AFF1 and acute lymphoblastic leukemia: Response and MRD rates are further dependent on the partner gene involved in the translocation with KMT2A; the Ponte di Legno Childhood ALL Group study of KMT2A-r pediatric ALL, showed MRD negativity rate of 51% in (4;11)(q21;q23)/KMT2A::AFF1 rearrangement compared to 75% in t(10;11)(p12;q23)/ KMT2A::MLLT10.5