Revisiting Cytochemical Myeloperoxidase (MPO) Stain for Early Diagnosis of Acute Promyelocytic Leukemia (APML) in Areas with Limited Resources: An Experience from a Tertiary Care Center in India

Abstract

Introduction- Acute Promyelocytic leukemia (APML) needs to be suspected early so that All-Trans Retinoic Acid (ATRA) therapy can be started as soon as possible. Flow cytometry shows absence of CD34 and HLADR in most cases and so can aid in diagnosis along with the usual morphological clues. However, it may have confusing patterns as in hypogranular APML and sometimes may be positive for HLA- DR and CD34. RT-PCR for detection of characteristic APML translocations (t(15;17),t(17;17) and others) is gold standard for APML diagnosis which is time consuming and often not possible especially in resource limited areas. Cytochemical MPO stain is a robust laboratory test that can be a valuable aid to morphology in early diagnosis of APML. In this study, the role of cytochemical MPO was evaluated for early diagnosis of APML.Method- This study included all the cases of APML that were diagnosed in a tertiary care center in India from May 2011 to May 2014. Cytochemical stains (MPO, Non- specific Esterase (NSE), Periodic- acid Schiff (PAS) stains were performed on peripheral smear and bone marrow aspirates. Flow cytometry was performed on peripheral blood/bone marrow aspirate in EDTA on Beckman Coulter Flow Cytometer (FC500) using a panel of markers. RT-PCR was not available. However, all the above cases responded immediately to trial of ATRA (diagnosis confirmed by response to treatment trial with ATRA). The study was approved by Institutional Ethics committee.Results & Discussion- 13 cases of APML (6 males, 7 females) were identified with age ranging from 2-36 years. On flow cytometry, side scatter was moderate in 4 cases and high in 9 cases. The former were AML M3v (hypogranular variant) whereas the latter were classic APML. CD13 was heterogeneously dim to moderate positive in 12/13 cases .CD 33 was homogenously positive in all 13 cases (dim positive in 3; moderate positive in 10). CD34 was positive in 1/13 case and HLA-DR was positive in 2/13cases. All cases showed 3+ cytochemical MPO positivity, diffuse flush PAS positivity and NSE positivity. All cases went into immediate remission on treatment with ATRA.Thus even though flow cytometry was helpful in diagnosing APML, there were still some variations in the patterns. It is concluded that, though flow cytometric pattern of APML is often characteristic, occasionally it may have moderate side scatter and positive HLA-DR and CD34. In such situations and also in places with limited availability of flow cytometry/ RT PCR , strong (3+) cytochemical MPO staining in addition to characteristic morphologic features helps in the quick suspicion of APML and early treatment trial with ATRA. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.