Focal Positivity for Non-Specific Esterase in AML: A Surrogate Marker to Predict AML with t(8;21)/RUNX1-RUNX1T1
Authors: Parmentier Stefani , Birninger Nicole , Oelschlägel Uta , Mohr Brigitte , Schaich Markus , Kroschinsky Frank , Thiede Christian , Ehninger Gerhard 
Published: October 2019

Abstract
Abstract 2534
Introduction Cytomorphological evaluation of bone marrow remains a fast and easy accomplished tool in patients with suspected acute myeloid leukemia (AML). Some cytogenetic aberrations can be predicted by specific morphological features like abnormal eosinophils associated with inv(16)/t(16;16) and faggot cells with t(15;17). But implementations of cytogenetic and molecular tests nearly diminished the interest in studying cytomorphological features that might be associated with chromosomal aberrations. Common morphological characteristics often found in AML associated with t(8;21) are large blasts with abundant basophilic cytoplasm, containing numerous azurophilic granules, perinuclear clearing or hofs and single long and sharp Auer rods. But not all AML with t(8;21) show these characteristic signs. During our cytomorphological review for patients with AML within the German prospective multicenter randomized AML96 and AML2003 trials we observed that a focal non-specific esterase stain for blasts in t(8;21) appears to be another specific feature for this subentity. With this study we tried to analyze its predictive value for this chromosomal aberration.

Materials and methods
Bone marrow (BM) aspirates and peripheral blood smears of 156 eligible patients from the Study Alliance Leukemia (SAL) AML96 and AML2003 trials were investigated by conventional cytochemical methods (May-Giemsa, myeoloperoxidase, alpha-naphthyl butyrate esterase and iron staining). AML classification was performed according to FAB and WHO 2001. Diagnosis of t(8;21)/RUNX1-RUNX1T1 was made by FISH, chromosomal banding and RT-PCR analysis. Bone marrow samples from patients with AML associated with t(8;21)/RUNX1-RUNX1T1 were evaluated and reviewed by an independent and experienced morphologist. Blast morphology was evaluated for granulation, perinuclear clearing or hofs, focal positivity for non-specific esterase (NSE) and the presence of Auer rods, pseudo-Pelger neutrophils and eosinophils. Besides that we investigated its correlation for aberrant expression of CD19 and CD56 in immunophenotyping and the KIT exon-17 mutation. All statistical calculations were performed using the software program PASW statistics 17 (SPSS, Chicago, IL, USA) and R 2.10.1 (The R Foundation for Statistical Computing, 2010).

Results
Of 156 eligible patients, 72 did not have adequate bone marrow samples to assess the amount of blasts with NSE positivity; therefore, the final study cohort consisted of data sets from 84 patients. The median age was 44 years (range, 19–85 years). The distribution of gender was 39 women (46%) and 45 men (54%). The majority of cases (81%) were subclassified in FAB M2. Cytomorphology showed a focal NSE positivity in 82 patients (98% of cases). Chromosome banding analyses were performed in all cases and showed t(8;21) in all cases. Forty-three patients demonstrated additional abnormalities with 29 (35%) cases showing single additional aberrations and 14 (17%) cases having two or more additional aberrations. Focal positivity of non-specific-esterase stain was found in 25% in 11 (13%), 50% in 29 (35%), 75% in 22 (26%) and 100% in 20 (24%) of bone marrow blasts. The presence of focal NSE-positivity demonstrates a significant association with the cytogenetic aberration t(8;21) (p < 0.001). Focal NSE-positivity was present even in the absence of further morphological features associated with t(8;21). No correlation between focal NSE stain and the aberrant expression CD19 and CD56 and KIT-Mutation could be seen. In AML other than t(8;21) no focal positivity for NSE could be seen (n=100).

Conclusion
Our investigations could prove that focal positivity for NSE is a reliable surrogate marker to predict the chromosomal aberration t(8;21).

Disclosures:
No relevant conflicts of interest to declare.