Finally, numerous potential predictive biomarkers of ICI efficacy are currently being studied: (i) T-effector and INF-γ-related gene signature [25]; (ii) peripheral blood markers such as proliferating PD-1+CD8 T cells [26] or serum interleukin-8 [27]; (iii) circulating tumor cells [28] or miRNAs/exosomes [29]. The gene discussed is PDCD1; the disease is neoplasm.