JAK2 and neoplasm: In this regard, the mouse Pax5Jak2/+ tumor model differs from the human PAX5‐JAK2+ B‐ALLs, as the Pax5Jak2 allele was created by an in‐frame insertion of the partner Jak2 cDNA sequences into the mouse Pax5 locus, whereas the human PAX5‐JAK2 rearrangements are generated by fusion of the 5’ part of the PAX5 locus with the 3’ region of the JAK2 locus (Nebral et al, 2009).