STUDY OF THE ASSOCIATION OF NG2 EXPRESSION IN ACUTE LYMPHOBLASTIC LEUKEMIA WITH MLL GENE REARRANGEMENT

Abstract

SUMMARY A LL is the most common malignancy diagnosed in patients younger than 15 years, accounting for 23% of all cancers and 76% of all leukemias in this age group. It accounts for only 20% of adult acute leukemias (Pui, 2010.) Because leukemic lymphoblasts lack specific morphologic and cytochemical features, immunophenotyping is an essential part of the diagnostic evaluation (Pui and Evans, 2006). Cytogenetic analysis of leukemic cells is the cornerstone for the prognostic stratification of ALL patients at the onset of disease because they are independent factors in predicting clinical outcome of patients and determining the duration and type of treatment (Inaba et al., 2013). Rearrangements involving the myeloid–lymphoid lineage gene on chromosome band 11q23 are frequent cytogenetic events in both lymphoid and myeloid leukemia (Emerenciano et al., 2011). Currently the used methods to detect MLL rearrangements include conventional cytogenetics, fluorescence in situ hybridization and reverse transcription-PCR analyses. Due to the fact that MLL-r detection using standard techniques can be costly and requires specialized skills, a rapid and cost-effective technique would be quite useful especially for developing countries and worldwide efforts have focused on achieving high sensitivity and specificity values using Flow cytometry to identify MLL-r (Emerenciano et al., 2011). With the discovery in humans of a homolog of the cell surface chondroitin sulfate NG2 molecule in rats, previous groups have reported that MLL-r may be predicted through the cell surface recognition of NG2 using the monoclonal antibody (MoAb) 7.1. The mechanisms underlying this association are still being examined and a lack of association has been reported in certain cases (Emerenciano et al., 2011). The aim of the present work was to evaluate the role of NG2 as a tumor marker in ALL and its predictive value in MLL gene rearrangement. To achieve this aim FISH technique was carried out on all patient samples, MLL gene rearrangement was detected in eight patients with childhood ALL (26.7%), 4(50%) of them were infants. Six(75%) of MLL positive patients were NG2 positive while 2 patients (25%) were NG2 negative. By immunophenotyping, NG2 was positive in 7 patients. 1 patient showed NG2 positive in absence of MLL-r. However MLL gene duplication was detected By FISH indicating positive correlation between MLL-r and NG2 expression. NG2 expression was positively correlated with MLL gene rearrangement and was associated with poor prognostic factors including younger age (4 cases were infants), CNS infiltration (28.6%), and leukocytosis. Roc curve was used to detect the best cut off value of NG2 positivity for prediction of 11q23 break apart (MLL gene rearrangement). We calculated the sensitivity, specificity and positive predictive value of NG2 in predicting MLL rearrangement in our patients. NG2 showed a sensitivity of 75%, specificity of 95%, positive predictive value of 85.7% and accuracy of 90% in predicting MLL rearrangement. We can conclude that a highly significant correlation was found between NG2 expression and MLL gene rearrangement. Moreover, NG2 expression was associated with other poor prognostic factors in our studied ALL patients including; younger age group (50% infants), presence of leucocytosis, presence of CNS infiltration (50% of NG2positive patients), and the poor cytogenetic aberration 11q23 break apart (MLL-r). NG2 percent expression by IPT ≥ 18.6% was the best cut of value to be used as a significant predictor of MLL-r by FISH technique with sensitivity 75% and specificity 95%. So our results suggest that immunophenotyping is a reliable approach to predict MLL-r using flow cytometry technique on NG2 antigen data, and so we can predict the aggressive clinical presentation and other poor prognostic factors associated with this type of leukemia.