Prognostic Impact of MLL Partial Tandem Duplication in Acute Myeloid Leukemia of Intermediate Cytogenetic Risk: A Subgroup Analysis of Cetlam Protocol 2003 & 2012

Background

Cytogenetics at diagnosis is the most important prognostic factor in acute myeloid leukemia (AML). Of note, intermediate cytogenetic risk group (IR-AML) is a very heterogeneous subset including normal karyotypes and all the cytogenetic abnormalities not included in the favorable or the adverse groups. Molecular alterations affecting NPM1, FLT3 and CEBPA show a prognostic impact in IR-AML. MLL partial tandem duplications (MLL-PTD) have also been described in this group of AML, but their prognostic impact have not been well established.

Aim

To analyze the prognostic relevance of MLL-PTD in the subset of patients diagnosed with IR-AML since 2003, and included in the CETLAM protocols LMA-2003 and LMA-2012.

Methods

Between 2003 and 2004 MLL-PTD were analyzed by Southern Blot (enzymes employed BglII, EcoRI, BamHI). Since 2004, a long PCR strategy was used to identify this abnormality.

Results

NPM1 mutations (NPM1mut), FLT3 internal tandem duplications (FLT3-ITD) and MLL-PTD were available for 893 patients. No MLL-PTD was found among 111 and 161 patients of the good and poor cytogenetic risk groups, respectively. The IR-AML group included 621 patients, and 37 carried a MLL-PTD (6%), thus only this cytogenetic group of patients was analyzed. NPM1mut were found in a 41% of patients and none of them had a concomitant MLL-PTD (p<0.001). FLT3-ITD were found in a 31% of patients, and 14 patients had also an MLL-PTD. No correlation between MLL-PTD and age, leukocyte count, and percentage of blasts in bone marrow was found. There was a significant association with gender: men were more frequently mutated than women (29 vs 8; p=0.001). Regarding outcome of IR-AML, leukemia-free survival (LFS) was significantly higher for patients without MLL-PTD (5-year LFS 44±3% vs 18±8%; p<0.001), and overall survival (OS) was also better for this subgroup of patients (5-year OS 42±2% vs 20±7%; p=0.004). There were no differences in the complete response rate, but patients with MLL-PTD had a higher risk of relapse (cumulative incidence at 5 years 39 vs 74%, p=0.000151). Among patients with MLL-PTD, no differences were observed depending on the concurrence of FLT3-ITD. When only patients with NPM1 wild-type were considered, MLL-PTD maintained a significantly poor prognostic impact (36±3% vs 21±7%; p=0.009).

Conclusions

MLL-PTD is a genetic alteration found in a 6% of IR-AML. Patients with this abnormality have a worse LFS and OS than the rest of patients of the IR-AML group.

Based on these results, patients with MLL-PTD should be considered as patients with poor cytogenetic risk AML for treatment allocation.