Within metastatic cSCC, inhibitory receptors (and potential markers for exhaustion) including Tim-3, cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4), and programmed death-1 (PD-1) are frequently found on CD8+ T cells [97]—the presence of their ligands within cSCC, specifically PD-L1, is associated with poorer outcomes [98]. This evidence concerns the gene CTLA4 and skin squamous cell carcinoma.