Introduction: Pancreatic cancer (PC) is a hard-to-treat malignancy characterized by its highly aggressive tumor biology and a strongly immunosuppressive tumor microenvironment. Due to its characteristics, immune checkpoint inhibitors, such as anti-PD-1 antibodies, have yielded limited outcomes in this disease. Targeting DNA damage repair pathways has shown to improve tumor immunogenicity, potentiating immunotherapy efficacy. BBIT20, a monoterpene indole alkaloid derivative, is a first-in-class inhibitor of the homologous recombination DNA damage repair pathway. This work used a syngeneic model of PC to explore the potential of BBIT20 to inhibit tumor growth by promoting immune-mediated responses, alone or in combination with anti-PD-1 immunotherapy. Methods: KPC cells were injected subcutaneously into C57BL/6J mice, which were then treated with a vehicle, BBIT20 (2 mg/kg), anti-PD-1 (100 μg/animal), or both. Tumor progression was monitored by caliper measurements, and tumors were collected at the experimental endpoint. PD-L1 expression and levels of inflammatory mediators and immune cell populations, including cytotoxic T lymphocytes and macrophage subsets were assessed by immunohistochemistry. Results: BBIT20 reduced disease progression while anti-PD-1 alone produced only a modest inhibitory effect, when compared with vehicle-treated animals. The combination of both agents significantly enhanced the antitumor response, indicating a synergistic effect relative to each treatment alone. Immunohistochemical analyses are currently being conducted to investigate treatment-associated alterations in immune cell activation and infiltration within PC tumors. Quantification of PD-L1, CD8, and CD206, and additional markers is in progress, with BBIT20-treated tumors exhibiting decreased PD-L1 expression. Conclusions: BBIT20 revealed a synergistic effect with anti-PD-1 in PC, potentiating tumor growth inhibition and reducing PD-L1 expression. These findings support the ability of BBIT20 to improve immunotherapy efficacy in PC through immune-stimulating activity. Acknowledgments:This work received support from the PT national funds (FCT/MECI) through the project 2024.13556.PEX (https://doi.org/10.54499/2024.13556.PEX).