Somatic mutations of JAK3 alleles have also been identified in cancer cell lines, as well as in patients with the following diseases: acute megakaryoblastic leukaemia,14, 15 high‐risk childhood ALL,16, 17 Down syndrome AML and ALL,18 T‐cell ALL19 and cutaneous T‐cell lymphomas.20 Here, JAK3 is linked to acute lymphoblastic leukemia.