TET2 Mutations in Secondary Acute Myeloid Leukemias: A French Retrospective Study

Abstract 176

TET2 mutations were recently involved in myeloid malignancies as in 20–26% of MDS, in 12% of MPN and in 10–17% of AML (Delhommeau et al, 2009, Langemeijer et al, 2009, Tefferi et al 2009). A link between TET2 and NPM mutations was recently highlighted in de novo AML with normal karyotype (Nibourel et al, 2009). Actually, the impact of TET2 mutations is not fully examined in secondary AML (SA). In the new OMS classification of hematological malignancies, SA are related to myelodysplasia-related changes (MRC) AML and therapy-related (TR) AML where the impact of TET2 mutations is not fully examined.

In our retrospective study, we have collected bone marrow samples from 247 patients at diagnosis identified as SA and classified according WHO. On genomic DNA, we have determined the status of TET2 as described before (Delhommeau et al, 2009) but also the status of other genes as NPM1, FLT-3, N and K-RAS, c-KIT.

According to the WHO classification, the 247 samples were subdivided in 201 MRC AML where the most of the patients had a clear previous history of haematological malignancies (MDS, MPN or MDS/MPN, n=114) and in 46 TR AML. In this cohort of 247 SA, we found 70 patients (39.5%) with a normal karyotype (NK). 69 abnormalities of the TET2 sequence were found and dispatched into 49 patients leading to 19.8% of patients with at least one TET2 mutation (29 Frameshift all inducing a premature stop codon, 24 Nonsenses, 12 Missenses in conserved regions, 2 insertions of one AA and 2 mutations of a splicing site).

The SA patients harbouring at least one TET2 mutation are older than others (64.6 years vs 71.4 years, p<0.001) and present a different pattern of biological parameters. TET2 mutation are associated with a significant higher level of Hb (9.0 vs 9.6 g/dl, p=0.01) and WBC (6.7 vs 20.3 G/L, p<0.01 with significant higher levels of PNN and monocytes). The TET2 mutated patients present also a significant lower MGV (96 vs 89.7 fl p<0.001) and a lower Platelets count (64 vs 39 G/L p<0.01). There is also a trend to a higher level of blast cells in the blood of SA patients with a TET2 mutation (29.5 vs 49.5% p=0.05) but the number of blasts in the bone marrow is unchanged (33.0 vs 32.5% p=0.57).

Cytogenetically, the patients without a TET2 mutation (n=198) present a NK in 45 cases (22.7%), an abnormal KT in 153 cases and in 57.5% (n=88) a complex KT with at least 3 anomalies. In the group of TET2 mutated patients, there is 51% of NK indicating that TET2 mutations are strongly associated with NK (p<0.001). Among the abnormal karyotype (n=24) associated with TET2 mutations, only 7 (29.1%) are complex KT with at least 3 anomalies and strikingly, only 2 patients with a TET2 mutation present a recurrent abnormality, both of them involving the chromosome 3.

When we have restricted the study of biological parameters to patients presenting a NK (n=70 with 25 TET2 mutated patients), the patients with a TET2 mutation are still older (60.5 vs 67.8 years, p<0.01) with a higher level of Hb (9.0 vs 9.9g/dl p<0.05), more WBC (5.7 vs 19.9 G/L p<0.05) and a lower level of platelets (70.0 vs 44.0 G/L p<0.05). These results suggest that the modifications of the biological parameters observed in TET2 mutated patients are not related to the NK.

Among the others molecular abnormalities tested in these 247 SA, no statistical association could be found between TET2 mutations and NPM1 mutations tested on 148 patients (p=0.071), or FLT3 abnormalities tested on 218 patients (p=0.09) or Ras mutations tested on 151 patients (N Ras and K Ras, p=0.886). However, there is a statistical association between KIT 816 mutations (determined on 156 samples) and TET2 mutations (p<0.01). When we restricted to the NK, no statistical association could be found except a slight trend to an association between TET2 and FLT3 mutations (p=0.08).

Finally and in a very interesting way, we can observe that the frequency of TET2 mutations in MRC AML is higher (22.3%) compared to the frequency established in TR AML (8.7%).

In conclusion, the SA associated with at least one TET2 mutation present a specific biological pattern, not related to a NK, and actually not understood. Moreover, considering the fact that TET2 mutations are strongly associated with NK and that the TR AML present less TET2 mutations than the others, TET2 mutations are, in these cohort, not associated with markers of poor prognosis which are complex karyotype and a previous intensive chemotherapy.