Leukemic blasts with extensive marrow infiltration were partially positive for cytochemical peroxidase staining (20–30%), while Auer rods were absent, and immunophenotypic characterization confirmed co-existence of a myeloid CD34+, CD117+/−, HLA-DR+, cyMPO+/−, CD13+, CD33+, CD36+, CD71+ blast population negative for CD3-, cyCD3, CD19 and CD79a alongside a CD19+, CD22+/−, cyCD79a+, nuTDT+ und cyCD3- B-lymphoid blast population consistent with mixed phenotype acute leukemia (MPAL type B/myeloid) according to WHO criteria. Here, CD22 is linked to acute leukemia.