Blasts were negative for myeloperoxidase (MPO), and immunophenotype by flow cytometry was consistent with pre-B cell acute lymphoblastic leukemia (ALL) (positive for CD10, CD19, CD34, HLA-DR, and TdT, negative for CD3, CD5, CD7, and myeloid antigens). This evidence concerns the gene MPO and B-cell acute lymphoblastic leukemia.