Acute Promyelocytic Leukemia, Hypogranular Variant, with Uncharacteristic Staining with Chloroacetate Esterase

Abstract

A diagnosis of the hypogranular variant of acute promyelocytic leukemia (APLv) may be difficult to establish based on cytomorphology alone. However, the great majority of cases have a classical immunophenotype by flow cytometric immunophenotyping (FCI) (CD 13+, CD33+, dim CD64+, HLA-DR-, and CD34-) and a classical enzyme cytochemical (EC) staining pattern. [intensely staining with myeloperoxidase, Sudan Black B, and chloroacetate esterase (CAE) and negative with alpha'-naphthyl acetate and butyrate esterases]. Although the immunophenotype of APLv by FCI has varied in the literature (HLA-DR+/-and CD34+/-), the EC staining pattern has remained constant. We report a case of APLv with characteristic cytomorphology, compatible FCI data (CD 13+, CD33+, dim CD64+, HLA-DR +/-, and CD34-), chromosomal detection of t(15;17), and molecular detection of the PML/RAR alpha fusion gene; however, staining of the leukemic cells with CAE was quite uncharacteristic. We describe our findings.