Telomere length and telomerase reverse transcriptase gene copy number in patients with papillary thyroid carcinoma

Role of telomere length in human carcinogenesis (Review)

Cancer is considered the most important clinical, social and economic issue regarding cause‑specific disability‑adjusted life years among all human pathologies. Exogenous, endogenous and individual factors, including genetic predisposition, participate in cancer triggering. Telomeres are specific DNA structures positioned at the end of chromosomes and consist of repetitive nucleotide sequences, which, together with shelterin proteins, facilitate the maintenance of chromosome stability, while protecting them from genomic erosion. Even though the connection between telomere status and carcinogenesis has been identified, the absence of a universal or even a cancer‑specific trend renders consent even more complex. It is indicative that both short and long telomere lengths have been associated with a high risk of cancer incidence. When evaluating risk associations between cancer and telomere length, a disparity appears to emerge. Even though shorter telomeres have been adopted as a marker of poorer health status and an older biological age, longer telomeres due to increased cell growth potential are associated with the acquirement of cancer‑initiating somatic mutations. Therefore, the present review aimed to comprehensively present the multifaceted pattern of telomere length and cancer incidence association.

Familial non medullary thyroid carcinoma: Beyond the syndromic forms

Familial non-medullary thyroid cancer is defined as the presence of non-medullary thyroid cancer in two or more first-degree relatives, in the absence of other predisposing factors. It represents up to 9% of differentiated thyroid cancers, and only a minority appears in well-known hereditary syndromes that associate thyroid cancer among many other clinical manifestations. However, in more than 95% of cases, thyroid cancer appears isolated, and its genetic causes have yet to be elucidated. We review here the current knowledge of the genetic basis of this pathology, as well as its clinical characteristics. Understanding the genetic mechanisms implied would help to comprehend the metabolic pathways involved, with the consequent potential therapeutic application. In addition, it would allow genetic counseling and to focus our efforts on patients at risk of developing this disorder.

Familial non-medullary thyroid cancer: a critical review

BACKGROUND

Familial non-medullary thyroid carcinoma (FNMTC), mainly of papillary histotype (FPTC), is defined by the presence of the disease in two or more first-degree relatives in the absence of other known familial syndromes. With the increasing incidence of PTC in the recent years, the familial form of the disease has also become more common than previously reported and constitutes nearly 10% of all thyroid cancers. Many aspects of FNMTC are debated, concerning both clinical and genetic aspects. Several studies reported that, in comparison with sporadic PTCs, FPTCs are more aggressive at disease presentation, while other authors reported no differences in the clinical behavior of sporadic and familial PTCs. For this reason, recent guidelines do not recommend screening of family members of patients with diagnosis of differentiated thyroid cancer (DTC). FNMTC is described as a polygenic disorder associated with multiple low- to moderate-penetrance susceptibility genes and incomplete penetrance. At the moment, the genetic factors contributing to the development of FNMTC remain poorly understood, though many putative genes have been proposed in the recent years.

PURPOSE

Based on current literature and our experience with FNMTC, in this review, we critically discussed the most relevant controversies, including its definition, the genetic background and some clinical aspects as screening and treatment.

Familial non medullary thyroid carcinoma: Beyond the syndromic forms

Familial non-medullary thyroid cancer is defined as the presence of non-medullary thyroid cancer in two or more first-degree relatives, in the absence of other predisposing factors. It represents up to 9% of differentiated thyroid cancers, and only a minority appears in well-known hereditary syndromes that associate thyroid cancer among many other clinical manifestations. However, in more than 95% of cases, thyroid cancer appears isolated, and its genetic causes have yet to be elucidated. We review here the current knowledge of the genetic basis of this pathology, as well as its clinical characteristics. Understanding the genetic mechanisms implied would help to comprehend the metabolic pathways involved, with the consequent potential therapeutic application. In addition, it would allow genetic counseling and to focus our efforts on patients at risk of developing this disorder.

Leukocyte Telomere Length and Risk of Papillary Thyroid Carcinoma

CONTEXT

Telomere length may contribute to predisposition to papillary thyroid cancer (PTC).

OBJECTIVE

To test this hypothesis, we examined the association between leukocyte telomere length and PTC risk.

DESIGN/SETTING

Case-control study in a Chinese Han population.

PARTICIPANTS/INTERVENTION

A total of 1200 PTC cases and 1201 age- and sex-matched healthy controls were included in the study. ORs and 95% CIs were calculated by logistic regression.

RESULTS

Short relative telomere length (RTL) was significantly associated with elevated risk of PTC (OR = 1.61, 95% CI = 1.35 to 1.92; P = 1.30 × 10-7). Interestingly, when individuals were categorized into four groups on the basis of quartile distribution of relative telomere length (RTL) in controls, we observed a reverse U-shaped association between telomere length and PTC risk. Compared with those in the first (the longest) quartile as the reference group, ORs (95% CIs) were 5.61 (4.04 to 7.78) (P = 6.10 × 10-25), 9.33 (6.78 to 12.83) (P = 6.99 × 10-43), and 1.23 (0.83 to 1.81) (P = 0.300) for individuals in the second, third, and fourth (the shortest) quartiles, respectively. This reverse U-shaped relationship was more apparent in younger individuals.

CONCLUSIONS

Our findings suggest that RTL is significantly associated with susceptibility to PTC. There is an obvious reverse U-shaped association between telomere length and PTC risk. Telomere length may be a potential pronouncing biomarker to identify individuals with a high risk of developing PTC.

TERT aberrancies: a screening tool for malignancy in follicular thyroid tumours

Telomerase reverse transcriptase (TERT) promoter mutations have been linked to adverse clinical parameters in thyroid cancer, but TERT-expressing tumours are not always mutated. Little is known regarding other TERT-related genetic aberrations. To delineate the role of TERT gene aberrancies in follicular thyroid tumours, 95 follicular carcinomas (FTCs), 43 follicular adenomas (FTAs) and 33 follicular tumours of uncertain malignant potential (FT-UMPs) were collected. The tumours were assayed for TERT expression, TERT promoter mutations, TERT promoter hypermethylation and TERT gene copy number (CN) alterations and the results were compared to clinical parameters. Cases with mutation, detectable mRNA expression, CN gain or hypermethylation were classified as TERT aberrant, and these aberrancies were regularly found in FTC and FT-UMP but uncommonly found in FTA. In total, 59% FTCs and 63% FT-UMPs exhibited one or more of these TERT gene aberrancies. Moreover, 24 out of 28 FTCs (86%) with TERT expression displayed an evident TERT gene aberration, and statistics showed an increased risk for relapse in FTCs with TERT expression, CN gain or hypermethylation. We conclude that TERT expression in follicular thyroid tumours is coupled to promoter mutations, CN gain and increased promoter methylation. The molecular similarities regarding TERT aberrations between the FTC and FT-UMP groups indicate that a significant subset of FT-UMP cases may display future recurrences. TERT aberrancies are thus promising as future additional markers for determining malignant potential of follicular thyroid tumours.

Identification of somatic TERT promoter mutations in familial nonmedullary thyroid carcinomas

OBJECTIVE

The genes causing familial nonmedullary thyroid carcinoma (FNMTC) identified to date are only involved in a small fraction of the families. Recently, somatic mutations in TERT promoter region and in EIF1AX gene were reported in thyroid tumours of undefined familial status. The aim of this study was to investigate the role of TERT and EIF1AX mutations in familial thyroid tumours.

DESIGN

The promoter region of TERT was sequenced in leucocyte DNA of the probands from 75 FNMTC families. In thyroid tumours from 54 familial cases, we assessed somatic TERT promoter, RAS and BRAF hotspot mutations, and the whole EIF1AX gene.

RESULTS

No potentially pathogenic germline variants were identified in TERT in the 75 FNMTC families' probands. In the 54 carcinomas, we identified five cases (9%) with hotspot somatic TERT promoter mutations. BRAF mutations were found in 41% of the tumours. All TERT-positive samples were also positive for BRAF p.Val600Glu, and this co-occurrence was found to be statistically significant (P=.008). RAS mutations were detected in four tumours wild-type for TERT (7%). Evaluation of tumour mutation data together with the patients' clinicopathological features revealed a significant correlation between TERT plus BRAF mutations and advanced tumour stage (T4) (P=.020). No mutations were identified in EIF1AX.

CONCLUSIONS

The results of this study suggest that TERT promoter and EIF1AX mutations are not frequently involved in FNMTC aetiology. However, we show for the first time that TERT alterations are associated with familial thyroid tumour progression. Our data also suggest that TERT mutations are more often found in concomitance with BRAF mutations in advanced stages of FNMTC.

Familial non-medullary thyroid cancer: unraveling the genetic maze

Familial non-medullary thyroid cancer (FNMTC) constitutes 3-9% of all thyroid cancers. Out of all FNMTC cases, only 5% in the syndromic form has well-studied driver germline mutations. These associated syndromes include Cowden syndrome, familial adenomatous polyposis, Gardner syndrome, Carney complex type 1, Werner syndrome and DICER1 syndrome. It is important for the clinician to recognize these phenotypes so that genetic counseling and testing can be initiated to enable surveillance for associated malignancies and genetic testing of family members. The susceptibility chromosomal loci and genes of 95% of FNMTC cases remain to be characterized. To date, 4 susceptibility genes have been identified (SRGAP1 gene (12q14), TITF-1/NKX2.1 gene (14q13), FOXE1 gene (9q22.33) and HABP2 gene (10q25.3)), out of which only the FOXE1 and the HABP2 genes have been validated by separate study groups. The causal genes located at the other 7 FNMTC-associated chromosomal loci (TCO (19q13.2), fPTC/ PRN (1q21), FTEN (8p23.1-p22), NMTC1 (2q21), MNG1 (14q32), 6q22, 8q24) have yet to be identified. Increasingly, gene regulatory mechanisms (miRNA and enhancer elements) are recognized to affect gene expression and FNMTC tumorigenesis. With newer sequencing technique, along with functional studies, there has been progress in the understanding of the genetic basis of FNMTC. In our review, we summarize the FNMTC studies to date and provide an update on the recently reported susceptibility genes including novel germline SEC23B variant in Cowden syndrome, SRGAP1 gene, FOXE1 gene and HABP2 genes in non-syndromic FNMTC.

Familial vs sporadic papillary thyroid carcinoma: a matched-case comparative study showing similar clinical/prognostic behaviour

OBJECTIVE

Familial non-medullary thyroid cancer has been proposed as an aggressive clinical entity. Our aim in this study is to investigate potential distinguishing features as well as the biological and clinical aggressiveness of familial vs sporadic papillary thyroid carcinoma (PTC). We assessed clinicopathological characteristics, outcome measures and DNA ploidy.

DESIGN

A matched-case comparative study.

METHODS

A series of patients with familial PTC (n=107) and two subgroups, one with three or more affected elements (n=32) and another including index cases only (n=61), were compared with patients with sporadic PTC (n=107), matched by age, gender, pTNM disease extension and approximate follow-up duration. Histological variant, extrathyroidal extension, vascular invasion, tumour multifocality and bilateral growth were evaluated. Ploidy pattern was analysed in available samples by DNA flow cytometry. The probabilities of disease-free survival (DFS) and overall survival (OS) were estimated according to the Kaplan-Meier (K-M) method.

RESULTS

No patient with familial PTC died of disease during follow-up (median, 72 months), contrarily to five patients (4.7%) (P=0.06) with sporadic PTC (median, 90 months). There was a significantly higher tumour multifocality in familial PTC (index cases subgroup) vs sporadic PTC (P=0.035), and a trend, in the familial PTC cohort with three or more affected elements, to show extrathyroidal extension (P=0.054) more frequently. No difference was observed in DNA ploidy status. The K-M analyses showed no significant differences between both entities in relation to DFS or OS.

CONCLUSION

Apart from multifocality, familial PTC appears to have similar clinical/prognostic behaviour when compared with sporadic forms of the disease.

Controversies in familial thyroid cancer 2014

Thyroid cancer is the sixth most common cancer in women, and the majority of patients with thyroid cancer has sporadic disease. However, about 25% of patients with medullary thyroid cancer and 5% with papillary thyroid cancer have familial tumors. Currently, there are numerous controversies regarding the mode of inheritance, tumor behavior, extent of surgical resection for optimal results, coexisting thyroid pathology, risk of other cancers, and extent of postoperative treatment of patients with familial thyroid cancer. This review aimed to give insight to surgeons on this interesting topic.

Familial nonmedullary thyroid carcinoma

BACKGROUND

Nonmedullary thyroid cancers (NMTC) originate from the follicular cells of the thyroid gland and account for over 90% of all thyroid cancers. About 3-10% of the NMTCs are of familial origin, and familial NMTC (FNMTC) is defined as two or more affected first-degree relatives with NMTC in the absence of other known familial syndromes.

SUMMARY

The genes involved in the pathogenesis of FNMTC are yet to be elucidated, although some recent studies identified several predisposition loci with a high degree of genetic heterogeneity. To date, several studies have evaluated the aggressive tumor characteristics associated with FNMTC with conflicting results. Several studies demonstrated that patients with FNMTC have increased rates of multifocal disease, extrathyroidal invasion, and involved lymph nodes compared with sporadic disease. It has been hypothesized that this increased aggressiveness translates into higher recurrence rates and decreased survival of patients with FNMTC.

CONCLUSION

This review highlights clinical aspects and management dilemmas as well as controversial issues in FNMTC. Management recommendations are deduced.

Telomere length is shorter in affected members of families with familial nonmedullary thyroid cancer

BACKGROUND

The theory that short telomere length and genetic defects in maintaining telomere length are associated with familial nonmedullary thyroid cancer (FNMTC) is controversial. Thus, the aim of this study was to determine whether telomere length and genes involved in maintaining telomere length are altered in FNMTC.

METHODS

Blood samples were collected from 44 members (13 affected and 31 unaffected) of six families with FNMTC and from 60 controls. Quantitative polymerase chain reaction (Q-PCR) and reverse transcription PCR were performed to analyze relative telomere length (RTL), gene copy number, and mRNA expression of telomerase reverse transcriptase (hTERT), telomere repeat binding factor 1 (TRF1), telomere repeat binding factor 2 (TRF2), repressor activator protein 1 (RAP1), TRF1 interacting nuclear factor 2 (TIN2), tripeptidyl peptidase 1 (TPP1), and protection of telomere 1 (POT1).

RESULTS

Affected members had shorter RTL, as compared with unaffected members (0.98 vs. 1.23, p<0.01). There was no significant difference in hTERT, TRF1, TRF2, RAP1, TIN2, TPP1, and POT1 gene copy number or mRNA expression between affected and unaffected members.

CONCLUSIONS

RTL is shorter in affected members with FNMTC but is not associated with altered copy number or expression in hTERT, TRF1, TRF2, RAP1, TIN2, TPP1, and POT1. The small differences in RTL preclude the utility of RTL as a marker for FNMTC in at-risk individuals.