Cytological and molecular characterization of a MPO-negative APL. (A) May Grünwald Giemsa staining of a blood smear showing medium-sized myeloid blasts without granulation or Auer rods. (B) Cytochemical evidence for MPO negativity of blast cells (as compared with neutrophils; arrows). (C) Molecular evidence of the t(15;17) translocation by fluorescent in situ hybridization showing double fusion signals in blast cells (arrows). (D) Single nucleotide polymorphism analysis showing a uniparental disomy of the long arm of chromosome 17. Original magnification ×400 for panels A-B.