The characteristic immunophenotypic FCM features for APL have included a high side scatter (SSC), a typical consistent expression of cluster differentiation 117 (CD117), absence of HLA-DR, and absence or downregulation of CD34 in the context of myeloid antigen expression, such as myeloperoxidase (MPO), CD33 and CD13 [10–13]. The gene discussed is MPO; the disease is acute promyelocytic leukemia.