Flow cytometric pattern of acute promyelocytic leukemia with aberrant expression of CD79a

Abstract

Background: Acute promyelocytic leukemia (APML) is a subtype of acute myeloid leukemia seen mostly in young patients with an aggressive disease course and a tendency towards life-threatening disseminated intravascular coagulation (DIC), requiring prompt diagnosis and specific early intervention. The molecular hallmark of APL is t(15;17)(q22;q21) PML-RARA, and serves as the molecular basis of the highly effective therapy with all-trans retinoic acid. Flow cytometric (FCM) immunophenotyping facilitates a rapid diagnosis and subtyping of acute leukaemia and is critical in the management of patients with APML. Objectives: We analyse and describe the flow cytometric pattern of 5 cases of APML and describe the aberrant expression of CD79a, a hitherto B-cell lineage marker. Methods: Six-colour FCM analysis of bone marrow aspirate was performed for all cases. Trephine biopsies of all the cases were analysed for expression of CD79a primary antibody, SP18 clone; Ventana, Tucson, USA. Karyotypic analysis was also done. Results: Classic APL has a well-recognized flow cytometric pattern with increased side scatter, lack of expression of HLA-DR, CD11a, CD11b, CD18, positive CD117, negative or weakly positive CD15 and CD65, negative CD34, often positive CD64, variable (heterogeneous) CD13 and bright CD33.Four of the five cases were observed to aberrantly express CD79a. Conclusion: APL cases can be rapidly identified by FCM using a routine screening panel. CD79a aberrant expression in AML, either on IHC or on FCM, is strongly suggestive of a diagnosis of APML.