Mutation profile of the tall cell variant of papillary thyroid carcinoma: analysis of 5 cases using wide-panel next-generation sequencing

The study objective is to analyze the mutation profile of the tall cell variant (TCV) of papillary thyroid carcinoma (PTC).Materials and methods. The main inclusion criteria according to the WHO classification (2017) was PTC composed of at least 30 % of tall cells. Genetic examination was conducted using the FoundationOne CDx assay (USA) with median depth of coverage of >500x. This study included 5 patients (1 man and 4 women) with a mean age of 52.6 years (range: 48-56 years). The tumor size varied between 0.4 x 0.5 cm and 11.0 x 9.0 cm. All patients have undergone surgical treatment: hemithyroidectomy for patient No. 1 with a small tumor (pT1b); thyroidectomy for patient No. 2 (pT3b); extensive thyroidectomy with the removal of paratracheal tissue for patients No. 3, 4, and 5 (No. 3 - pT3bN0; No. 4 - pT3bN1b; No. 5 - pT3bN1b). Three out of the five patients also had adenomatous goiter. The mean follow-up time was 3.4 to 5.2 years.Results. Tumors in all patients were characterized by low mutational load (0 to 4 mutations per 1 million nucleotides (megabase)) and no microsatellite instability. All study participants were found to have p.V600E mutation in the BRAF gene; two patients had c.-124C>T mutation in the promoter region of the TERT gene. All patients carried mutations with unknown clinical significance: p.V562I in the EPHB1 gene (in 2 patients); mutations in the genes AR, CREBBP, EP300, ERCC4, FLT1, IKBKE, JAK2, MAF, MLL2, MST1R, MYC, MYCL1, NTRK2, TSC2 (each mutation registered in one patient). One individual with the largest tumor and the most aggressive disease was found to have amplifications of the BTG2, MAP3K1, SMAD2, and TBX3 genes.Conclusion. In 5 patients analyzed in this study, the mutation profile of TCV PTC was characterized by low mutational load, no microsatellite instability, and presence of p.V600E mutation in the BRAF gene in all cases. Some patients also had c.-124C>T mutation in the TERT gene and p.V562I mutation in the EPHB1 gene.