In contrast to JAK2 mutations, expression of JAK2r in primary murine pre-B cells results in cytokine-independent proliferation, suggesting that JAK2 fusion genes alone are driving genomic lesions in JAK2r ALL (Cuesta-Domínguez et al., 2012; Roberts et al., 2014a; Schinnerl et al., 2015). This evidence concerns the gene JAK2 and acute lymphoblastic leukemia.