PB1690 ACUTE MYELOID LEUKEMIA WITH “CUP‐LIKE” BLASTS – ASSOCIATION WITH NPM1 AND FLT3 MUTATIONS AND IMMUNOPHOTYPIC FEATURES
Authors: Silva M. , Sthel V. , Vescovi M. , Sandes A. , Barroso R. , Kimura E. , Barbosa M. , Chaufaille M. D. L. , Pesquero J. , Yamamoto M. 
Published: June 2019

Background:

The diagnosis and classification of acute myeloid leukemias (AMLs) are based on morphologic, cytogenetic and molecular findings. AMLs with “cup‐like” (CL) morphology have been associated with a high frequency of FLT3‐ITD and NPM1 mutations.

Aims:

The aim of this study was to evaluate the relation of CL morphology with the most important prognostic markers for AML and immunophenotypic features.

Methods:

74 patients [M/F = 1, median age 60.5 years (17‐88)] consecutively diagnosed with non‐FAB‐M3, M4 or M5 AMLs that had available FLT3 and NPM1 mutational status were included. CL morphology was defined as a dim colored invagination, resembling a cup or pocket shaped, measuring ≥25% of the nuclear diameter. Two independent examiners, after counting 200 blasts on peripheral blood or bone marrow slides, determined the % of CL blasts (discrepant counts were settled with the aid of a third examiner). The results were then compared with clinical, laboratory, immunophenotypic, cytogenetic [G Band Karyotype(KT)] and molecular (FLT3‐ITD and NPM1) findings obtained at diagnosis. CL % were classified into 3 groups: A(<5%), B(5‐9%), C(≥10%). Statistical analysis with T‐Student, X2 and Fisher exact tests were performed.

Results:

CLs varied from 0‐30%; 63 patients (85%) had <5% (group A); 4 (5,4%) were B and 7 (9%) had ≥10% (C). Group C patients were mostly female (5 of 7). Median white blood counts were higher in group C (69x109/L, range 1.9‐202x109/L) vs B (22.7 × 109/L, range 12‐28.4 × 109/L) vs A (12.8 × 109/L, range 1.2 ‐212 × 109/L) (CxA p = 0.002). Immunophenotyping studies showed that cases with higher CL percentages were less likely CD34 positive: [C (1 of 7) vs B (100%, 4/4) vs A (77%, 48/62) (CxA, p < 0.002)] and that they also tended to be more likely HLA‐DR negative [C (3/7) vs B (4/4) vs A (47/54), (CxA, p = 0.06)]. KTs were normal in 16/45 of group A, 2/4 of group B and in 1/3 of group C. FLT3‐ITD was present in 15% (11/74) of this cohort. These mutations were most frequent in group C [(3/7, 43%) vs. B (1/4, 25%) vs A (7/63, 11%) (CxA p = 0.055)]. NPM1 mutations were identified in 12/70 (17%) of the cases. These mutations were also more frequent in group C [6/7; 85.7%) vs B (0/4) vs A (6/59, 10%), (CxA/B p < 0.001)].

Summary/Conclusion:

It is important to rapidly identify features related to cytogenetic and molecular abnormalities in patients with AML. Thus, a morphological evaluation is an important step of acute leukemia diagnosis. Previous studies had reported the association of CL morphology with higher blood counts, a more mature immunophenotype (negativity for CD34 and HLA‐DR), normal KT and FLT3‐ITD/NPM1 mutations. Notably in our study, these associations were only statistically significant when CLs were >10% of the blasts, with the exception of normal KT (probably due to the small number of evaluable cases). Curiously, at least in 3 other studies, CL morphology was also more frequent in females. Recent studies using electron‐microscopy have demonstrated mitochondrial accumulation at the CL region which could be related to the pathogenesis of theses AMLs. In summary, identifying CL morphology is not difficult, and our study can validate a method to predict phenotypic features and NPM1 mutations with a high degree of confidence.