CD33 and mixed phenotype acute leukemia: To confirm the myeloid component of MPAL, myeloperoxidase (MPO) is the single most specific hallmark, but due to technical factors associated with MPO measurement, a diagnosis of MPAL necessitates additional criteria as: expression of myeloid antigens such as CD117, very bright CD13 and CD33, expression of monocytic markers or heterogeneity of antigen expression (Borowitz et al., 2017b).