Regarding the setting of refractory/relapsed AML patients, there is a risk of onset of leukemic clones with multiple adverse-risk genetic mutations (including FLT3-ITD) or the presence, at relapse, of an allelic burden higher than that at diagnosis, capable of negatively influencing the prognosis, unlike the diagnosis, where there is a greater probability of facing a polyclonal disease [55,56,57,58,59,60]. This evidence concerns the gene FLT3 and acute myeloid leukemia.