PDCD1 and skin squamous cell carcinoma: Immune checkpoint inhibitors (ICIs), such as anti-programmed cell death 1 (PD1) antibodies (Abs) and anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA4) Abs, have been widely administered for not only advanced melanoma [1,2], but also various non-melanoma skin cancers [3] such as advanced cutaneous squamous cell carcinoma (cSCC) [4], advanced basal cell carcinoma (BCC) [5], cutaneous T cell lymphomas (CTCLs) [6,7], and cutaneous angiosarcoma (CAS) [8].