Immunosuppressive Environment of Pancreatic NENs—A Review

Pancreatic neuroendocrine neoplasms (pNENs) are rare tumors with significant biological diversity. Despite significant improvements in diagnostics and a growing range of available therapies, long-term disease control remains difficult in advanced cases. The tumor microenvironment, which in pNENs adopts a predominantly immunosuppressive profile and promotes tumor development, is attracting increasing attention. A complex network of interactions dominates the tumor tissue, including M2 macrophages, regulatory T cells, and numerous pathways that inhibit effector lymphocyte activity. M2 macrophages, through the secretion of anti-inflammatory cytokines and exosome-mediated signaling, support angiogenesis while simultaneously attenuating the cytotoxic response. Simultaneously, receptors and ligands associated with immune checkpoints are overexpressed. In addition to classic molecules such as PD-1/PD-L1 and CTLA-4, the role of B7x and CD276 is increasingly being emphasized, as their presence correlates with rapid disease progression and poor prognosis. To date, attempts to use checkpoint inhibitors as monotherapy have yielded modest clinical benefits. However, approaches based on combination strategies—both in the form of dual immune blockade and in combination with chemotherapy or angiogenesis-targeted therapy—have shown significantly greater activity. Therapies using tyrosine kinase inhibitors, such as sunitinib and newer drugs (lenvatinib, surufatinib, cabozantinib), may partially normalize the tumor’s disrupted vascular architecture and thus increase its susceptibility to immunological interventions. In the coming years, it will be crucial not only to overcome the immunosuppressive nature of the TME but also to identify predictive biomarkers that will allow for more precise patient selection. This approach may open the way to more effective, personalized therapies for pNENs.