Fusion Oncogenes Are the Main Genetic Events Found in Sporadic Papillary Thyroid Carcinomas from Children

Historical context, process, and development trends of pediatric thyroid cancer research: a bibliometric analysis

Objective

At present, the structure of knowledge in the field of childhood thyroid cancer is not clear enough, and scholars lack a sufficient understanding of the developing trends in this field, which has led to a shortage of forward-looking outputs. The purpose of this research is to help scholars construct a complete knowledge framework and identify current challenges, opportunities, and development trends.

Methods

We searched the literature in the Web of Science Core Collection database on August 7, 2023 and extracted key information from the top 100 most cited articles, such as the countries, institutions, authors, themes, and keywords. We used bibliometric tools such as bibliometrix, VOSviewer, and CiteSpace for a visualization analysis and Excel for statistical descriptions.

Results

The top 100 most cited articles fluctuated over time, and the research was concentrated in European countries, the United States, and Japan, among which scientific research institutions and scholars from the United States made outstanding contributions. Keyword analysis revealed that research has shifted from simple treatment methods for pediatric thyroid cancer (total thyroidectomy) and inducing factors (the Chernobyl power station accident) to the clinical applications of genetic mutations (such as the BRAF and RET genes) and larger-scale genetic changes (mutation studies of the DICER1 gene). The thematic strategy analysis showed an increasing trend towards the popularity of fusion oncogenes, while the popularity of research on traditional treatments and diagnostics has gradually declined.

Conclusion

Extensive research has been conducted on the basic problems of pediatric thyroid cancer, and there has been significant outputs in the follow-up and cohort analysis of conventional diagnostic and treatment methods. However, these methods still have certain limitations. Therefore, scholars should focus on exploring fusion genes, the clinical applications of molecular targets, and novel treatment methods. This study provides a strong reference for scholars in this field.

Genetic alterations landscape in paediatric thyroid tumours and/or differentiated thyroid cancer: Systematic review

Differentiated thyroid cancer (DTC) is a rare disease in the paediatric population (≤ 18 years old. at diagnosis). Increasing incidence is reflected by increases in incidence for papillary thyroid carcinoma (PTC) subtypes. Compared to those of adults, despite aggressive presentation, paediatric DTC has an excellent prognosis. As for adult DTC, European and American guidelines recommend individualised management, based on the differences in clinical presentation and genetic findings. Therefore, we conducted a systematic review to identify the epidemiological landscape of all genetic alterations so far investigated in paediatric populations at diagnosis affected by thyroid tumours and/or DTC that have improved and/or informed preventive and/or curative diagnostic and prognostic clinical conduct globally. Fusions involving the gene RET followed by NTRK, ALK and BRAF, were the most prevalent rearrangements found in paediatric PTC. BRAF V600E was found at lower prevalence in paediatric (especially ≤ 10 years old) than in adults PTC. We identified TERT and RAS mutations at very low prevalence in most countries. DICER1 SNVs, while found at higher prevalence in few countries, they were found in both benign and DTC. Although the precise role of DICER1 is not fully understood, it has been hypothesised that additional genetic alterations, similar to that observed for RAS gene, might be required for the malignant transformation of these nodules. Regarding aggressiveness, fusion oncogenes may have a higher growth impact compared with BRAF V600E. We reported the shortcomings of the systematized research and outlined three key recommendations for global authors to improve and inform precision health approaches, glocally.

Molecular testing for thyroid nodules: Where are we now?

Approximately 25% of the fine needle aspiration samples (FNAB) of thyroid nodules are classified as "indeterminate samples", that means, Bethesda III and IV categories. Until the last decade, most of these cases underwent diagnostic surgery, although only a minority (13-34%) confirmed malignancy postoperatively. In view of this, with the objective of improving the preoperative diagnosis in these cases, the molecular tests emerged, which are validated from the diagnostic point of view, presenting good performance, with good diagnostic accuracy, being able to avoid diagnostic surgeries. With the advancement of knowledge of the role of each of the mutations and gene rearrangements in thyroid oncogenesis, molecular markers have left to play only a diagnostic role and have been gaining more and more space both in defining the prognostic role of the tumor, as well as in the indication of target therapy. Thus, the objective of this review is to show how to use the tool of molecular tests, now commercially available in the world, in the management of indeterminate cytological nodules, assessing the pre-test malignancy risk of the nodule, through clinical, ultrasonographic and cytological characteristics, and decide on the benefit of molecular testing for each patient. In addition, to discuss its new and promising prognostic and therapeutic role in thyroid cancer.

Thyroid Nodules and Follicular Cell-Derived Thyroid Carcinomas in Children

Although pediatric thyroid tumors have many similarities to those occurring in adults, significant differences are also recognized. For example, although thyroid nodules in children are much less common than in adults, a higher percentage is malignant. Moreover, while pediatric papillary thyroid carcinoma (PTC) is associated with more advanced disease, death due to disease in children and adolescents is very rare, even when distant metastases are present. Some subtypes of thyroid carcinoma, like diffuse sclerosing variant, are especially common in children and adolescents. Moreover, certain histologic findings, such as a tall cell morphology or increased mitotic activity, may not carry the same prognostic significance in children as in adults. Recent studies exploring the molecular underpinnings of pediatric thyroid carcinoma indicate that while driver alterations of thyroid tumorigenesis in children and adults are essentially the same, they occur at very different frequencies, with translocation-associated tumors (most commonly harboring RET and NTRK fusions) comprising a sizable and distinct group of pediatric PTC. DICER1 mutations, an infrequent mutation in adult thyroid tumors, are relatively frequent in pediatric encapsulated follicular-patterned thyroid tumors (with or without invasion or nuclear features of PTC). Additionally, tumor predisposition syndromes (most notably DICER1 syndrome and PTEN hamartoma tumor syndromes such as Cowden syndrome) should be considered in children with thyroid tumors, especially follicular-patterned thyroid tumors and poorly differentiated thyroid carcinoma. This review will explore the current state of knowledge of thyroid nodules and carcinomas in children and adolescents.

The Prognostic Significance of BRAF Gene Analysis in Children and Adolescents with Papillary Thyroid Carcinoma: A Systematic Review and Meta-Analysis

Thyroid cancer represents the prominent endocrine cancer in children. Papillary thyroid cancer (PTC) constitutes its most frequent (>90%) pediatric histological type. Mutations energizing the mitogen-activated-protein kinase (MAPK) pathway are definitely related to PTC. Its most common genetic alteration is in proto-oncogene B-Raf (BRAF). Mutated BRAF is proposed as a prognostic tool in adult PTC. We conducted a systematic review and meta-analysis evaluating the association of mutated BRAF gene and prognostic clinicopathological characteristics of PTC in children/adolescents. Systematic search for relevant studies included PubMed, MEDLINE, Scopus, clinicaltrials.gov and Cochrane Library. Pooled estimates of odds ratios for categorical data and mean difference for continuous outcomes were calculated using random/fixed-effect meta-analytic models. BRAFV600E mutation presents a pooled pediatric/adolescent prevalence of 33.12%. Distant metastasis is significantly associated with mutated BRAF gene (OR = 0.32, 95% CI = 0.16-0.61, p = 0.001). Tumor size (MD = -0.24, 95% CI = -0.62-0.135, p = 0.21), multifocality (OR = 1.13, 95% CI = 0.65-2.34, p = 0.74), vascular invasion (OR = 1.17, 95% CI = 0.67-2.05, p = 0.57), lymph node metastasis (OR = 0.92, 95% CI = 0.63-1.33, p = 0.66), extra-thyroid extension (OR = 0.78, 95% CI = 0.53-1.13, p = 0.19) and tumor recurrence (OR = 1.66, 95% CI = 0.68-4.21, p = 0.376) presented no association or risk with BRAF mutation among pediatric/adolescent PTC. Mutated BRAF gene in children and adolescents is less common than in adults. Mutation in BRAF relates significantly to distant metastasis among children/adolescents with PTC.

Radioactive Iodine-Refractory Pulmonary Metastases of Papillary Thyroid Cancer in Children, Adolescents, and Young Adults

CONTEXT

Few studies have explored radioactive iodine-refractory (RAIR) disease in children, adolescents, and young adults with papillary thyroid cancer (CAYA-PTC).

OBJECTIVE

This study systematically investigated the clinicopathologic characteristics and prognosis of CAYA-PTC with RAIR disease.

METHODS

Sixty-five patients with PTC aged ≤20 years were enrolled in this study, and all patients were confirmed to have pulmonary metastases. Clinicopathologic profiles were compared between the radioactive iodine-avid (RAIA) and RAIR groups. Univariate and multivariate regression analyses were performed to identify risk factors for RAIR status and progressive disease (PD). Gene alterations were detected in 17 patients.

RESULTS

Overall, 20 patients were included in the RAIR group, accounting for 30.8% (20/65) of all patients. No significant difference in pathologic characteristics was observed between patients aged <15 years and patients aged 15-20 years, but younger patients were more likely to develop RAIR disease (hazard ratio [HR] 3.500, 95% CI 1.134-10.803, P = .023). RET fusions were the most common genetic alterations in CAYA-PTC, but an association with RAIR disease was not detected (P = .210). RAIR disease (HR 10.008, 95% CI 2.427-41.268, P = .001) was identified as an independent predictor of PD. The Kaplan-Meier curve revealed a lower progression-free survival (PFS) and disease-specific survival (DSS) rate in the RAIR group than in the RAIA group (P < .001 and P = .039). Likewise, RAIR disease was a risk factor for unfavorable PFS in patients aged <15 years (P < .001).

CONCLUSION

RAIR disease occurs in one-third of CAYA-PTC with pulmonary metastases. Younger patients (aged < 15 years) are more susceptible to RAIR status, which leads to unfavorable PFS and DSS.

Molecular Landscape of Pediatric Thyroid Cancer: A Review

Thyroid carcinomas (TC) are rare in the pediatric population; however, they constitute the most common endocrine malignancy. Despite some similarities with adult carcinomas, they have distinct clinical behavior and responses to therapy due to their unique pathology and molecular characteristics. The age cut-off used for defining the pediatric age group has been variable across different studies, and the universally accepted recommendations influence accurate interpretation of the available data. Moreover, factors such as radiation exposure and germline mutations have greater impact in children than in adults. Papillary TC is the most common and the most evaluated pediatric TC. Others, including follicular, poorly differentiated and medullary carcinomas, are rarer and have limited available literature. Most studies are from the West. Asian studies are primarily from Japan, with few from China, India, Saudi Arabia and Republic of Korea. This review provides a comprehensive account of the well-established and novel biomarkers in the field, including point mutations, fusions, miRNA, and thyroid differentiation genes. Familial and syndromic associations are also discussed. Current management guidelines for pediatric patients are largely derived from those for adults. An awareness of the molecular landscape is essential to acknowledge the uniqueness of these tumors and establish specific diagnostic and therapeutic guidelines.

Case report: Dramatic response to pralsetinib in an elderly patient with advanced RET-fusion positive papillary thyroid carcinoma

We are recently faced with a progressive evolution of the therapeutic paradigm for radioiodine refractory differentiated thyroid cancer (RAI-R DTC), since the advent of tissue agnostic inhibitors. Thus, tumor genotype assessment is always more relevant and is playing a crucial role into clinical practice. We report the case of an elderly patient with advanced papillary thyroid carcinoma (PTC) harboring RET-CCDC6 fusion with four co-occurring mutations involving PI3KCA, TP53, and hTERT mutations, treated with pralsetinib under a compassionate use program. Despite the high histological grade and the coexistence of aggressive RET co-mutations, an impressive metabolic and structural tumor response has been obtained, together with a patient's prolonged clinical benefit. A timely comprehensive molecular testing of those cases wild-type for the common thyroid carcinoma BRAF V600E-like and RAS-like driver mutations may uncover actionable gene rearrangements that can be targeted by highly selective inhibitors with great potential benefit for the patients.

Limited Accuracy of Pan-Trk Immunohistochemistry Screening for NTRK Rearrangements in Follicular-Derived Thyroid Carcinoma

Patients with advanced thyroid cancer harboring NTRK rearrangements can be treated with highly effective selective inhibitors. Immunohistochemistry (IHC) analysis, to detect Trk protein expression, represents an appealing screening strategy for NTRK rearrangements, but its efficacy has been poorly explored in thyroid cancer. The aim of this study is to investigate the diagnostic utility of Trk IHC in the identification of NTRK rearrangements. A series of 26 follicular-derived thyroid tumors, positive for NTRK rearrangements, and 28 NTRK fusion-negative controls were retrospectively analyzed by IHC using the pan-Trk monoclonal antibody (clone EPR17341) on the Ventana system. Area under the curve (AUC), sensitivity and specificity were calculated by ROC analysis. Trk expression was detected in 25 samples, including 22 out of the 26 NTRK-rearranged (84.6%) and three out of 28 NTRK-negative samples (10.7%). Four out of twenty-six NTRK-rearranged thyroid tumors were negative for Trk expression (15.4%), all carrying the ETV6/NTRK3 fusion. The AUC, sensitivity and specificity were 0.87, 0.85 and 0.89, respectively. A screening based on IHC analysis showed limited sensitivity and specificity in the identification of NTRK-rearranged tumors. Since falsely negative results could preclude the administration of effective targeted drugs, alternative detection strategies should be considered for thyroid cancer.

Genomic landscape of sporadic pediatric differentiated thyroid cancers: a systematic review and meta-analysis

OBJECTIVES

Differentiated thyroid cancers (DTCs) in the paediatric population differ from that of their adult counterparts in terms of clinicopathological characteristics and treatment outcomes. This systematic review and meta-analysis was conducted to comprehensively evaluate the prevalence of various genetic alterations underlying the pathogenesis of sporadic paediatric DTCs.

METHODS

This study followed the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) guidelines. Systematic searches were made on the PubMed and Embase databases using relevant keywords, and articles published until October 15, 2021 were selected. Data on the prevalence of various genetic alterations were extracted from the individual articles. Random-effects model was employed for meta-analysis to generate pooled estimates and their 95% confidence intervals (95% CIs).

RESULTS

Thirty-three articles comprising 1,380 paediatric patients were included. RET rearrangement (pooled prevalence: 24.4%, 95% CI: 19.1-30.1) was observed to be the most common genetic alteration in sporadic paediatric DTCs, closely followed by BRAF point mutation (pooled prevalence: 21.2%, 95% CI: 17.2-25.5). Other common alterations included: NTRK rearrangement (pooled prevalence: 13.5%, 95% CI: 9.5-17.9) and DICER1 mutation (pooled prevalence: 12.5%, 95% CI: 3.6-25.7). RAS and TERT mutations were observed to be relatively uncommon (pooled prevalence: 5.7%, 95% CI: 2.9-9.3, and 2.2%, 95% CI: 0.4-5.5, respectively). There was no evidence of publication bias.

CONCLUSIONS

Fusion oncogenes are noted to be the major oncogenic drivers in sporadic paediatric DTCs and underlie their unique behaviour. However, despite the relatively lower frequency of BRAF point mutation compared to adults, it remains a major player in childhood DTCs.

Mutational analysis using next generation sequencing in pediatric thyroid cancer reveals BRAF and fusion oncogenes are common

BACKGROUND

We previously described mutation rates of BRAF^V600E, RAS, RET-PTC and PAX8-PPARγ in pediatric subjects with well-differentiated thyroid cancer (WDTC). We expanded the cohort adding next-generation sequencing (NGS) and assessed genotype-phenotype correlations.

METHODS

Single-center retrospective cohort examining thyroidectomy tissue blocks from consecutive pediatric WDTC patients between 2001 and 2015. Tissues were analyzed at Quest Diagnostics for BRAF, RAS mutations, RET-PTC and PAX8-PPARγ, and additional fusions, using standalone and NGS tests. WDTC included papillary (PTC), follicular (FTC) and follicular-variant PTC (FVPTC).

RESULTS

We genotyped 46 samples (36 females). Mean age at diagnosis was 14.7 years and the cohort comprised of mostly Hispanic (60.9%) and Caucasian (26.1%) patients. Mean follow-up was 3.5 years. Genetic alterations (GA) were noted in 69.6%, with BRAF^V600E (n = 11), and RET-PTC (n = 8) detected only in PTC. GA were detected in 2/7 FTC (1 PAX8-PPARγ, 1 NRAS) and 6/10 FVPTC (3 PAX8-PPARγ, 1 STRN-ALK, 1 BRAF^K601E, 1 NRAS). Patients with BRAF^V600E were predominantly Hispanic (81.8%) and >15 years (81.8%), whereas 87.5% RET-PTC and 50% other-fusions occurred in patients ≤15 years (p = 0.044). Of the 29 PTC patients, 82.8% had GA: BRAF^V600E (37.9%), RET-PTC (27.6%), 17.2% other fusion-oncogenes (2 -ALK, 3 -NTRK). Non-RET fusions had the highest vascular invasion (100%, p = 0.042 vs RET-PTC) and frequent lymphatic invasion (80%). GA were most common in PTC with cervical metastasis.

CONCLUSIONS

BRAF^V600E was the most common single mutation, especially in older and Hispanic adolescents. All fusions combined are more common than BRAF^V600E. NGS reveals a genetic basis in most pediatric WDTC, which may have implications for the role of molecular testing and systemic therapy.

Prognostic value of lymph node ratio in children and adolescents with papillary thyroid cancer

OBJECTIVE

Neck lymph node (LN) metastasis is a common feature of paediatric papillary thyroid cancer, and LN ratio (LNR) is defined as the ratio of the number of positive LNs excised to the total number of removed. Unlike in adults, few data are available regarding the clinical implication of LNR in the paediatric population. Our purpose was to investigate the association of LNR with clinical outcomes in paediatric papillary thyroid cancer.

DESIGN & METHODS

The study retrospectively reviewed 136 consecutive children and adolescents with papillary thyroid cancer and LN involvement but no initial distant metastasis. Initial treatment, included in all patients a total thyroidectomy with central and/or lateral neck dissection followed by radioactive iodine ablation. Within the neck dissections, total number of LNs removed, total positive LNs and LN ratios were determined. The effect of clinicopathologic characteristics and intraoperative findings on persistent and recurrent diseases were analysed by univariate and multivariate analyses.

RESULTS

Median number of positive LNs was 9, and median LNR was 0.4. During a median follow-up of 49 months (range, 12.0-139 months), persistent disease occurred in 43 (31.6%) patients. The multivariable analysis showed that age and LNR were the independent factors predictive of persistent disease. Patients with a LNR >0.34 exhibited a threefold higher risk of persistent disease after initial therapy than the counterparts (P = .02).

CONCLUSION

Our findings suggest that LNR was an independent determinant predictive of persistent disease after initial therapy in children and adolescents with papillary thyroid cancer.

Diverse Oncogenic Fusions and Distinct Gene Expression Patterns Define the Genomic Landscape of Pediatric Papillary Thyroid Carcinoma

Pediatric papillary thyroid carcinoma (PPTC) is clinically distinct from adult-onset disease. Although there are higher rates of metastasis and recurrence in PPTC, prognosis remains highly favorable. Molecular characterization of PPTC has been lacking. Historically, only 40% to 50% of childhood papillary thyroid carcinoma (PTC) were known to be driven by genomic variants common to adult PTC; oncogenic drivers in the remainder were unknown. This contrasts with approximately 90% of adult PTC driven by a discrete number of variants. In this study, 52 PPTCs underwent candidate gene testing, followed in a subset by whole-exome and transcriptome sequencing. Within these samples, candidate gene testing identified variants in 31 (60%) tumors, while exome and transcriptome sequencing identified oncogenic variants in 19 of 21 (90%) remaining tumors. The latter were enriched for oncogenic fusions, with 11 nonrecurrent fusion transcripts, including two previously undescribed fusions, STRN-RET and TG-PBF. Most fusions were associated with 3' receptor tyrosine kinase (RTK) moieties: RET, MET, ALK, and NTRK3. For advanced (distally metastatic) tumors, a driver variant was described in 91%. Gene expression analysis defined three clusters that demonstrated distinct expression of genes involved in thyroid differentiation and MAPK signaling. Among RET-CCDC6-driven tumors, gene expression in pediatric tumors was distinguishable from that in adults. Collectively, these results show that the genomic landscape of pediatric PTC is different from adult PTC. Moreover, they identify genomic drivers in 98% of PPTCs, predominantly oncogenic fusion transcripts involving RTKs, with a pronounced impact on gene expression. Notably, most advanced tumors were driven by a variant for which targeted systemic therapy exists. SIGNIFICANCE: This study highlights important distinctions between the genomes and transcriptomes of pediatric and adult papillary thyroid carcinoma, with implications for understanding the biology, diagnosis, and treatment of advanced disease in children.

Kinase fusion-related thyroid carcinomas: distinct pathologic entities with evolving diagnostic implications

Activating genomic alterations in protein kinases represent a major driving force in thyroid carcinogenesis. Recently, oncogenic kinase fusions have been a central subject of pharmaceutical development, with a rapidly growing number of inhibitors validated for treating molecularly matched malignancies. Thyroid carcinomas harbor actionable kinase fusions in 10-15% of cases, occupying an increasingly recognized subpopulation of thyroid carcinomas with enhanced attention to molecular profiling. With advances in kinase-based cancer therapy, several challenges have emerged for pathologists. To interrogate an expanding list of targetable genes, the diagnostic paradigm has shifted from conventional single-gene methods toward high-throughput nucleic acid sequencing. Considering the relatively low incidence of most kinase fusions, a selective approach for molecular testing that utilizes histologic and immunohistochemical findings in triaging cases becomes essential for laboratory resource management. Moreover, kinase inhibitor resistance inevitably evolves, requiring a multimodal approach to optimal therapy, despite targeted therapies showing an enhanced, durable response. In this review, we assess the current clinicopathologic understanding and ongoing investigational topics in kinase fusion-related thyroid carcinomas.

Development of metastatic poorly differentiated thyroid cancer from a sub-centimeter papillary thyroid carcinoma in a young patient with a germline MET mutation - association or random chance?

Background

Thyroid cancer dedifferentiation is an unusual observation among young patients and is poorly understood, although a recent correlation to DICER1 gene mutations has been proposed.

Case presentation

A 28-year old patient presented with a sub-centimeter cytology-verified primary papillary thyroid carcinoma (PTC) and a synchronous lateral lymph node metastasis. Following surgery, histopathology confirmed a 9 mm oxyphilic PTC and a synchronous metastasis of poorly differentiated thyroid carcinoma (PDTC). Extensive molecular examinations of both lesions revealed wildtype DICER1 sequences, but identified a somatic ETV6-NTRK3 gene fusion and a MET germline variant (c.1076G > A, p.Arg359Gln). MET is an established oncogene known to be overexpressed in thyroid cancer, and this specific alteration was not reported as a single nucleotide polymorphism (SNP), suggestive of a mutation. Both the primary PTC and the metastatic PDTC displayed strong MET immunoreactivity. A validation cohort of 50 PTCs from young patients were analyzed using quantitative real-time PCR, revealing significantly higher MET gene expression in tumors than normal thyroid controls, a finding which was particularly pronounced in BRAF V600E mutated cases. No additional tumors apart from the index case harbored the p.Arg359Gln MET mutation. Transfecting PTC cell lines MDA-T32 and MDA-T41 with a p.Arg359Gln MET plasmid construct revealed no obvious effects on cellular migratory or invasive properties, whereas overexpression of wildtype MET stimulated invasion.

Conclusions

The question of whether the observed MET mutation in any way influenced the dedifferentiation of a primary PTC into a PDTC metastasis remains to be established. Moreover, our data corroborate earlier studies, indicating that MET is aberrantly expressed in PTC and may influence the invasive behavior of these tumors.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13044-021-00110-4.

NTRK- and RET-fusion-directed therapy in pediatric thyroid cancer yields a tumor response and radioiodine uptake

BACKGROUND

Molecular characterization in pediatric papillary thyroid cancer (PTC), distinct from adult PTC, is important for developing molecular targeted therapies for progressive 131I-refractory PTC.

METHODS

PTC samples from 106 pediatric patients (age: 4.3-19.8 years; 21 boys) who attended Seoul National University Hospital (January 1983-March 2020) were available for genomic profiling. Previous transcriptome data from 125 adult PTCs were used for comparison.

RESULTS

Genetic drivers were found in 80 tumors; 31 with fusion oncogenes (RET in 21, ALK in 6, and NTRK1/3 in 4), 47 with point mutations (BRAFV600E in 41, TERTC228T in 2, and DICER1 variants in 5), and 2 with amplifications. Fusion-oncogene PTCs, predominantly detected in younger patients, presented with a more advanced stage and showed more recurrent or persistent disease than BRAFV600E PTCs, which were detected mostly in adolescents. Pediatric fusion PTCs (in those aged < 10 years) showed lower expression of thyroid differentiation genes, including SLC5A5, than adult fusion PTCs. Two girls with progressive 131I-refractory lung metastases harboring a TPR-NTRK1 or CCDC6-RET fusion received fusion-targeted therapy; larotrectinib and selpercatinib decreased the tumor extent and restored radioiodine uptake. The girl with the CCDC6-RET fusion received 131I therapy combined with selpercatinib, leading to a tumor response. In vitro 125I uptake and 131I clonogenic assays showed that larotrectinib inhibited growth and restored radioiodine avidity.

CONCLUSIONS

In pediatric fusion-oncogene PTC cases with 131I-refractory advanced disease, selective fusion-directed therapy may restore radioiodine avidity and lead to a dramatic tumor response, underscoring the importance of molecular testing in pediatric PTC patients.

FUNDING

The Ministry of Science, ICT & Future Planning (grant number NRF-2016R1A2B4012417 91 and 2019R1A2C2084332), the Ministry of Health & Welfare, Republic of Korea (grant number 92 H14C1277), the Ministry of Education (grant number 2020R1A6A1A03047972), and the Seoul 93 National University Hospital Research Fund (grant number 04-2015-0830).

Major Oncogenic Drivers and Their Clinicopathological Correlations in Sporadic Childhood Papillary Thyroid Carcinoma in Belarus

Childhood papillary thyroid carcinoma (PTC) diagnosed after the Chernobyl accident in Belarus displayed a high frequency of gene rearrangements and low frequency of point mutations. Since 2001, only sporadic thyroid cancer occurs in children aged up to 14 years but its molecular characteristics have not been reported. Here, we determine the major oncogenic events in PTC from non-exposed Belarusian children and assess their clinicopathological correlations. Among the 34 tumors, 23 (67.6%) harbored one of the mutually exclusive oncogenes: 5 (14.7%) BRAFV600E, 4 (11.8%) RET/PTC1, 6 (17.6%) RET/PTC3, 2 (5.9%) rare fusion genes, and 6 (17.6%) ETV6ex4/NTRK3. No mutations in codons 12, 13, and 61 of K-, N- and H-RAS, BRAFK601E, or ETV6ex5/NTRK3 or AKAP9/BRAF were detected. Fusion genes were significantly more frequent than BRAFV600E (p = 0.002). Clinicopathologically, RET/PTC3 was associated with solid growth pattern and higher tumor aggressiveness, BRAFV600E and RET/PTC1 with classic papillary morphology and mild clinical phenotype, and ETV6ex4/NTRK3 with follicular-patterned PTC and reduced aggressiveness. The spectrum of driver mutations in sporadic childhood PTC in Belarus largely parallels that in Chernobyl PTC, yet the frequencies of some oncogenes may likely differ from those in the early-onset Chernobyl PTC; clinicopathological features correlate with the oncogene type.

Molecular Alterations in Relation to Histopathological Characteristics in a Large Series of Pediatric Papillary Thyroid Carcinoma from a Single Institution

Papillary thyroid carcinoma (PTC) presents distinct clinico-pathological and molecular differences in children compared with adult patients. Whether the presence of rearrangements or point mutations is associated with aggressive PTC clinical presentation is still controversial. In this study, PTCs diagnosed in patients aged less than 18 years were retrospectively searched from the institutional archive and tumor tissue was tested for point mutations in BRAF and RAS genes and for rearrangements in RET, NTRK1, NTRK3, ALK, PPARG, BRAF and THADA. A total of 163 PTCs were analyzed. Point mutations were found in 83 (51%) and gene fusions in 48 cases (30%). The most frequent alteration was the BRAFV600E mutation (36.8%), followed by NTRK3 fusion (11%), NRAS mutation (10.4%) and RET fusion (10.4%). Fusion-driven PTCs showed more frequently infiltrative growth, larger tumors, extrathyroidal extension and N1b disease. PTCs showing solid growth pattern were significantly enriched in gene fusions. This is one of the largest cohorts of pediatric PTCs. Fusion-driven tumors most frequently show aggressive pathological features; the search for rearrangements, especially in tumors with solid areas, could improve the characterization of pediatric PTCs and offer possible therapeutic options.

Communicating with residents about 10 years of scientific progress in understanding thyroid cancer risk in children after the Fukushima Dai-ichi Nuclear Power Station accident

After the Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident in 2011, radiation-related risk of childhood thyroid cancer remains a matter of concern among residents living in areas affected by radioactive plumes. As a countermeasure to that, the Fukushima Prefectural Government-in conjunction with Fukushima Medical University-began the Fukushima Thyroid Examination (FTE) campaign in 2011. As 116 definite or suspected thyroid cancer cases were found after the first round of FTE and the total number of cases was >240 as of June 2020, residents' concerns have deepened. Some researchers claim that these cases are radiation-induced, while others claim a screening effect (because FTE uses high-resolution ultrasound equipment) and express concern about over-diagnosis. Researchers therefore must address two conflicting issues: one is to elucidate radiation effects on thyroid cancer, which requires continuation of FTE; the other is to solve ethical problems associated with FTE. As to over-diagnosis, surgeons claim that early diagnosis benefits children by reducing the side-effects of treatment and prolonging disease-free survival, while cancer epidemiologists claim that early diagnosis will result in overtreatment without reducing the death rate. 'To receive FTE or not' and 'to stop FTE or not' are ongoing dilemmas for children (and their parents) and other stakeholders, respectively. To facilitate building a consensus among stakeholders, I overview recent findings about dose reconstruction, the dose-response relationship of thyroid cancer, over-diagnosis, and the natural history of thyroid cancer, all of which contribute to judging the risk-benefit balance of thyroid screening.

Recent advances in radiobiology with respect to pleiotropic aspects of tissue reaction

DNA double-strand breaks (DSBs) induced by ionizing radiation are the major cause of cell death, leading to tissue/organ injuries, which is a fundamental mechanism underlying the development of tissue reaction. Since unscheduled senescence, predominantly induced among epithelial tissues/organs, is one of the major modes of cell death in response to radiation exposure, its role in tissue reaction has been extensively studied, and it has become clear that senescence-mediated secretion of soluble factors is an indispensable component of the manifestation of tissue reaction. Recently, an unexpected link between cytoplasmic DSBs and innate immunity was discovered. The activation of cyclic GMP-AMP (cGAMP) synthase (cGAS) results in the stimulation of the cGAS-stimulator of interferon genes (STING) pathway, which has been shown to regulate the transactivation of a variety of secretory factors that are the same as those secreted from senescent cells. Furthermore, it has been proven that cGAS-STING pathway also mediates execution of the senescence process by itself. Hence, an autocrine/paracrine feedback loop has been discussed in previous literature in relation to its effect on the tissue microenvironment. As the tissue microenvironment plays a crucial role in cancer development, tissue reaction could be involved in the late health effects caused by radiation exposure. In this paper, the novel findings in radiation biology, which should provide a better understanding of the mechanisms underlying radiation-induced carcinogenesis, are overviewed.

Molecular pathogenesis of pediatric thyroid carcinoma

There has been little understanding of the molecular pathogenesis of pediatric thyroid cancers. Most of them are histologically classified as papillary thyroid carcinoma (PTC). Ionizing radiation is the most important environmental factor to induce PTC, especially in children. Particularly, radiation-related pediatric PTCs after the Chernobyl accident provided invaluable information. In addition, the recent accumulation of sporadic pediatric PTC cases, partly due to advances in diagnostic imaging, has also provided insight into their general pathogenesis. In PTC development, basically two types of genetic alterations, fusion oncogenes, mainly RET/PTC, and a point mutation, mainly BRAFV600E, are thought to play a key role as driver oncogenes. Their frequencies vary depending on patient age. The younger the age, the more prevalent the fusion oncogenes are. Higher incidence of fusion oncogenes was also observed in cases exposed to radiation. In short, fusion oncogenes are associated with both age and radiation and are not evidence of radiation exposure. The type of driver oncogene is shifted toward BRAFV600E during adolescence in sporadic PTCs. However, until about this age, fusion oncogenes seem to still confer dominant growth advantages, which may lead to the higher discovery rate of the fusion oncogenes. It has been postulated that RET/PTC in radiation-induced PTC is generated by ionizing radiation; however, there is an interesting hypothesis that thyroid follicular cell clones with pre-existing RET/PTC were already present, and radiation may play a role as a promoter/progressor but not initiator. Telomerase reverse transcriptase gene (TERT) promoter mutations, which are the strongest marker of tumor aggressiveness in adult PTC cases, have not been detected in pediatric cases; however, TERT expression without the mutations may play a role in tumor aggressiveness. In this paper, the recent information regarding molecular findings in sporadic and radiation-associated pediatric PTCs is summarized.

Intratumoral Heterogeneity in Differentiated Thyroid Tumors: An Intriguing Reappraisal in the Era of Personalized Medicine

Differentiated thyroid tumors (DTTs) are characterized by significant molecular variability in both spatial and temporal intra-tumoral heterogeneity (ITH), that could influence the therapeutic management. ITH phenomenon appears to have a relevant role in tumor growth, aggressive behavior and drug resistance. Accordingly, characteristics and consequences of ITH in DTTs should be better analyzed and understood in order to guide clinical practice, improving survival. Consequently, in the present review, we investigated morphological and molecular ITH of DTTs in benign, borderline neoplasms and in malignant entities, summarizing the most significant data. Molecular testing in DTTs documents a high risk for recurrence of cancer associated with BRAF^V600E, RET/PTC 1/3, ALK and NTRK fusions, while the intermediate risk may be related to BRAF^K601E, H/K/N RAS and PAX8/PPARγ. In addition, it may be suggested that tumor genotype is associated with peculiar phenotype.

Complete response to larotrectinib treatment in a patient with papillary thyroid cancer harboring an ETV6-NTRK3 gene fusion

Larotrectinib, a highly selective TRK inhibitor, was administered to a patient with rapidly progressing radioactive iodine-refractory papillary NTRK3 fusion-positive thyroid cancer. The patient achieved a durable (sustained for 11 months) complete response after 2 months of treatment and complete intracranial responses in metastatic brain lesions after 7 months of treatment. Larotrectinib may provide a therapeutic route for patients with RAI-R-differentiated thyroid cancer who might otherwise have few treatment options.

Genomic profile of columnar cell variant of papillary thyroid carcinoma

BACKGROUND AND AIMS

Columnar cell variant (CCV) is a rare papillary thyroid carcinoma subtype. The majority of CCV occur in older patients and are large, invasive tumours that pursue an aggressive clinical course. Rare well-circumscribed CCV occur in younger female patients and are comparatively indolent.

METHODS AND RESULTS

We retrospectively identified CCV with material available to perform targeted next-generation sequencing and correlated molecular results with clinicopathological features and outcome. Our cohort was comprised of nine CCV. Nearly all were aggressive tumours; however, one was predominantly well-circumscribed and arose in a thyroglossal duct cyst of a 26-year-old woman who had no evidence of disease at last follow-up. Seven (78%) cases demonstrated activating oncogenic driver alterations in BRAF, including BRAF V600E, an activating N486_P490del deletion, and BRAF-AGK fusions. Activating RAS mutations were seen in two (22%) cases. Additionally, three (33%) cases had TERT promoter mutations, four (44%) had loss of the tumour suppressor CDKN2A and one (11%) case had a loss of function TP53 mutation. Most cases (89%) also demonstrated copy number alterations, including recurrent gain of chromosome 1q (five cases) and losses of chromosome 9p (three cases) and 22q (four cases). The one case without secondary pathogenic mutations or copy number alterations was the tumour in the 26-year-old woman.

CONCLUSIONS

We found that CCV is primarily a BRAF-driven tumour, with most also harbouring secondary oncogenic mutations and multiple chromosomal gains and losses. Moreover, our findings suggest that molecular analysis could potentially be used to help risk stratify CCV.

Distant Metastases From Childhood Differentiated Thyroid Carcinoma: Clinical Course and Mutational Landscape

CONTEXT

Distant metastases (DM) from childhood differentiated thyroid carcinoma (DTC) are uncommon and published studies are limited.

OBJECTIVE

This work aimed to describe the outcomes of patients with DM from childhood DTC and to evaluate the molecular landscape of these tumors.

METHODS

A retrospective study was conducted at a tertiary cancer center including patients with pediatric DTC (diagnosed at age ≤ 18 years from 1946 to 2019) and DM.

RESULTS

We identified 148 patients; 144 (97%) had papillary thyroid carcinoma (PTC) and 104 (70%) were female. Median age at DTC diagnosis was 13.4 years (interquartile range [IQR], 9.9-15.9 years). Evaluable individuals received a median of 2 (IQR, 1-3) radioactive iodine (RAI) treatments at a median cumulative administered activity of 238.0 mCi (IQR, 147.5-351.0 mCi). The oncogenic driver was determined in 64 of 69 PTC samples: RET fusion (38/64; 59%), NTRK1/3 fusions (18/64; 28%), and the BRAF V600E mutation (8/64; 13%). At last evaluation, 93% had persistent disease. The median overall and disease-specific survival after DTC diagnosis were 50.7 and 52.8 years, respectively. Eight (5%) PTC patients died of disease after a median of 30.7 years (IQR, 20.6-37.6 years).

CONCLUSION

Childhood DTC with DM persists in most patients despite multiple courses of RAI, but disease-specific death is uncommon, typically occurring decades after diagnosis. Fusion genes are highly prevalent in PTC, and all identified molecular alterations have appropriate targeted therapies. Future studies should focus on expanding genotype-phenotype correlations, determining how to integrate molecularly targeted therapy into treatment paradigms, and relying less on repeated courses of RAI to achieve cure in patients with DM from childhood DTC.

A Multifocal Pediatric Papillary Thyroid Carcinoma (PTC) Harboring the AGK-BRAF and RET/PTC3 Fusion in a Mutually Exclusive Pattern Reveals Distinct Levels of Genomic Instability and Nuclear Organization

Simple Summary

Genetic alterations, such as RET/PTC and AGK-BRAF fusions, are frequent events in pediatric papillary thyroid carcinoma (PTC). However, their role as prognostic markers in pediatric PTC is still under investigation. In this study, we present a patient harboring three tumor foci with distinct genetic alterations (AGK-BRAF, RET/PTC3 and an absence of canonical alterations) that were investigated for DNA structure and telomere-related genomic instability. These preliminary results highlight that AGK-BRAF fusion likely affects nuclear architecture, which might explain a more aggressive disease outcome observed in pediatric PTC cases with AGK-BRAF fusion.

Abstract

The spectrum and incidence of gene fusions in papillary thyroid carcinoma (PTC) can differ significantly depending on the age of onset, histological subtype or radiation exposure history. In sporadic pediatric PTC, RET/PTC1-3 and AGK-BRAF fusions are common genetic alterations. The role of RET/PTC as a prognostic marker in pediatric PTC is still under investigation. We recently showed that AGK-BRAF fusion is prevalent in young patients (mean 10 years) and associated with specific and aggressive pathological features such as multifocality and lung metastasis. In this pilot study, we report a unique patient harboring three different foci: the first was positive for AGK-BRAF fusion, the second was positive for just RET/PTC3 fusion and the third was negative for both rearrangements. To investigate whether AGK-BRAF and RET/PTC3 are associated with genomic instability and chromatin modifications, we performed quantitative fluorescence in situ hybridization (Q-FISH) of telomere repeats followed by 3D imaging analysis and 3D super-resolution Structured Illumination Microscopy (3D-SIM) to analyze the DNA structure from the foci. We demonstrated in this preliminary study that AGK-BRAF is likely associated with higher levels of telomere-related genomic instability and chromatin remodeling in comparison with RET/PTC3 foci. Our results suggest a progressive disruption in chromatin structure in AGK-BRAF-positive cells, which might explain a more aggressive disease outcome in patients harboring this rearrangement.

Integrated DNA and RNA sequencing reveals targetable alterations in metastatic pediatric papillary thyroid carcinoma

BACKGROUND

Pediatric papillary thyroid carcinoma (PTC) is clinically and biologically distinct from adult PTC. We sequenced a cohort of clinically annotated pediatric PTC cases enriched for high-risk tumors to identify genetic alterations of relevance for diagnosis and therapy.

METHODS

Tumor DNA and RNA were extracted from FFPE tissue and subjected to next-generation sequencing (NGS) library preparation using a custom 124-gene hybridization capture panel and the 75-gene Archer Oncology Research Panel, respectively. NGS libraries were sequenced on an Illumina MiSeq.

RESULTS

Thirty-six pediatric PTC cases were analyzed. Metastases were frequently observed to cervical lymph nodes (29/36, 81%), with pulmonary metastases less commonly found (10/36, 28%). Relapsed or refractory disease occurred in 18 patients (18/36, 50%). DNA sequencing revealed targetable mutations in 8 of 31 tumors tested (26%), most commonly BRAF p.V600E (n = 6). RNA sequencing identified targetable fusions in 13 of 25 tumors tested (52%): RET (n = 8), NTRK3 (n = 4), and BRAF. Mutually exclusive targetable alterations were discovered in 15 of the 20 tumors (75%) with both DNA and RNA analyzed. Fusion-positive PTC was associated with multifocal disease, higher tumor staging, and higher American Thyroid Association risk levels. Both BRAF V600E mutations and gene fusions were correlated with the presence of cervical metastases.

CONCLUSIONS

Targetable alterations were identified in 75% of pediatric PTC cases with both DNA and RNA evaluated. Inclusion of RNA sequencing for detection of fusion genes is critical for evaluation of these tumors. Patients with fusion-positive tumors were more likely to have features of high-risk disease.

RET, NTRK, ALK, BRAF, and MET Fusions in a Large Cohort of Pediatric Papillary Thyroid Carcinomas

Background: Pediatric papillary thyroid carcinoma (PTC) is a rare malignancy, but with increasing incidence. Pediatric PTCs have distinct clinical and pathological features and even the molecular profile differs from adult PTCs. Somatic point mutations in pediatric PTCs have been previously described and studied, but complex information about fusion genes is lacking. The aim of this study was to identify different fusion genes in a large cohort of pediatric PTCs and to correlate them with clinical and pathological data of patients. Methods: The cohort consisted of 93 pediatric PTC patients (6-20 years old). DNA and RNA were extracted from fresh frozen tissue samples, followed by DNA and RNA-targeted next-generation sequencing analyses. Fusion gene-positive samples were verified by real-time polymerase chain reaction. Results: A genetic alteration was found in 72/93 (77.4%) pediatric PTC cases. In 52/93 (55.9%) pediatric PTC patients, a fusion gene was detected. Twenty different types of RET, NTRK3, ALK, NTRK1, BRAF, and MET fusions were found, of which five novel, TPR/RET, IKBKG/RET, BBIP1/RET, OPTN/BRAF, and EML4/MET, rearrangements were identified and a CUL1/BRAF rearrangement that has not been previously described in thyroid cancer. Fusion gene-positive PTCs were significantly associated with the mixture of classical and follicular variants of PTC, extrathyroidal extension, higher T classification, lymph node and distant metastases, chronic lymphocytic thyroiditis, and frequent occurrence of psammoma bodies compared with fusion gene-negative PTCs. Fusion-positive patients also received more doses of radioiodine therapy. The most common fusion genes were the RET fusions, followed by NTRK3 fusions. RET fusions were associated with more frequent lymph node and distant metastases and psammoma bodies, and NTRK3 fusions were associated with the follicular variant of PTC. Conclusions: Fusion genes were the most common genetic alterations in pediatric PTCs. Fusion gene-positive PTCs were associated with more aggressive disease than fusion gene-negative PTCs.

Clinicopathologic features of kinase fusion-related thyroid carcinomas: an integrative analysis with molecular characterization

The discovery of actionable kinase gene rearrangements has revolutionized the therapeutic landscape of thyroid carcinomas. Unsolved challenges include histopathologic recognition of targetable cases, correlation between genotypes and tumor behavior, and evolving resistance mechanisms against kinase inhibitors (KI). We present 62 kinase fusion-positive thyroid carcinomas (KFTC), including 57 papillary thyroid carcinomas (PTC), two poorly differentiated thyroid carcinomas (PDTC), two undifferentiated thyroid carcinomas (ATC), and one primary secretory carcinoma (SC), in 57 adults and 5 adolescents. Clinical records, post-operative histology, and molecular profiles were reviewed. Histologically, all KFTC showed multinodular growth with prominent intratumoral fibrosis. Lymphovascular invasion (95%), extrathyroidal extension, gross and microscopic (63%), and cervical lymph node metastasis (79%) were common. Several kinase fusions were identified: STRN-ALK, EML4-ALK, AGK-BRAF, CUL1-BRAF, MKRN1-BRAF, SND1-BRAF, TTYH3-BRAF, EML4-MET, TFG-MET, IRF2BP2-NTRK1, PPL-NTRK1, SQSTM1-NTRK1, TPR-NTRK1, TPM3-NTRK1, EML4-NTRK3, ETV6-NTRK3, RBPMS-NTRK3, SQSTM1-NTRK3, CCDC6-RET, ERC1-RET, NCOA4-RET, RASAL2-RET, TRIM24-RET, TRIM27-RET, and CCDC30-ROS1. Individual cases also showed copy number variants of EGFR and nucleotide variants and indels in pTERT, TP53, PIK3R1, AKT2, TSC2, FBXW7, JAK2, MEN1, VHL, IDH1, PTCH1, GNA11, GNAQ, SMARCA4, and CDH1. In addition to thyroidectomy and radioactive iodine, ten patients received multi-kinase and/or selective kinase inhibitor therapy, with 6 durable, objective responses and four with progressive disease. Among 47 cases with >6 months of follow-up (median [range]: 41 [6-480] months), persistent/recurrent disease, distant metastasis and thyroid cancer-related death occurred in 57%, 38% and 6%, respectively. In summary, KFTC encompass a spectrum of molecularly diverse tumors with overlapping clinicopathologic features and a tendency for clinical aggressiveness. Characteristic histology with multinodular growth and prominent fibrosis, particularly when there is extensive lymphovascular spread, should trigger molecular testing for gene rearrangements, either in a step-wise manner by prevalence or using a combined panel. Further, our findings provide information on molecular therapy in radioiodine-refractory thyroid carcinomas.

Genetic Landscape of Papillary Thyroid Carcinoma and Nuclear Architecture: An Overview Comparing Pediatric and Adult Populations

Thyroid cancer is a rare malignancy in the pediatric population that is highly associated with disease aggressiveness and advanced disease stages when compared to adult population. The biological and molecular features underlying pediatric and adult thyroid cancer pathogenesis could be responsible for differences in the clinical presentation and prognosis. Despite this, the clinical assessment and treatments used in pediatric thyroid cancer are the same as those implemented for adults and specific personalized target treatments are not used in clinical practice. In this review, we focus on papillary thyroid carcinoma (PTC), which represents 80-90% of all differentiated thyroid carcinomas. PTC has a high rate of gene fusions and mutations, which can influence the histologic subtypes in both children and adults. This review also highlights telomere-related genomic instability and changes in nuclear organization as novel biomarkers for thyroid cancers.

Response to RET-Specific Therapy in RET Fusion-Positive Anaplastic Thyroid Carcinoma

Background: Anaplastic thyroid carcinoma (ATC) remains one of the most challenging malignancies to treat in the modern era. Most patients present with or develop recurrent/metastatic incurable disease with poor response rates to conventional chemotherapy, and life expectancy is short. Next-generation sequencing (NGS) can be leveraged in ATC to identify oncogenic alterations that can be targeted with molecularly specific therapy, offering new effective treatment options to a subset of patients. Patient Findings: A 73-year-old man presenting with locally advanced papillary thyroid carcinoma containing a minor component of ATC was treated with surgery and iodine-131. He developed biopsy-confirmed ATC distant metastases that progressed on cytotoxic chemotherapy. NGS revealed several alterations, including a CCDC6-RET gene fusion. The patient enrolled in LIBRETTO-001, a phase I/II trial of the potent and specific RET inhibitor, LOXO-292. The patient tolerated LOXO-292 well and experienced a deep and durable partial response, ongoing beyond 19 months. Conclusion: This clinically significant response achieved with LOXO-292 in a patient with a CCDC6-RET fusion-positive ATC who had exhausted conventional treatment options highlights the importance of conducting tumor genomic profiling in patients with ATC to identify uncommon but actionable genomic alterations, such as RET gene fusions.

Comparison of pediatric and adult medullary thyroid carcinoma based on SEER program

To compare the clinicopathological characteristics and survival outcomes of children and adult diagnosed with medullary thyroid carcinoma (MTC). MTC patients were extracted from the Surveillance, Epidemiology and End Results (SEER) database from 1998 to 2016, followed by stratification into pediatric (< 20 years) or adult (≥ 20 years) groups. In total, 2,197 patients (110 pediatric and 2087 adult) with MTC were identified. Pediatric patients were more likely to have localized stage (70.0% vs. 51.6%), negative regional nodes (48.2% vs. 30.8%) and receive total/subtotal thyroidectomy surgery (97.3% vs. 85.3%). Moreover, CSS and OS rates were significantly higher in pediatric patients (both P < 0.001). Multivariable Cox regression analysis revealed that adult patients were significantly correlated with worse CSS and OS rates [(CSS: HR 11.60, 95% CI 1.62–83.02, P = 0.015); (OS: HR 5.63, 95% CI 2.08–15.25, P = 0.001)]. Further stratified analysis indicated that pediatric group might have significant better CSS and OS for patients with more advanced stage. Patients in the pediatric group were more likely to have earlier stage. Moreover, the prognosis of pediatric MTC patients was significantly better than that in adult patients.

Predominant DICER1 Pathogenic Variants in Pediatric Follicular Thyroid Carcinomas

Background: Pediatric thyroid cancer has characteristics that are distinct from adulthood thyroid cancer. Due to its very low prevalence, little is known about the genetic characteristics of pediatric follicular thyroid cancer (FTC). Methods: We investigated genetic alterations in tumor tissues from 15 patients aged <20 years (median: 14.3 years; range: 2.4 - 19.0 years) using multifaceted approaches. Whole-exome sequencing, targeted next-generation sequencing using a cancer gene panel, and Sanger sequencing of the major exons of the H/K/N-RAS and DICER1 genes and the promoter region of the TERT gene were performed. Normal tissues or blood of patients with DICER1- or PTEN-positive tumors was also evaluated to determine whether the variant is germ line. Results: The median tumor size was 3.1 cm (range: 0.6 - 6.4 cm). Four patients exhibited angioinvasion and one extensive capsular invasion; none showed evidence of disease over a median of 8.1 years. Eight patients (53.3%) had DICER1 variants, including four with DICER1 syndrome (three patients were <10 years of age). One patient had a germ line PTEN frameshift variant with the diagnosis of PTEN hamartoma tumor syndrome. One patient had a PAX8/PPARγ rearrangement, and two patients had no genetic driver alteration other than multiple loss of heterozygosity with or without copy number alterations in their tumors. No RAS or TERT variants were found. Nodular hyperplasia and follicular adenoma (FA) coexisted in DICER1 variant-positive FTCs more frequently than variant-negative FTCs (p = 0.026). All DICER1 variant-positive FTCs had a somatic missense variant at metal binding sites (six at codon p.E1813 and two at codon p.D1709) within the RNase IIIb domain; seven had other missense, nonsense, or frameshift variants in the DICER1 gene. Six coexisting FAs of two patients with DICER1 syndrome (three of each) had additional somatic variants at metal binding sites within the RNase IIIb domain (codon p.E1705, p.D1709, p.D1810, or p.E1813), different from each other and from the indexed FTC tumor. Conclusions: Pediatric FTCs have distinct genomic alterations and pathogenesis compared with adults, particularly those characterized by DICER1 variants. The DICER1 variant should be considered in pediatric FTCs, especially in cases <10 years of age. In all DICER1 variant-positive FTCs and FAs, recurrent hotspot variants were found at metal binding sites within the RNase IIIb domain, suggesting they impact tumorigenesis.

Thyroid carcinoma in children, adolescents, and young adults in Brazil: A report from 11 population-based cancer registries

Background

The increasing incidence of thyroid cancer has been described worldwide. Overdiagnosis, improved imaging, and increased environmental risk factors have contributed to the rising incidence. The objective of this study was to analyze the population incidence rate and trends during the period of 2000–2013 in children, adolescents and young adults (AYAs) in Brazil.

Methods

Data were extracted from 11 population-based cancer registries (PBCRs) encompassing the five geographic regions of Brazil. Incidence rates per million in children (0–14) and AYAs (15–39) according to world population were analyzed according to sex, age, and type of carcinoma. Incidence trends were evaluated using joinpoint regression.

Results

During 2000 to 2013, we identified 11,081 children and AYAs (0–39 years) with thyroid carcinoma in 11 PBCRs, with an age-adjusted incidence rate (AAIR) of 42 cases per million. Females had a higher AAIR of 66 cases per million versus 14 cases per million in males. Age-specific incidence rate (ASR) increased with age. Geographic variation was also observed; the Midwest and Southeast regions had the highest ASR in all age groups. The lowest ASR in all age groups was seen in the North region. Papillary subtype was the most common. Overall, the incidence rates in children and AYAs significantly increased from 0.2 in 2000 to 2.8 in 2013 and from 47.1 to 115.3, respectively, with an annual average percent change of 18.8 [8.1; 30.6] for children and 7.9 [CI 5.6; 10.3] for AYAs.

Conclusions

Rates of thyroid cancer, particularly the papillary subtype, are steadily increasing in children and AYAs, especially among females. There are variations among geographic areas. This increased incidence is unlikely to be explained by screening, as children less than 14 years of age do not typically undergo medical surveillance. Environmental risk factors must be investigated.

RET Gene Fusions in Malignancies of the Thyroid and Other Tissues

Following the identification of the BCR-ABL1 (Breakpoint Cluster Region-ABelson murine Leukemia) fusion in chronic myelogenous leukemia, gene fusions generating chimeric oncoproteins have been recognized as common genomic structural variations in human malignancies. This is, in particular, a frequent mechanism in the oncogenic conversion of protein kinases. Gene fusion was the first mechanism identified for the oncogenic activation of the receptor tyrosine kinase RET (REarranged during Transfection), initially discovered in papillary thyroid carcinoma (PTC). More recently, the advent of highly sensitive massive parallel (next generation sequencing, NGS) sequencing of tumor DNA or cell-free (cfDNA) circulating tumor DNA, allowed for the detection of RET fusions in many other solid and hematopoietic malignancies. This review summarizes the role of RET fusions in the pathogenesis of human cancer.

Recurrence and Complications in Pediatric and Adolescent Papillary Thyroid Cancer in a High-Volume Practice

BACKGROUND

Treatment approaches for pediatric papillary thyroid cancer (PTC) are historically extrapolated from adult experience. However, pediatric PTC demonstrates a greater propensity for lymph node involvement, early metastases, and recurrence, highlighting the need for pediatric-specific treatment paradigms.

MATERIALS AND METHODS

A retrospective review included patients with PTC aged ≤21 y, with ≥18 mo of follow-up, treated between 2002 and 2015. Fisher's exact test and Cox proportional hazard were used to estimate the effect of risk factors on disease recurrence.

RESULTS

Seventy-two cases of PTC were identified with median age of 17.0 y and median follow-up of 64.1 mo. Disease recurred at a median of 24.6 mo (range 7.8-78.1) in 7 of 51 (13.7%) of patients with disease limited to the thyroid or central neck, 7 of 18 (39%) patients with lateral neck disease at presentation who underwent a compartment-based resection, and three of three patients (100%) with lateral neck disease who sought care after non-compartment-based resection. There were no deaths from disease. Univariate predictors of recurrence included tumor size >2 cm (P = 0.005), lateral neck disease (P = 0.004), lymphovascular invasion (P = 0.017), extracapsular invasion (P < 0.0001), multifocality (P = 0.03), and non-Caucasian race (P = 0.05). Multivariate analysis identified race (P = 0.05) as an independent predictor of recurrence. In patients without lateral neck disease, there was a trend toward lower recurrence in patients undergoing thyroidectomy with central neck dissection compared with thyroidectomy alone (P = 0.07).

CONCLUSIONS

Pediatric PTC is associated with excellent survival, although recurrence is common in patients with lateral node involvement. Predictors of recurrence are multifactorial and may be influenced by extent of disease, patient or tumor biology, and aggressiveness of resection.

LEVEL OF EVIDENCE

Prognosis study, level IV, retrospective case series.

Revised criteria for diagnosis of NIFTP reveals a better correlation with tumor biological behavior

The recent reclassification of a follicular variant of papillary thyroid carcinoma (FVPTC), subset as noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), aims to avoid overtreatment of patients with an indolent lesion. The diagnosis of NIFTP has recently been revisited using more rigid criteria. This study presents histological and molecular findings and a long clinical follow-up of 94 FVPTC, 40 cases of follicular adenoma (FTA) and 22 cases of follicular carcinoma (FTC) that were classified before the advent of the NIFTP reclassification. All slides were reviewed using these rigid criteria and analysis of numerous sections of paraffin blocks and reclassified as 7 NIFTPs, 2 EFVPTCs, 29 infiltrative FVPTC (IFVPTCs), 57 invasive EFVPTC (I-EFVPTCs), 39 FTAs and 22 FTCs. Remarkably, EFVPTC and NIFTP patients were all free of disease at the end of follow-up and showed no BRAF mutation. Only one NIFTP sample harbored mutations, an NRAS Q61R. PAX8/PPARG fusion was found in I-EFVPTCs and FTC. Although additional studies are needed to identify a specific molecular profile to aid in the diagnosis of lesions with borderline morphological characteristics, we confirmed that the BRAF V600E mutation is an important tool to exclude the diagnosis of NIFTP. We also show that rigorous histopathological criteria should be strongly followed to avoid missing lesions in which more aggressive behavior is present, mainly via the analysis of capsule or vascular invasion and the presence of papillary structures.

TRK Inhibition: A New Tumor-Agnostic Treatment Strategy

Oncogenic somatic chromosomal rearrangements involving the NTRK1, NTRK2 or NTRK3 genes (NTRK gene fusions) occur in up to 1% of all solid tumors, and have been reported across a wide range of tumor types. The fusion proteins encoded by such rearranged sequences have constitutively activated TRK tyrosine kinase domains, providing novel therapeutic anticancer targets. The potential clinical effectiveness of TRK inhibition in patients with tumors harboring NTRK gene fusions is being assessed in phase I and II trials of TRK inhibitors, such as larotrectinib and entrectinib. Clinical trial results have demonstrated that larotrectinib is generally well tolerated and has shown high response rates that are durable across tumor types. These data validate NTRK gene fusions as actionable genomic alterations. In this review, we present the clinical data, discuss the different approaches that might be used to routinely screen tumors to indicate the presence of NTRK gene fusions, explore the issue of acquired resistance to TRK inhibition, and reflect on the wider regulatory considerations for tumor site agnostic TRK inhibitor drug development.

Thyroid Cancer in the Pediatric Population

Thyroid cancer is rare in the pediatric population, but thyroid carcinomas occurring in children carry a unique set of clinical, pathologic, and molecular characteristics. In comparison to adults, children more often present with aggressive, advanced stage disease. This is at least in part due to the underlying biologic and molecular differences between pediatric and adult thyroid cancer. Specifically, papillary thyroid carcinoma (which accounts for approximately 90% of pediatric thyroid cancer) has a high rate of gene fusions which influence the histologic subtypes encountered in pediatric thyroid tumors, are associated with more extensive extrathyroidal disease, and offer unique options for targeted medical therapies. Differences are also seen in pediatric follicular thyroid cancer, although there are few studies of non-papillary pediatric thyroid tumors published in the literature due to their rarity, and in medullary carcinoma, which is most frequently diagnosed in the pediatric population in the setting of prophylactic thyroidectomies for known multiple endocrine neoplasia syndromes. The overall shift in the spectrum of histotypes and underlying molecular alterations common in pediatric thyroid cancer is important to recognize as it may directly influence diagnostic test selection and therapeutic recommendations.

Radiation-Induced Thyroid Cancers: Overview of Molecular Signatures

Enormous amounts of childhood thyroid cancers, mostly childhood papillary thyroid carcinomas (PTCs), after the Chernobyl nuclear power plant accident have revealed a mutual relationship between the radiation exposure and thyroid cancer development. While the internal exposure to radioactive ¹³¹I is involved in the childhood thyroid cancers after the Chernobyl accident, people exposed to the external radiation, such as atomic-bomb (A-bomb) survivors, and the patients who received radiation therapy, have also been epidemiologically demonstrated to develop thyroid cancers. In order to elucidate the mechanisms of radiation-induced carcinogenesis, studies have aimed at defining the molecular changes associated with the thyroid cancer development. Here, we overview the literatures towards the identification of oncogenic alterations, particularly gene rearrangements, and discuss the existence of radiation signatures associated with radiation-induced thyroid cancers.

AGK-BRAF is associated with distant metastasis and younger age in pediatric papillary thyroid carcinoma

BACKGROUND

The incidence of thyroid carcinoma has increased in most populations, including pediatric patients. The increase is almost exclusively due to an increase in the incidence of papillary thyroid carcinoma (PTC). Genetic alterations leading to mitogen-activated protein kinase (MAPK) pathway activation are highly prevalent in PTC, with BRAF V600E mutation being the most common event in adult PTC. Although a lower prevalence of BRAF V600E had been reported among pediatric patients, a higher prevalence of BRAF fusion has been identified in both radiation-exposed and sporadic pediatric PTC. However, little is known about the prognostic implications of BRAF fusions in pediatric PTC.

PROCEDURE

In this study, we investigated the prevalence of BRAF alterations (AGK-BRAF fusion and BRAF V600E mutation) in a large set of predominantly sporadic pediatric PTC cases and correlate with clinicopathological features. Somatic AGK-BRAF fusion was investigated by RT-PCR and confirmed by FISH break-apart. The BRAF V600E mutation was screened using Sanger sequencing.

RESULTS

AGK-BRAF fusion, found in 19% of pediatric PTC patients, was associated with distant metastasis and younger age. Conversely, the BRAF V600E, found in 15% of pediatric PTC patients, was correlated with older age and larger tumor size.

CONCLUSION

Collectively, our results advance knowledge concerning genetic bases of pediatric thyroid carcinoma, with potential implications for diagnosis, prognosis, and therapeutic approaches.

Radiation-induced papillary thyroid cancer: is it a distinct clinical entity?

PURPOSE OF REVIEW

To present the current status of knowledge regarding radiation-induced papillary thyroid cancer (RIPTC), defining its epidemiologic, pathologic, and clinical characteristics, with ensuing possible therapeutic and prognostic consequences.

RECENT FINDINGS

Cumulative evidence shows that RIPTC resembles sporadic papillary thyroid cancer (PTC) of comparable age, both in terms of clinical-pathological features and prognosis. Therefore, more aggressive treatment does not seem to be required when managing RIPTC as its prognosis is comparable to that of never-irradiated patients.

SUMMARY

Radiation exposure in childhood is a well-documented risk factor for development of PTC. Therefore, increased exposure to medical or environmental radiation may be in part responsible, along with increased screening, of the recent burgeoning incidence of PTC. A specific morphological and molecular portrait of RIPTC is unlikely to exist. The more aggressive histologic and clinical features initially reported in radiation-induced cases are consistent with the expectations in nonradiation-related PTC of a comparable age. Aggressive histology, nodal, and distant metastases correlate with early age at onset rather than with radiation exposure. Although relapses are frequent in children, long-term cancer-specific mortality is approximately 1%, lower than that observed for adults and comparable between irradiated and nonirradiated cohorts. RIPTC does not require more aggressive surgery or more adjuvant treatments, as prognosis is as good as that of sporadic PTC when matched for stage and treatment received.

Evaluation of MEDAG gene expression in papillary thyroid microcarcinoma: associations with histological features, regional lymph node metastasis and prognosis

Papillary thyroid microcarcinoma accounts for a large proportion of papillary thyroid carcinoma, especially among new cases. Many  PTMC patients have regional lymph node metastasis, with some experiencing recurrence and even death. However, the risk factors and mechanism by which PTMC relates to these factors are unknown. In this study, differentially expressed genes were identified with microarray from The Cancer Genome Atlas, followed by analysis using the Kyoto Encyclopedia of Genes and Genomes. Immunohistochemistry, immunofluorescence, western blot and Oil Red O staining were carried out to evaluate expression levels and functional alterations. Mesenteric Estrogen Dependent Adipogenesis expression was observed in almost all cases of papillary thyroid microcarcinomas, and the location of expression was associated with histological subtype. High expression was correlated with metastasis and poor disease-free survival. Furthermore, the enrichment analysis indicated that Mesenteric Estrogen Dependent Adipogenesis expression may be associated with metabolic reprogramming to influence metastasis and prognosis. These findings contribute to a better understanding of how Mesenteric Estrogen Dependent Adipogenesis affects metastasis and the prognosis of papillary thyroid microcarcinoma patients and suggest that Mesenteric Estrogen Dependent Adipogenesis expression may be a novel prognostic marker in these patients. 

Differentiated Thyroid Carcinoma in Pediatric Age: Genetic and Clinical Scenario

Introduction: Follicular-derived differentiated thyroid carcinoma (DTC) is the most common endocrine and epithelial malignancy in children. The differences in the clinical and pathological features of pediatric vs. adult DTC could relate to a different genetic profile. Few studies are currently available in this issue, however, and most of them involved a limited number of patients and focused mainly on radiation-exposed populations. Materials and Methods: We considered 59 pediatric patients who underwent surgery for DTC between 2000 and 2017. RET/PTC rearrangement was investigated with fluorescent in situ hybridization and real-time polymerase chain reaction. Sequencing was used to analyze mutations in the BRAF, NRAS, PTEN, PIK3CA genes, and the TERT promoter. The pediatric patients' clinical and molecular features were compared with those of 178 adult patients. Results: In our pediatric sample, male gender and age <15 years coincided with more extensive disease and more frequent lymph node and distant metastases. Compared with adults, the pediatric patients were more likely to have lymph node and distant metastasis, and to need second treatments (p < 0.01). In all, 44% of the pediatric patients were found to carry molecular alterations. RET/PTC rearrangement was confirmed as the most frequent genetic alteration in childhood DTC (24.6%) and correlated with aggressive features. BRAFV600E was only identified in 16% of the pediatric DTCs, while NRASQ61R, NRASQ61K, and TERTC250T mutations were very rare. Conclusions: Pediatric DTC is more aggressive at diagnosis and more likely to recur than its adult counterpart. Unlike the adult disease, point mutations have no key genetic role.

Response to Lenvatinib in Children with Papillary Thyroid Carcinoma

BACKGROUND

Papillary thyroid carcinoma (PTC) is the most common thyroid malignancy in children and adolescents. Infrequently, children with PTC may present with or develop disease not amenable to surgery or radioactive iodine (RAI), and systemic therapy may be an option. Lenvatinib is an oral tyrosine kinase inhibitor that is approved by the Food and Drug Administration for the treatment of adults with locally recurrent or metastatic, progressive, RAI-refractory well-differentiated thyroid carcinoma. The effect of lenvatinib in children with PTC has not been reported.

PATIENT FINDINGS

Three children with metastatic PTC not amenable or refractory to RAI who responded to lenvatinib are reported. All of them developed respiratory distress requiring oxygen caused by extensive bilateral metastatic pulmonary disease. The first patient is a 14-year-old female who was initially treated with sorafenib for extensive PTC not amenable to upfront surgery or RAI. She had progressive pulmonary disease after five months, and was subsequently treated with oral lenvatinib (14 mg/m²/day). She was weaned to room air after eight weeks. The second patient is a 15-year-old male who was treated with lenvatinib (14 mg/m²/day) for iodine non-avid diffuse pulmonary disease after initial total thyroidectomy and cervical lymph node dissection. He was weaned off oxygen in six weeks. The third patient is a five-year-old male who was treated with lenvatinib (14 mg/m²/day) for pulmonary disease progression 24 months after treatment with total thyroidectomy, cervical lymph node dissection, and RAI treatment. He was weaned off oxygen one day after starting lenvatinib. Two of the patients required dose adjustments secondary to proteinuria. Otherwise, all patients tolerated lenvatinib well. The first two patients remained clinically stable on lenvatinib 23 months and 11 months after initiation of therapy, respectively, and the third patient transitioned to a tumor-specific targeted therapy after one month.

SUMMARY

Three pediatric patients are reported with metastatic PTC not amenable or refractory to RAI who achieved a response on lenvatinib.

CONCLUSION

Lenvatinib therapy is well tolerated and demonstrated clinical activity in children with advanced PTC. Lenvatinib should be considered in children with PTC that is refractory or not amenable to conventional management.

LIMD2 Is Overexpressed in BRAF V600E-Positive Papillary Thyroid Carcinomas and Matched Lymph Node Metastases

We previously described that LIM domain containing 2 (LIMD2) overexpression was closely correlated with metastatic process in papillary thyroid carcinoma (PTC). We here evaluated the expression of LIMD2 in a series of non-metastatic and metastatic PTC and their matched lymph node metastases via immunohistochemistry. LIMD2 was expressed in 74 (81%) of primary PTC and 35 (95%) of lymph node metastases. Sub-analysis performed in 37 matched samples demonstrated that in four cases, LIMD2 is expressed in lymph node metastases, while it is not expressed in primary tumors. Moreover, in eight cases, the staining intensity of LIMD2 was stronger in the patient-matched lymph node metastases than in the primary tumors. Next, the expression of LIMD2 was correlated with clinical pathological parameters and BRAF V600E and RET/PTC mutational status. The expression of LIMD2 in primary tumors was correlated with the presence of BRAF V600E mutation (P = 0.0338). Western blot analysis in thyroid cell lines demonstrated that LIMD2 is expressed in two PTC cell lines, while it is not expressed in normal thyroid and follicular thyroid carcinoma cell lines. Importantly, its expression was higher in a PTC cell line that harbors BRAF V600E mutation than in a PTC cell line that harbors RET/PTC1. The available genomic profiling data generated by The Cancer Genome Atlas Research Network confirmed that LIMD2 expression is higher in BRAF-like PTC samples. Our data suggest that LIMD2 may play an important role in the metastatic process of PTC, predominantly in BRAF V600E-positive tumors.

Sporadic pediatric papillary thyroid carcinoma harboring the ETV6/NTRK3 fusion oncogene in a 7-year-old Japanese girl: a case report and review of literature

BACKGROUND

There have been great concerns about pediatric thyroid cancers after the accident at the Fukushima Daiichi Nuclear Power Plant in 2011.

CASE PRESENTATION

We report a case of a 7-year-old Japanese girl with sporadic papillary thyroid carcinoma (PTC) harboring an ETV6/NTRK3 rearrangement. The patient presented with tumors in both lobes and underwent thyroidectomy followed by radioactive iodine (RAI) ablation. Histopathology showed a classic type of PTC with cervical lymph node metastasis.

CONCLUSIONS

Genetic evaluation showed ETV6/NTRK3 fusion but no BRAF mutations or RET/PTC rearrangements. RET/PTC rearrangement and BRAF mutations often contribute to the pathogenesis of PTC; however, rearrangements of NTRK genes are relatively rare in pediatric PTC. Although NTRK rearrangement has been shown to often present unique pathological types and infiltrative architectures in the western population, such findings were not observed in this patient. Thus, the present case of classic PTC with ETV6/NTRK3 rearrangement highlights the disparate collection of clinic-pathological features compared to the trend in the western population. We therefore emphasize the need to further accumulate clinical as well as genetic data in pediatric PTCs.