Analysing "tear-drop" prints of acute promyelocytic leukemia (APML): immunophenotypic prognostication of APML by FCM.

Introduction: Acute promyelocytic leukemia (APML), although genetically and morphologically distinct from other AML (acute myeloid leukemia) subtypes, is one of the most best responsive acute myeloid leukemia. -Conventional diagnostic methods and morphological hints often fail in the majority of the cases in the peripheral laboratories owing to resource constraints, unavailability of cytogenetic work-up, hypogranular variants, morphological mimicry by AML-monocytic and myelo-monocytic, etc. Flowcytometry (FCM), however, can be utilized as a feasible and reliable immunophenotypic diagnostic and prognostic tool for prompt identification of APML. In order to rapidly and sensitively diagnose APML we intended to suggest a cost effective, sensitive FCM panel and also to prognositicate patients.

Material and methods: In this retrospective study, flowcytometry characteristics of 123 cases of acute promyelocytic leukemia were studied including 40 hypogranular variants. The expression of markers was compared with the Mean flurescent Intensity (MFI) and percent expression of markers. A non-statistical comparison was made with cases of acute monocytic leukemia. The cases were grouped according to their immunophenotype characteristics and expression with comparison of MFI by multivariate logistic regression. The aberrant markers positive at diagnostic and remission flow test were compared with the survival outcomes, and their positive predictive values were calculated.

Results: The most common feature of side scatter property was the absence of blasts in the window and high side scatter, except hypogranular variants which had low side scatter. Immunophenotypically characterised by positivity for CD117, cMPO, and bright CD33 and CD13 positivity and lack of CD34 and HLA-DR was seen in the majority of APML including hypo-granular variant. We suggest a rapid diagnostic four-tube panel for fast and rapid diagnosis of APML, including hypogranular variants with 100% sensitivity. The study also identified six groups of immunophenotypes with significant prediction values of APML, including hypogranular variants. The study also highlights CD2, CD56, and CD9 as prognostic markers for acute promyelocytic leukemia.