Thus, the pre-treatment calculation of the percentage of biopsy tumor cells expressing the Programmed Death-Ligand 1 (PD-L1) protein, termed the tumor proportion score (TPS) for PD-L1, emerged as a clinical tool to predict efficacy of anti-programmed cell death protein 1 (PD-1) or anti-PD-L1 immunotherapy [46,47,48]. The gene discussed is PDCD1; the disease is neoplasm.