PDCD1 and neoplasm: With the development of immunotherapy, namely immune checkpoint inhibitors (ICIs) such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), and programmed death ligand 1 (PDL-1) PDL-1 inhibitors, several markers have also been studied in assessing tumor response.