Low frequency of TERT promoter somatic mutation in 313 sporadic esophageal squamous cell carcinomas

Telomerase reverse transcriptase (TERT) gene encodes the catalytic subunit of telomerase; multiple independent variants at TERT locus are associated with telomere length and risk of malignant tumors.1 Recently point mutations in the promoter of TERT gene have been shown to occur in melanomas, gliomas and other tumors and the mutation increased telomerase expression.2-4 Esophageal cancer is the eighth most prevalent cancer in the world and squamous cell carcinoma (ESCC) is the major histological type in East Asian countries.5 Previous study has shown no mutations in TERT gene promoter in ESCCs, however, the small sample number (N = 22) yielded an inconclusive results.3 In present study, tissue sections were reviewed by two experienced pathologists, respectively, to ensure that tumor cell purity ≥50% and confirm histological type, and also each patient had clinical information in detail (Table 1). We extracted total DNA from ESCC tumor and adjacent normal tissue. Primers were used to amplify the sequence region containing the two previously described recurrent TERT promoter mutations (C228T and C250T, hg19).4 We analyzed the amplified fragment of tumor/normal pairs using Sanger sequencing with both directions to confirm the presence of the mutation. Finally, we evaluated TERT promoter mutations successfully in 313 ESCC samples and identified five somatic mutations (1.6%). C228T and C250T mutations occurred in four and one samples, respectively (Table 2). This result showed that the frequency of TERT promoter somatic mutation in ESCC was extremely low. The mutations did not correlate with any particular subtype such as age, sex, stage, lymph node metastasis and histological grade. We also analyzed our whole genome sequencing data from ten of stage I lung adenocarcinomas and revealed no somatic mutation, further analyses for large size samples are warranted. Previous studies have been shown that TERT promoter mutations of C228T and C250T create a new binding motif of GGAA (reverse complement of TTCC); and this motif is a binding site of E-twenty six (ETS) transcription factors. It has been proved that the members of the ETS transcription factor family associated with the development of different tissues as well as cancer progression.6 Comparison to the wild-type TERT promoter, reporter assays demonstrated that each mutation could increase the transcriptional activity and might augment telomerase expression.2, 3 In the amplified TERT promoter region, we also identified a common polymorphism rs2853669 with an A>G carrier variant frequency of 56.9% (178/313), similar with the 1000 Genomes database of CHB (Chinese population of Beijing) (61.8%, data available for 97 individuals, ENSEMBL). In contrast with C228T and C250T, rs2853669 was reported to disrupt an ETS binding site, which has been shown to affect telomerase activity and associate with cancer risk.7 We also identified two rare single nucleotide polymorphisms (SNPs) (rs35226131 and rs35161420) in the same case and two germline mutations (C216T and C433T) infrequently (Table 2). In summary, we showed for the first time that mutations in TERT promoter do occur in ESCC patients but at a very low frequency. This suggests that TERT promoter somatic mutations play a limited role in the ESCC development and progression. Yours sincerely, Yuda ZHAOYibo GAOZhaoli CHENXueda HUFang ZHOUJie HE