Peritoneal carcinomatosis of colorectal cancer is characterized by structural and functional reorganization of the tumor microenvironment inducing senescence and proliferation arrest in cancer cells

Abstract

Background: Peritoneal carcinomatosis (PC) is a terminal evolution from primary colorectal cancer (pCRC) associated with poor patient survival. Impact of the immune cell infiltrate on PC pathogenesis is unknown. Therefore, we characterized the immunological tumor microenvironment regarding proliferation, senescence and neovascularization. Methods: Formalin-fixed and paraffin-embedded (FFPE) tissue of PC and pCRC was examined by immunohistochemistry. Cells infiltrating resected tissue were isolated and analyzed by flow cytometry. PCR arrays detected the expression of genes relevant for helper T (TH) cell responses, like TH1, TH2 and TH17 response. Results: PC tumor cells demonstrate significantly lower proliferation rates than pCRC, but show significantly more senescence. PC is surrounded by significantly increased numbers of cytotoxic active Natural Killer (NK) cells, follicular helper T cells (TFH) and B cells, whereas pCRC shows more CD4+ TH cells, CD8+ cytotoxic T (TC) cells, eosinophilic granulocytes, TH17 and regulatory T (Treg) cells. PC is characterized by significantly increased interferon-γ (IFNγ), an upregulation of tumor necrosis factor (TNF) and the NK cell-regulating cytokine interleukin-15 (IL-15). An upregulation of angiogenesis-related genes, like vascular endothelial growth factor-A (VEGF-A), leads to severe neovascularization in PC. Correlations of PC results reveal that elevated numbers of interleukin-17 (IL-17) positive cells are associated with high cancer cell proliferation, whereas high numbers of IFNγ positive cells correlate with more tumor cells in senescence. Conclusion: The cellular immune reaction is modified during metastasis, inducing senescence in PC tumor cells. Immune surveillance in PC is facilitated by NK cells and high levels of IFNγ and TNF. Counteracting this effect, TFH and B cells combined with VEGF-A enhancement promote neovascularization in PC (Illustration 1).