In five independent studies on different tumor types with 115 patients defined as responders to PD-1/PD-L1 blockade (i.e., patients with durable clinical benefit, complete response, or partial response according to the response evaluation criteria in solid tumors (RECIST) v1.1), seven patients (6.1%) had a missense or nonsense mutation in IFN-γ signaling: one patient in Ifngr1 and JAK-2, one in JAK-1, and five in JAK-2 [42,43,44,45,46]. The gene discussed is JAK2; the disease is neoplasm.