Here, we successfully established for the first time, to our knowledge, a RASmut BCP-MLL-AF4 positive leukaemia cell line and we showed that the allosteric MAP2K inhibitor PD032590149 at nanomolar concentration reduced the RASmut MLL-AF4+ B cell line proliferation to 40% without any significant effect on RASwt MLL-AF4+ B cell lines even at micromolar concentration, suggesting to evaluate RAS-pathway inhibition by PD0325901 in MLL-AF4+ RASmut specimens in preclinical studies. This evidence concerns the gene AFF1 and leukemia.