Gain-of-function mutations in JAK3 and JAK1 [42,128,129], as well as in STAT5 gene [130,131] have been detected in a variable fraction of T-ALL patients, along with a rare t(9;12)(p24;p13) translocation driving the expression of a constitutively active fusion protein ETV6-JAK2 [132,133]. The gene discussed is JAK2; the disease is acute lymphoblastic leukemia.