Roles of TET2 and C-CBL Mutations In the Progression of De Novo Myelodysplastic Syndrome to Acute Myeloid Leukemia

The molecular pathogenesis of myelodysplastic syndrome (MDS) and its role in the progression to secondary acute myeloid leukemia (sAML) remain to be further explored. Somatic TET2 and C-CBL mutations have recently been described in myeloid neoplasms including MDS and sAML. Most studies of TET2 or C-CBL mutations were carried out separately either at MDS or at sAML phases. There was also a discrepancy in the results of the impact of TET2 and C-CBL mutations on outcome of MDS patients.

We aimed (1) to correlate the TET2 and C-CBL mutations with clinicohematological features and outcome, and (2) to determine the role of TET2 or C-CBL gene mutations in sAML derived from MDS.

Bone marrow (BM) samples from 161 MDS patients (3 RCUD, 1 RARS, 36 RCMD, 118 RAEB, 1 MDS5q-, 2 MDS-U) at initial diagnosis were analyzed for both TET2 and C-CBL mutations; 49 of them had matched paired sAML BM samples available for comparative analysis. Mutational analysis was performed by DHPLC and/or direct sequencing of all RT-PCR or DNA-PCR products amplified with different primer pairs covering the whole coding sequences of TET2 and exons 7 to 9 of C-CBL.

The frequency of TET2 and C-CBL mutations in 161 MDS patients was 17.9 % and 1.9 %, respectively. Seven patients with polymorphism/germ line mutations or missense mutations outside of BOX 1 or 2 of TET2 gene were excluded. Of the 26 patients with 38 TET2 mutations, 14 had nonsense, 11 missense, 11 frameshift, 1 deletion, and 1 splice site mutations; 12 of them had double mutations. Three patients had C-CBL mutations (Y371S, F418S and G415S) at MDS phase. No patient had coexistence of TET2 and C-CBL mutations. TET2 mutations were significantly associated with increased risk of AML transformation (P= 0.037), whereas C-CBL mutations did not influence the risk of AML transformation (P=0.335). Patients carrying TET2 mutations had a trend of shorter time to sAML compared with those without TET2 mutations (estimated median time to sAML 8.7 months vs 15.0 months, P=0.067). Except for lower platelet count in patients with TET2 mutations (P=0.038), there were no significant differences in clinicohematological features including age, sex, hemoglobin level, white blood cell count, percentage of blasts in BM or peripheral blood, cytogenetics or IPSS (≤1.5 vs ≥2.0) between patients with and without TET2 or C-CBL mutations. No significant differences were found in overall survival with respect to mutation status of TET2 (P= 0.244) or C-CBL (P= 0.646). Of the 49 paired BM samples, 3 patients harboring C-CBL mutations at MDS phase retained the identical mutations and another 3 acquired C-CBL mutations (L370_Y371 ins L, L399V and C416W) during sAML evolution. There was an increased risk of acquiring C-CBL mutations during AML transformation (odds ratio=4.16, P=0.041), whereas TET2 mutation patterns remained unchanged and none acquired or lost TET2 mutations in sAML progression.

Our results showed an increased risk of acquiring C-CBL mutations during sAML transformation. TET2 mutations played a role as an initial event in the development of MDS in a subset of patients and were associated with more frequent and rapid sAML evolution.

Supported by grants NHRI-EX99-9711SI, NSC97-2314-B-182-011-MY3 and DOH99-TD-C-111-006.

No relevant conflicts of interest to declare.