Given that multiple studies in a variety of tumors have demonstrated a positive correlation between PD-L1 expression and response to ICIs or OS, even in first-line combination therapy [63–65], pembrolizumab is currently approved by the FDA for use in patients with PD-L1+ (PD-L1 ≥ 50% of tumor cells in first-line treatment and ≥ 1% in second-line treatment) NSCLC and PD-L1 immunohistochemistry (IHC) as a companion diagnostic for anti-PD-1 therapy in NSCLC patients [66, 67]. The gene discussed is PDCD1; the disease is non-small cell lung carcinoma.