A study examining 45 FDA ICI approvals between 2011 and 2019 across 15 tumor types found that PD-L1 expression was predictive of response to PD-1/L1 ICI in only 28.9% of cases (245), suggesting the complexity and difficulty of identifying putative protein and epigenetic markers for patient stratification and potential therapeutic targeting. The gene discussed is PDCD1; the disease is neoplasm.