Spectrum of <i>TERT</i> promoter mutations and mechanisms of activation in thyroid cancer

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Reactivation of telomerase reverse transcriptase (<jats:italic>TERT</jats:italic>) is an important event in cancer. Two hotspot mutations in the <jats:italic>TERT</jats:italic> promoter region, c.‐124C > T (C228T) and c.‐146C > T (C250T), occur in various cancer types including thyroid cancer. They generate de novo binding sites for E‐twenty‐six (ETS) transcription factors causing increased <jats:italic>TERT</jats:italic> transcription. The aim of this study was to search for novel <jats:italic>TERT</jats:italic> promoter mutations and additional mechanisms of <jats:italic>TERT</jats:italic> activation in thyroid cancer.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>We studied 198 papillary thyroid carcinomas (PTCs), 34 follicular thyroid carcinomas (FTCs), 40 Hürthle cell carcinomas (HCCs), 14 poorly differentiated/anaplastic thyroid carcinomas (PDTC/ATC), and 15 medullary thyroid carcinomas (MTCs) for mutations in an −424 bp to +64 bp region of <jats:italic>TERT</jats:italic>. The luciferase reporter assay was used to functionally characterize the identified alterations. Copy number variations (CNVs) in the <jats:italic>TERT</jats:italic> region were analyzed using TaqMan copy number assay and validated with fluorescence in situ hybridization (FISH).</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>We detected the hotspot c.‐124C > T and c.‐146C > T mutations in 7% PTC, 18% FTC, 25% HCC, and 86% PDTC/ATC. One PTC carried a c.‐124C > A mutation. Furthermore, we identified two novel mutations resulting in the formation of de novo ETS‐binding motifs: c.‐332C > T in one MTC and c.‐104_‐83dup in one PTC. These genetic alterations, as well as other detected mutations, led to a significant increase in <jats:italic>TERT</jats:italic> promoter activity when assayed using luciferase reporter system. In addition, 5% of thyroid tumors were found to have ≥3 copies of <jats:italic>TERT</jats:italic>.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>This study confirms the increased prevalence of <jats:italic>TERT</jats:italic> promoter mutations and CNV in advanced thyroid cancers and describes novel functional alterations in the <jats:italic>TERT</jats:italic> gene promoter, including a point mutation and small duplication. These mutations, as well as <jats:italic>TERT</jats:italic> copy number alterations, may represent an additional mechanism of <jats:italic>TERT</jats:italic> activation in thyroid cancer.</jats:p></jats:sec>