PROJECT SUMMARY/ABSTRACT Development of effective therapies is an urgent unmet medical need for patients with metastatic gastroesophageal adenocarcinoma (mGEA). The advent of immune checkpoint inhibitors such as anti- programmed death (PD)-1 antibodies has revolutionized treatment of some cancers but benefits only a minority of patients with GEA. Combination approaches are required to extend this benefit to more patients. Most studies of immunotherapy combinations in GEA initiate PD-1 blockade at the same time as cytotoxic therapy despite the possibility that cytotoxic agents may kill some of the very T cells invigorated by PD-1 blockade, as our group and others have shown. Our long-term goal is to develop immunotherapy combinations that avoid this problem through rational sequencing of immunotherapy with other anti-cancer agents to enhance tumor destruction and improve patient survival. Based on our preliminary data, we hypothesize that serial combination immunotherapy utilizing anti-PD-1 and anti-angiogenesis therapy with immunomodulatory chemotherapy in a predefined sequence leads to meaningful improvements in clinical outcomes in association with disruption of the immunosuppressive tumor microenvironment and promotion of antitumor systemic immune responses. To test this hypothesis, we will perform a phase II trial to determine the therapeutic efficacy of serial combination immunotherapy and examine its impact on local and systemic immune responses in patients with mGEA through the following specific aims: Aim 1 will determine the therapeutic efficacy of serial combination immunotherapy in patients with metastatic GEA. Aim 2 will interrogate patient samples collected longitudinally from the parent trial to identify the impact of serial immunotherapy on immunosuppressive, antitumor, and angiogenic components within the tumor environment, including tumor- related local and systemic immune responses. Our expected outcomes are to show improved clinical efficacy using an innovative immunotherapy combination in which PD-1 blockade is delivered in a predefined sequence and to gain critical knowledge on the impact of this serial immunotherapy approach on tumor-related local and systemic immune responses in patients with mGEA patients. Together, these new proof-of-concept data are expected to inform the design of future definitive clinical trials that can improve the survival of patients with immunotherapy-resistant metastatic GEA.

PROJECT NARRATIVE Metastatic gastroesophageal adenocarcinoma contributes heavily to global cancer-related death. Our project will contribute fundamental knowledge on the effectiveness of a novel serial immunotherapy combination in patients with this disease and on its biologic impact so as to further optimize this approach. Upon successful completion of this research, these findings are expected ultimately to improve the survival of patients with this disease.