Squamous Cell Cancer

The goal of this study is determine the safety and tolerability of orally taken probiotic (R-5780) in patients currently on a PD-1 Pathway Checkpoint Inhibitor (checkpoint protein on immune cells called T cells) with Solid Tumors.

The goal of this Phase 1 clinical trial is to evaluate the safety and feasibility of nivolumab-IRDye800CW (nivo800) as a molecular imaging agent in adults with biopsy-confirmed or presumed head and neck squamous cell carcinoma (HNSCC) who are scheduled to undergo standard-of-care surgical resection. The main questions it aims to answer are: * Is nivolumab-IRDye800CW (nivo800) safe when administered before surgery, as measured by the occurrence of clinically significant Grade ≥2 adverse events that are possibly, probably, or definitely related to the study drug? * What is the extent of pathological response at each dose level, including residual viable tumor, fibrosis, necrosis, and tumor-infiltrating lymphocyte characteristics? Participants will: * Receive two intravenous infusions during the preoperative period, approximately 2-3 weeks before surgery and again 1-2 days before surgery. * Undergo standard-of-care surgical resection with collection of tumor and lymph node specimens for pathological and imaging studies.