In some cancers such as fibrosarcoma and acute lymphoblastic lymphoma, JAK1 mutations activate JAK–Signal transducer and activator of transcription (STAT)–interleukin-6 signaling to promote tumor cell proliferation (25, 26) whereas in most other cancers, JAK1 mutations impair interferon (IFN) signaling and induce immune resistance (27–29). This evidence concerns the gene JAK1 and fibrosarcoma.