It is important to ensure that a blast crisis of chronic myeloid leukemia with an MPAL immunophenotype, post-cytotoxic therapy leukemia with an MPAL immunophenotype, and MPAL that has acquired BCR::ABL1 secondarily is not miscategorized as de novo MPAL with BCR::ABL1 fusion. The gene discussed is ABL1; the disease is leukemia.