STAT1 and neoplasm: Furthermore, cytokines within the tumor microenvironment, especially IFN-γ, which signals through the Janus kinase/signal transducer and activator of transcription 1/interferon regulatory factor 1 (JAK/STAT1/IRF1; encoded by JAK, STAT1, and IRF1) pathway, and interleukin-6 (IL-6; encoded by IL6), which signals through the JAK/signal transducer and activator of transcription 3 (STAT3; encoded by STAT3) pathway, induce the expression of PD-L1.