TERT promoter mutations in gliomas, genetic associations and clinico-pathological correlations

Abstract

Background: The role of telomerase reverse transcriptase (TERT) in gliomagenesis has been recently further strengthened by the frequent occurrence of TERT promoter mutations (TERTp-mut) in gliomas and evidence that the TERT SNP genetic rs2736100 influences glioma risk. TERTp-mut creates a binding site for Ets/TCF transcription factors, whereas the common rs2853669 polymorphism disrupts another Ets/TCF site on TERT promoter.

Methods: We sequenced for TERTp-mut in 807 glioma DNAs and in 235 blood DNAs and analysed TERT expression by RT-PCR in 151 samples. TERTp-mut status and TERTp polymorphism rs2853669 were correlated with histology, genomic profile, TERT mRNA expression, clinical outcome and rs2736100 genotype.

Results: TERTp-mut identified in 60.8% of gliomas (491 out of 807) was globally associated with poorer outcome (Hazard ratio (HR)=1.50). We defined, based on TERTp-mut and IDH mutation status, four prognostic groups: (1) TERTp-mut and IDH-mut associated with 1p19q codeletion, overall survival (OS)>17 years; (2) TERTp-wt and IDH-mut, associated with TP53 mutation, OS=97.5 months; (3) TERTp-wt and IDH-wt, with no specific association, OS=31.6 months; (4) TERTp-mut and IDH-wt, associated with EGFR amplification, OS=15.4 months. TERTp-mut was associated with higher TERT mRNA expression, whereas the rs2853669 variant was associated with lower TERT mRNA expression. The mutation of CIC (a repressor of ETV1-5 belonging to the Ets/TCF family) was also associated with TERT mRNA upregulation.

Conclusions: In addition to IDH mutation status, defining the TERTp-mut status of glial tumours should afford enhanced prognostic stratification of patients with glioma. We also show that TERTp-mut, rs2853669 variant and CIC mutation influence Tert expression. This effect could be mediated by Ets/TCF transcription factors.

Figure 1

Expression of TERT mRNA in gliomas. The Mann–Whitney test was used to compare the expression of the different groups. (A) Expression of TERT mRNA according to TERT promoter mutation status. TERTp mutation (C228T n=88 or C250T n=30) is associated with higher TERT mRNA expression compared with TERTp-wt group (n=35) (P⩽ 0.0001 in both cases). (B) Expression of TERT mRNA according to rs2853669 status. Variant allele carriers (n=70) present a lower TERT expression than TT homozygotes (n=66) (P=0.0053). (C) Expression of TERT mRNA according to TERTp and rs2853669 status. TERT mRNA expression is lower for the variant allele carriers (n=62) compared with TT (n=56) in TERTp-mut subgroup (P=0.0079). For TERTp-wt group, only seven CC+CT samples and eight TT samples were available. (D) Expression of TERT mRNA according to CIC mutation status. TERT mRNA expression is increased in CIC mutant tumours (n=18) compared with CIC wild type (n=11; P=0.043). (E) Impact of rs2853669 and CIC mutational status TERT expression. In the CIC-wt cohort, TERT expression was lower in CC+CT subgroup, as compared with TT subgroup (P=0.0159). For the variant allele carriers (CC+CT), expression of TERT was increased in the CIC mutant group (n=8), as compared with CIC wt (n=5) (P=0.0016). *P<0.05; **P<0.01; ***P<0.0001.

Figure 2

Prognostic impact of TERT promoter mutation status on overall survival and PFS, according to grade. Survivals were compared using the log-rank test (Mantel Cox). In grade II gliomas (n=206), TERTp mutation is associated with better survival (median >16 years vs 97.5 months; P=0.013). There is also a trend for better PFS (median 41.3 vs 33.3 months; P=0.068) (A) whereas in grade III (B; n=206) and grade IV gliomas (C; n=395), TERTp mutation is associated with poorer survival (median 29.4 vs 62.6 months P=0.013 and 13.8 vs 18.4 months P<0.0001) and PFS (median 15.1 vs 22.4 months P=0.006 and 8.3 vs 10.4 months P<0.0001).

Figure 3

Association of TERT promoter mutations with the major genetic alterations in gliomas (n=806). Each tumour is represented by a column. A yellow box indicates the presence of the genetic alteration, the absence in blue, and the cases not assessed are indicated in grey. The stratification has been done using four groups: IDH mut-TERTp mut, IDH mut-TERTp wt, IDH wt-TERTp wt and IDH wt TERTp mut. TERTp mutation is associated with two mutually exclusive alterations: 1p19q codeletion and EGFR amplification.

Figure 4

Prognostic stratification of gliomas according to IDH and TERT promoter mutation status (n=804). (A) Overall survival. (B) Progression-free survival. We identified four prognostic subgroups, (1) TERTp-mut and IDH-mut (OS> 17 years, PFS 46.9 months), (2) TERTp-wt and IDH-mut (OS=97.5 months, PFS 28.6 months), (3) TERTp-wt and IDH-wt, (OS=31.6 months, PFS14.1 months) and (4) TERTp-mut and IDH-wt (OS=15.0 months, PFS 8.5 months).

Figure 5

Prognostic stratification of gliomas according to IDH and TERT promoter mutation status (four subgroups) in grade II (n=205), grade III (n=206) and grade IV (n=394). Median survivals are indicated in months if not otherwise stated. TERTp mutation is associated with a poorer outcome in IDH-wt gliomas whatever the grade. TERTp mutation is associated with better outcome in IDH mut grades II and III (OS: >16 years vs 107.8 months in grade II P=0.004; >16 years vs 102.4 in grade III P=0.0005). In contrast, the survival of grade IV with TERTp mutation and IDH-mut is extremely poor compared with TERTp-wt (13.8 vs 29.1 months; P=0.022).

Figure 6

Prognostic stratification of gliomas according to grade in the four molecular subgroups (IDH mut TERTp mut n=122; IDH mut TERTp wt n=180; IDH wt TERTp wt n=114, IDH wt TERTp mut n=340). There is a dramatic difference of survival between grade IV (OS=13.8 months) and grades II+III (OS> 16 years) in the IDH-mut-TERT-mut group (P<0.0001). In contrast, the group 2 (IDH-mut-TERT-wt) is much more homogeneous through grades II–IV.