Characterization of MDS Harboring TET2 Mutations and/or TET2 Deletions
Authors: Haferlach Claudia , Stengel Anna , Meggendorfer Manja , Kern Wolfgang , Haferlach Torsten 
Published: October 2019

Background: TET2 mutations and deletions have been reported in MDS. A detailed analysis of the prognostic impact of TET2 deletions and their association to TET2 mutations is lacking.
Aim: To characterize MDS with TET2 mutations (mut) and/or TET2 deletions (del) with respect to accompanying cytogenetic and molecular genetic abnormalities and their impact on prognosis.
Patients and Methods: First 788 unselected MDS cases (cohort A) were evaluated. As in this cohort only 8 cases with TET2 deletion were detected, further MDS were screened for TET2 deletions. In total 77 MDS harboring a TET2 deletion were identified and included in cohort B. Both cohorts were analyzed by chromosome banding analysis, FISH, genomic arrays and mutation analysis of TET2. Cases from cohort A were also analyzed for mutations in ASXL1, ATM, BCOR, BRCC3, CBL, CTCF, DNMT3A, ETV6, EZH2, FBXW7, IDH1, IDH2, JAK2, KRAS, LAMB4, MPL, NCOR1, NCR2, NF1, NRAS, PHF6, PRPF8, PTPN11, RAD21, RUNX1, SETBP1, SF3B1, SMC3, SRSF2, STAG2, TET2, TP53, U2AF1 and ZRSR2.
Results: In cohort A 248 cases (31%) with TET2mut were identified. TET2del and a normal karyotype were more frequent in MDS with TET2mut as compared to those with TET2 wild-type (wt) (3% vs 1%, p=0.006; 89% vs 78%, p<0.001). SF3B1 and ASXL1 were frequently mutated in both TET2mut and TET2wt MDS (32% and 34%, 22% and 18%, respectively). In MDS with TET2mut compared to MDS with TET2wt the following genes were less frequently mutated: ATM (0.5% vs 3%, p=0.05), DNMT3A (9% vs 15%, p=0.02), ETV6 (0.5% vs 3%, p=0.03), IDH1 (0.5% vs 3%, p=0.02), IDH2 (1% vs 5%, p=0.002), TP53 (2% vs 7%, p=0.004), U2AF1 (4% vs 9%, p=0.04), while the following genes were more frequently mutated: CBL (6% vs 2%, p=0.01), EZH2 (8% vs 2%, p<0.001), SRSF2 (27% vs 12%, p<0.001), and ZRSR2 (15% vs 3%, p<0.001). Overall spliceosome genes were more frequently mutated in TET2mut than in TET2wt MDS (77% vs 56%, p<0.001).
In the total cohort A neither TET2mut nor TET2del had an impact on overall survival (OS). In TET2mut MDS and TET2wt MDS SF3B1mut were associated with favorable outcome, while TP53mut were associated with shorter OS in both subsets (table 1). However in TET2mut MDS mutations in RUNX1 (p<0.0001), CBL (p=0.001), and U2AF1 (p=0.03) were independently associated with shorter OS, while in TET2wt MDS mutations in KRAS (p=0.03), EZH2 (p=0.02), NRAS (p=0.02), SRSF2 (p=0.007), IDH2 (p=0.05), and ASXL1 (p=0.01) were independently associated with shorter OS.
In cohort B 40/77 (52%) MDS with TET2del also harbored a TET2mut. The 4q deletion encompassing the TET2 gene was < 10 MB in size and thus cytogenetically cryptic in 77% of cases with TET2mut, while the TET2 deletion was cryptic in only 24% of cases without TET2mut. A normal karyotype was present in 37 cases (48%), a complex karyotype in 29 (38%) and other abnormalities in 11 cases (14%). TET2mut were frequent in cases with a normal karyotype (68% vs aberrant karyotype: 32%, p<0.001) and were rare in cases with a complex karyotype (13%). Relating the mutation load of TET2mut to the proportion of cells with TET2del as determined by FISH revealed in 60% of cases that both TET2 alterations were present in the main clone, while in 23% of cases the TET2mut was present in a subclone only and in 17% the TET2del was observed in a subclone only. In the subset of patients with TET2del in a subclone only, 83% showed a normal karyotype and none a complex karyotype, while in the subset of cases with TET2mut in a subclone only, 43% showed a normal and 29% a complex karyotype. In the total cohort B the presence of a TET2mut in addition to the TET2del had no prognostic impact, while the presence of a complex karyotype was associated with shorter OS (RR: 8.0, p=0.004).
Conclusions: 1) TET2 deletions are rare in TET2 mutated MDS (3%). 2) TET2 mutations are frequent in MDS with TET2 deletion (52%). 3) TET2 mutations are highly correlated to a normal karyotype and are rare in complex karyotype. 3) Neither TET2 mutations nor TET2 deletions have a prognostic impact in MDS. 4) In TET2 mutated MDS mutations in RUNX1, TP53, CBL, and U2AF1 have the strongest negative independent impact on OS, which in TET2 wild-type MDS is the case for mutations in TP53, KRAS, EZH2, NRAS, SRSF2, IDH2 and ASXL1.
Table The relative risk of parameters significantly (p<0.05) associated with overall survival are depicted in TET2 mutated and TET2 wild-type MDS Table. The relative risk of parameters significantly (p<0.05) associated with overall survival are depicted in TET2 mutated and TET2 wild-type MDS

Disclosures
Haferlach: MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Stengel:MLL Munich Leukemia Laboratory: Employment. Meggendorfer:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Employment, Equity Ownership.