AFF1 and acute lymphoblastic leukemia: Although sequencing studies have confirmed a silent mutational landscape for infant MLL-AF4+ ALL, RAS-activating mutations are detected frequently and have been associated with a poorer prognosis and with extramedullary leukemia in mouse models; however, the presence of RAS mutations does not appear to be required, and they are often subclonal and absent at relapse (Agraz-Doblas et al., 2019; Andersson et al., 2015; Prieto et al., 2016).