Interleukin-7 (IL7) signaling activating mutations affect about one-third of T-ALL patients [8, 27] and occur in every component of the signaling pathway: the receptor α-chain IL7R, kinases JAK1 and JAK3 or the transcription factor STAT5 and the subsequent pathway activation can be inhibited by JAK-inhibitors [28, 29]. The gene discussed is IL7R; the disease is acute lymphoblastic leukemia.