For this patient, there was no known genetic predisposition syndrome, the BCP-L was negative for KMT2A rearrangements, and the ALL and BCP-L showed different B-cell receptor gene rearrangement, although both tumors had t(12;21), hence the possibility of late relapse of t(12;21) ALL could not be entirely excluded. The gene discussed is KMT2A; the disease is acute lymphoblastic leukemia.