Characterization of Tumor Immune Microenvironment in Peritoneal Carcinomatosis treated with Cytoreductive Surgery and HIPEC

Peritoneal carcinomatosis is characterized by the dissemination of tumor cells within the peritoneal cavity. The immune microenvironment in peritoneal carcinomatosis is notably intricate and exhibits significant inter-patient variability. Influencing factors of the immune response in the peritoneal cavity include cancer type and stage, the presence of immunosuppressive cells, and the expression of immune checkpoint molecules. Despite the recognized complexity, there remains a paucity of research dedicated to comprehensively characterizing the immune microenvironment in this context. The objective of this study was to characterize the immune infiltrate in patients with peritoneal carcinomatosis secondary to gynecologic cancers and Pseudomyxoma Peritonei, who underwent Cytoreductive Surgery (CRS) in conjunction with Hyperthermic Intraperitoneal Chemotherapy (HIPEC), the primary therapeutic strategy for this condition.Our analysis revealed an enrichment of T and B cells in pre-treatment samples. Moreover, in 50% we detected a tendency to form microaggregates resembling tertiary lymphoid structures within the stroma. Additionally, we observed increased expression of PD1 and PD-L1 within these structures. In post-treatment biopsies we observed a decrease of cellular density of immune cells, except for pro-tumoral M2 macrophages.Further studies involving a larger cohort of cases are needed to investigate the immune microenvironment in peritoneal carcinomatosis in order to identify a potential prognostic and predictive biomarkers in both gynecologic cancers and Pseudomyxoma Peritonei.