GZMB and neoplasm: For PD-1/PD-L1 Inhibitors monotherapy, key predictive biomarkers encompass both tumor burden—mainly reflected by tumor markers [23, 24], CTCs [38–40], PD-L1+ CTCs [43, 44], and ctDNA [26, 31]—and immune cell subsets that exhibit either cytotoxic potential, such as CD103+PD-1+CD8+T cells [86], GZMB+MAIT and IFN-γ+MAIT cells [123], NKT cells [125, 126], and CD56dimCD16+NK [148, 149] cells, or immunosuppressive/exhausted phenotypes, including CD73+PD-1+CD8+T cells [89], PD-1+Eomes+CD8+T cells [90], Tregs [109], IL-17A+ MAIT cells [123], and inhibitory myeloid populations [154].