AFF1 and acute lymphoblastic leukemia: A recent study using ultra deep sequencing of 36 paediatric t(4;11) MLL-AF4 ALL found that 63.9% of them had a mutation in NRAS or KRAS that could lead to its hyperactivity [55]; however, experimental evidence suggests that these may influence the timing of disease onset and malignant cell migration, but are not required for disease initiation [56, 57], as further discussed below.