PDCD1 and neoplasm: Recently, immune checkpoint inhibitors (ICIs) targeting programmed cell death protein 1 (PD-1)/PD-1 ligand-1 (PD-L1) axis and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have shown improved clinical outcomes in patients with MPM2, indicating that immune escape from host immunity is a primary mechanism of MPM tumor progression.