19-9 antibodies, or other antibodies shown to be effective in Aims 1 and 2, conjugated to IRDye 700DX as adjuvant treatment to FGS for pancreatic and colorectal cancer in PDOX nude and NSG-humanized mouse models. The completion of these aims will set the stage for clinical trials of fluorescent-antibody-based FGS that can change the paradigm of surgical oncology and greatly improve outcomes of recalcitrant cancers. Grant application features: Humanized tumor specific monoclonal antibodies Very bright tissue penetration near infrared dyes PDOX mouse models targeting recalcitrant pancreatic and colorectal cancer Fluorescence guided surgery Adjuvant photoimmunotherapy