JAK1 and neoplasm: Although cell‐line‐derived xenograft models have the advantage to study tumors of human origin, a major drawback of these models is the absence of a functional immune system.36 However, this is a critical factor in our study, since ruxolitinib was reported to promote immunosuppression and could thereby eventually enhance tumor progression.18 Thus, we addressed the effects of JAK1/2 inhibition in fully immunocompetent mouse models of autochthonous K‐RAS‐driven lung AC.