Project Abstract: Patient-derived model systems are commonly used to study tumor biology and test novel treatments for head and neck cancer. These models are established using patient tumors sourced from surgical specimens and typically implanted into the subcutaneous tissue of the mouse. There is little data available to support the decisions we make during the initial handling of the tumor samples and, most importantly, how these decisions impact the results of subsequent studies. Our long-term goal is to improve outcomes for head and neck cancer patients using valid, predictive, and well characterized model systems. The overall objective of this application is to improve our use of these mammalian model systems by understanding the impact of choices we make when we establish them. By combining innovative approaches to study cancer evolution with rigorous assessment of tumor biology and therapy response we hope to ultimately improve the relevance of studies using these mammalian models to improve the care of human patients. Our central hypothesis is that the approach used to establish patient-derived xenografts has a critical impact on their relevance as translational models. To achieve our goals, we proposed three aims. In Aim 1, we will determine the role of heterotopic vs. orthotopic implantation on the biology of the tumor, how patient-derived animal models change with increasing passage in animals, and how these factors impact tumor evolution. In Aim 2, we will test the concordance of response between patient derived models and patients by using patient derived xenografts established as part of an ongoing (and separately funded) window-of-opportunity trial and will assess consistency in response to standard treatments over time. In Aim 3, we will use an innovative humanized mouse model developed at Wisconsin to assess the evolutionary interplay between the tumor and immune system, understand whether these novel mice replicate the tumor/immune interface seen in human cancers or in syngeneic HNC models, and investigate how well the response to immunotherapy replicates that seen in patients. In summary, these studies will provide compelling evidence for how to optimize our use of mouse models of human head and neck cancer. Completion of this project will provide robust evidence delineating and refining best practices for the translational use of patient derived xenograft animal models of head and neck cancer.