JAK2 and acute lymphoblastic leukemia: These observations prompted us to describe a group of Mexican children with B‐ALL and recurrent gene fusions, searching for CRLF2 rearrangements and overexpression, dominant‐negative IKZF1 isoforms (Ik6, Ik8, and IKZF1a), and surrogate markers for Jak2, ABL, and Ras signaling pathways.