MUTATIONS OF ASXL1 GENE IN PATIENTS WITH AML WITH AN INTERMEDIATE-RISK CYTOGENETIC PROFILE

ABSSUB-5208

Background: ASXL1 is a highly conserved protein which belongs into the ETP (enhancer of trithorax and polycomb) protein family which functions as an epigenetic regulator of gene transcription through the changes in the chromatin structure. ASXL1 gene is located in the chromosomal region 20q11.21, comprises 12 exons and encodes a nuclear protein of 1541 amino acid residues. Its mutations (particularly found within exon 12) were described in patients with various kinds of myeloid malignancies including AML and MDS.

Aims: We attempted to test the prognostic impact of ASXL1 mutations in our patient cohort.

Methods: RNA for ASXL1 mutation analysis was available from 226 patients with AML with an intermediate-risk cytogenetic profile (defined according to Grimwade et al., Blood, 2010) diagnosed at a single institution between years 1998-2011. Median age at diagnosis was 55.1 years (range 18.1-81.7), the initial median WBC count was 23.1 x 10⁹/L (range 0.4-483.7). The male/female ratio was 109/117 and the median of follow-up was 13.0 months.

The whole exon 12 was amplified using 4 RT-PCR reactions; PCR products were treated by ExoSAP-IT reagent and directly sequenced. Potential polymorphisms were excluded by analyzing either remission samples or DNA isolated from patients’ nails.

Results: ASXL1 mutation was detected in 26 from 226 patients (11.5%). We identified 6 different frameshift changes, 5 nonsense and 4 missense mutations; in one patient we found two different mutations. Another 5 various missense mutations were found out to be polymorphisms. Only 4/26 (15.4%) patients harboured ASXL1 mutation together with FLT3/ITD, which is the most frequent aberration in AML with intermediate prognosis, while amongASXL1-negative cases it was 68 from 200 (34.0%) (P=0.028). Presence of ASXL1 mutations was not influenced by the occurrence of DNMT3A mutations. Patients carrying ASXL1 mutation had significantly lower WBC counts (26.4 vs. 3.5 x 10⁹/L; P=0.002) and lower percentage of blasts in bone marrow at diagnosis (44.1% vs. 70.0%; P=0.009). Mutations of ASXL1 slightly decreased the chance to reach complete remission (CR): only 13/25 (52.0%) ASXL1-positive cases receiving standard induction treatment achieved CR compared to 125 from 185 (67.6%) patients without this aberration (P=0.062). The initial positivity of ASXL1 had no impact either on the relapse rate (38.5% with mutated ASXL1 relapsed similarly as 48.8% patients without it; P=0.239) or on the relapse free survival in patients who reached CR. Presence of ASXL1 mutation did not influence overall survival (OS) of patients as well (P=0.770).

Summary/Conclusion: We detected ASXL1 mutation in almost 12% of patients with intermediate-risk cytogenetics, mainly in those lacking FLT3/ITD. ASXL1-positive patients had lower WBC counts and lower CR rate which is in concordance with results published so far. Although missense mutations are often considered as polymorphisms, we identified 4 missense changes that turned out to be true mutations (disappearing when patients achieved CR and not detectable in nails’ DNA). We did not prove any impact of the ASXL1 positivity on the incidence of relapses as well as on OS. The presence of ASXL1 mutations did not substantially worsen the prognosis of patients.

Keywords: AML, Mutation, Prognosis

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