PDCD1 and pancreatic neoplasm: Finally, pancreatic cancer cells express cytotoxic-T-lymphocyte associated protein 4 (CTLA-4) and the ligand for programmed cell death protein-1 (PD-1), PD-L1 [32], which is activated by the EGFR/MAPK pathway from myeloid cells [33], inhibiting T cell function.