TERT Promoter Mutation Spatial Heterogeneity in a Metastatic Follicular Thyroid Carcinoma: Implications for Clinical Work-Up

Abstract

Follicular thyroid carcinoma (FTC) is not routinely diagnosed by a preoperative fine needle aspiration biopsy (FNAB), and the final diagnosis relies on histopathological criteria visible upon microscopic examination of the excised tumor. Several markers have been proposed as helpful in the identification of follicular thyroid tumors with malignant potential and worse prognosis, of which the specific point mutations C250T and C228T in the Telomerase Reverse Transcriptase (TERT) promoter region seem to be particularly promising. We describe a patient presenting with a large pelvic mass, in which a core needle biopsy was consistent with follicular-patterned thyroid tissue positive for a Q61R NRAS mutation and the C228T TERT promoter mutation. Upon clinical investigation, a 60-mm lesion was detected in the right thyroid lobe. The ensuing FNAB was consistent with a follicular thyroid tumor, Bethesda IV, positive for the same NRAS mutation and both the C228T and C250T TERT promoter mutations. A total thyroidectomy was performed, and a widely invasive FTC was diagnosed. Tumor tissue samples from various parts of the primary lesion were investigated for TERT promoter mutations, displaying C228T in three samples and C250T in one. Interestingly, the C228T mutations showed a coupling to areas with high Ki-67 proliferation indexes. Our data indicate that TERT promoter mutations can exhibit spatial heterogeneity in FTCs, with implications for clinical management as well as providing insights into the molecular biology underlying the tumoral etiology.

Transcription Factor Profiling Identifies Spatially Heterogenous Mediators of Follicular Thyroid Cancer Invasion

“…Speculatively, one of the reasons for the persistent challenges in identifying markers of invasive FTC may be genetic or epigenetic intra-tumoral spatial heterogeneity [22]. In support of this theory, we identified significant differences between protein expressions of some transcription factors in the bulk of the tumor when compared with the invasive front by immunohistochemistry.…”

Effect of single‐nucleotide polymorphism in TERT promoter on follicular thyroid tumor development

“…The C228T mutation in FTCs appears to be much more frequent than predicted, and this location may be a hot spot for TERT mutations. Stenman et al described that TERT promoter mutations could exhibit spatial heterogeneity across FTCs. In the present study, the whole surface area of the tumor was used to analyze TERT promoter mutations, and this method could affect the lower peak of the gene analyzed.…”

Spatial Distribution Patterns of Clinically Relevant TERT Promoter Mutations in Follicular Thyroid Tumors of Uncertain Malignant Potential

“…However, we recently observed an FTC specimen exhibiting spatial heterogeneity, in which various regions of the primary tumor displayed either the C228T or the C250T mutation, whereas the synchronous bone metastasis was positive only for the C228T mutation. 26 Moreover, a potential coupling between the C228T mutation and higher Ki-67 proliferation indices was also observed. These findings suggest that TERT promoter mutations are heterogeneously distributed in subsets of thyroid cancer specimens, a hypothesis strengthened by recent, in-depth investigations of the clonality of these mutations.…”

“…Given previous studies suggesting a polyclonal distribution of these mutations in well-differentiated thyroid carcinomas, we speculated that the spatial heterogeneity might affect our interpretation and hence sought to determine the frequency of this phenomenon in a series of follicular thyroid tumors. 26,27 Moreover, we wanted to investigate the ddPCR technique as a complementary analysis to the conventional Sanger technique, as the former exhibit superior sensitivity when compared to the latter.…”

“…Interestingly, among our FT-UMPs, the two blocks exhibiting the C250T mutation by Sanger sequencing in an otherwise C228T mutation-positive tumor exhibited the lowest Ki-67 proliferation indexes among the three individual blocks from each case, which are in line with previous J o u r n a l P r e -p r o o f observations suggesting a coupling also to the specific TERT promoter mutation type. 26 As an alternative to screen blocks using Ki-67 and/or mitotic counts, one could also hypothesize that cutting of FFPE material from three different, random blocks with high tumor cell proportions into the same test tube would yield a similar improvement in sensitivity. However, as several of the mutations were subclonal and only detectable in <10% of the DNA molecules interrogated, the pathologist might risk diluting the mutation with wildtype areas, thereby failing to detect these mutations by conventional Sanger sequencing.…”