JAK1 and neoplasm: 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).