IL21 and neoplasm: Increases in PD-L1 expression can occur on SCC cells [8] as a result of mutations in tumor cell signaling pathways or exposure of tumor cells to inflammatory cytokines IL-1, IL-6, GM-CSF, IFNγ, TNFα, and VEGF [15,16,17,18,19] and the gamma-chain cytokines IL-2, IL-7, IL-10, IL-15, and IL-21 [20].