Clinical and Molecular Characteristics May Alter Treatment Strategies of Thyroid Malignancies in DICER1 Syndrome

The common pathogenesis of nodular goiter in both sexes: An exploration into gene expression and signaling pathways

The past few years have witnessed an increasing incidence of nodular goiter (NG), with a well-documented higher prevalence in females than males. This gender disparity has led research to focus primarily on female subjects, potentially overlooking common pathogenic mechanisms in both sexes. In this study, we investigated the shared pathogenesis of NG in males and females. Utilizing a rat model and RNA sequencing, we identified differentially expressed genes associated with the disease. We further validated these findings in normal human thyroid cells and human papillary thyroid cancer cells. A randomized experiment was conducted with equal numbers of male and female rats divided into control and NG model groups. The NG model was established using propylthiouracil and various assessments such as thyroid ultrasonography, thyroid index, thyroid function, and thyroid histology were performed. Transcriptome analysis revealed numerous upregulated and downregulated genes in both male and female model groups. Key genes like KDR, FLT1, PDGFB, and CAV1, and pathways including PI3K-Akt, MAPK, Ras, fluid shear stress and atherosclerosis, calcium signaling, and Rap1 signaling pathways were linked with the disease. Western blot and immunofluorescence analysis confirmed these findings, which were further supported by cell-based experiments. In conclusion, our findings suggest that abnormal expression of specific genes and pathways leading to irregular cell growth, blood vessel formation, and inflammation may be common factors in the pathogenesis of NG in both males and females.

DICER1 Mutations Define the Landscape of Poorly Differentiated Thyroid Carcinoma in Children and Young Adults: Case Report and Literature Review

Poorly differentiated thyroid carcinoma (PDTC) is a rare malignancy, representing ~1% of all thyroid tumors. It is characterized by high-grade histologic features without the anaplastic characteristics observed in anaplastic thyroid carcinoma. Although rare in children and young adults, there is emerging evidence of clinical and genetic differences with PDTC in adults. We present a case of a 19-year-old female with a right thyroid lobe nodule classified as an EU-TIRADS 5 lesion. Subsequent FNAC showed a cellular aspirate of solitary cells and scant microfollicles with variable nuclear irregularities, which was designated a Bethesda class IV lesion. Thyroidectomy revealed histopathological features consistent with PDTC, including solid/trabecular growth, increased mitotic activity, central necrosis, and extensive vascular invasion. Molecular analysis identified germline and somatic DICER1 mutations in the absence of other established driver mutations of PDTC. This case report describes the fourth reported patient with a PDTC and germline DICER1 mutation. Our findings contribute to a limited body of literature on pediatric/young adult PDTC cases and highlight the pivotal role of DICER1 mutations. Emerging evidence suggests that pediatric PDTC may exhibit unique clinical and genetic characteristics, prompting further research into its molecular profile.

Prevalence, Molecular Landscape, and Clinical Impact of DICER1 and DGCR8 Mutated Follicular-Patterned Thyroid Nodules

BACKGROUND

Mutations in micro-RNA (miRNA) regulators DICER1 and DGCR8 have recently been uncovered, revealing a potential novel mechanism driving thyroid tumor development. However, the true frequency of these hotspot mutations in follicular-patterned thyroid tumors (FTs) and their relation to established driver gene events remain elusive.

METHODS

A total of 440 FTs from 2 institutions were interrogated for DICER1, DGCR8, and RAS family hotspot mutations using Sanger sequencing. Whole-exome sequencing was also performed to identify additional driver gene aberrations in DICER1/DGCR8-mutant cases. Subsets of cases were further analyzed using miRNA expression profiling, and key dysregulated miRNAs were validated as markers of DICER1 mutations using quantitative RT-PCR analysis. The Cancer Genome Atlas (TCGA) database was also probed for DICER1/DGCR8 mutations and miRNA dysregulation.

RESULTS

Fourteen (3.2%) and 4 (1%) FTs harbored DICER1 and DGCR8 hotspot mutations, respectively, in the combined cohort, and no cases with normal tissue available were found to exhibit a constitutional variant. Two DGCR8-mutant cases also harbored oncogenic RAS mutations. Whole-exome sequencing analysis did not identify additional driver gene events in DICER1/DGCR8-positive cases. Comprehensive miRNA expression profiling revealed a unique pattern of dysregulated miRNAs in DICER1/DGCR8-mutant cases compared with wild-type lesions. Moreover, DICER1-mutant cases showed a remarkable reduction of 5' arm miRNAs, findings corroborated in the TCGA cohort.

CONCLUSION

DICER1 and DGCR8 hotspot mutations are rare in unselected cohorts of FTs, and mutated cases exhibit a specific miRNA profile. Although DGCR8 mutations may coexist with established RAS gene alterations, FTs with DICER1 variants were devoid of other driver gene events.

Multi-UniFocality (MUF), in contrast to multifocality, in thyroid lesions: Relation to lymphocytic thyroiditis

Whereas multifocality typically concerns papillary thyroid carcinoma (PTC) without specification of intrathyroidal metastatic or independent nature of tumor foci, the designation of the latter as Multi-UniFocal (MUF) may be relevant for select cases. A case series involving multifocal thyroid lesions with divergent histopathological morphology and/or molecular profile, with molecular evaluation of multiple individual tumor foci per patient based on a next-generation sequencing approach, was retrospectively reviewed. Twenty-five patient cases with multifocal thyroid lesions suggestive of MUF, with 2-6 (median 3) tumor foci per patient, were described. Tumor lesions comprised diverse histopathology, including PTC, (E)FVPTC, NIFTP, FA, FTC, and oncocytic. Morphologically similar and/or diverse tumor foci harbored different molecular alterations (suggestive of non-shared clonality); with(out) coexistent similar foci harboring identical molecular alterations; or (partly) shared molecular alterations. MUF was associated with chronic lymphocytic thyroiditis in almost half of the cases. The recognition of MUF may justify the independent clinical consideration per individual tumor focus; as separate lesions albeit within a multifocal context. The potential clinical relevance and prognostic value of MUF remain to be further established.

DICER1 Mutations Occur in More Than One-Third of Follicular-Patterned Pediatric Papillary Thyroid Carcinomas and Correlate with a Low-Risk Disease and Female Gender Predilection

Some pediatric papillary thyroid carcinoma (PPTC) cohorts have suggested a preliminary correlation with respect to DICER1 mutation status and histomorphology in both benign and malignant follicular cell-derived nodules; however, the data regarding correlates of DICER1-related sporadic PPTCs subtyped based on the 2022 WHO classification criteria are largely unavailable. The current study investigated the status of hotspot DICER1 mutations with clinical, histological and outcome features in a series of 56 patients with PPTCs with no clinical or family history of DICER1-related syndromic manifestation. Fifteen (27%) PPTCs harbored BRAF p.V600E. Eight (14%) cases of PPTCs harbored DICER1 mutations with no associated BRAF p.V600E. DICER1 mutations were identified in exons 26 and 27. A novel D1810del (c.5428_5430delGAT) mutation was also detected. We also confirmed the absence of hotspot DICER1 mutations in the matched non-tumor tissue DNA in all 8 DICER1-related PPTCs. The mean age of DICER1-harboring PPTCs was 15.1 (range: 9-18) years whereas the rest of this cohort had a mean age of 14.8 (range 6-18) years. With the exception of one PPTC, all DICER1-related PPTCs were seen in females (female-to-male ratio: 7). The female to male ratio was 3.8 in 48 DICER1-wild type PPTCs. In terms of histological correlates, 5 of 8 (63%) DICER1-mutant PPTCs were invasive encapsulated follicular variant papillary thyroid carcinomas (FVPTCs) including 4 minimally invasive FVPTCs and 1 encapsulated angioinvasive FVPTC, whereas the remaining 3 PPTCs were infiltrative classic papillary thyroid carcinomas (p < 0.05). The incidence of DICER1 mutations was 19.5% in BRAF p.V600E-wild type PPTCs. Sixty-three percent of DICER1 hotspot mutations occurred in invasive encapsulated FVPTCs, and this figure represents 38% of invasive encapsulated FVPTCs. Only one (12%) patient with DICER1-related disease showed a single lymph node with micro-metastasis. Unlike DICER1-wild type patients, no distant metastasis is identified in patients with DICER1-related PPTCs. The current series expands on the surgical epidemiology of somatic DICER1-related PPTCs by correlating the mutation status with the clinicopathological variables. Our findings underscore that female gender predilection and enrichment in low-risk follicular-patterned PTCs are characteristics of DICER1-related PPTCs.

2022 European Thyroid Association Guidelines for the management of pediatric thyroid nodules and differentiated thyroid carcinoma

At present, no European recommendations for the management of pediatric thyroid nodules and differentiated thyroid carcinoma (DTC) exist. Differences in clinical, molecular, and pathological characteristics between pediatric and adult DTC emphasize the need for specific recommendations for the pediatric population. An expert panel was instituted by the executive committee of the European Thyroid Association including an international community of experts from a variety of disciplines including pediatric and adult endocrinology, pathology, endocrine surgery, nuclear medicine, clinical genetics, and oncology. The 2015 American Thyroid Association Pediatric Guideline was used as framework for the present guideline. Areas of discordance were identified, and clinical questions were formulated. The expert panel members discussed the evidence and formulated recommendations based on the latest evidence and expert opinion. Children with a thyroid nodule or DTC require expert care in an experienced center. The present guideline provides guidance for healthcare professionals to make well-considered decisions together with patients and parents regarding diagnosis, treatment, and follow-up of pediatric thyroid nodules and DTC.

An institutional experience with DICER1 mutated thyroid nodules-evaluating the cytomorphology and molecular phenotype

INTRODUCTION

DICER1 mutated thyroid nodules are commonly seen in pediatric populations often, as part of DICER1 syndrome. We seek to evaluate DICER1 mutated thyroid nodules in adult populations to assess whether there exists distinctive clinical, cytologic, histologic, and molecular characteristics that underline our institutional cohort.

MATERIALS AND METHODS

Retrospective analysis was performed on all fine-needle aspiration (FNA) specimens with a corresponding ThyroSeq panel, to select a cohort of cases with DICER1 mutations. Clinical, radiologic, and cytology materials were reviewed, and histology was reviewed for corresponding resection cases were available. ThyroSeq panel was further scrutinized for additional molecular alterations and variant allele frequency.

RESULTS

DICER1 mutated thyroid nodules (n = 8), more commonly occurred in younger adults (P = 0.01) with larger (P = 0.01) nodules and only in female patients in our cohort. FNA commonly demonstrates cellular specimens with banal cytomorphologic cues including regular nuclei, inconspicuous nucleoli, smooth nuclear membranes, and abundant colloid. On retrospective review by 2 cytopathologists, the lesions were frequently diagnosed as Bethesda II (5 of 8) by both reviewers. Histology, when available, showed that all nodules were categorized as follicular adenomas (5 of 5), often demonstrating macrofollicles with papillary excrescences demonstrating bland nuclei (4 of 5). DICER1 mutational profile revealed a variant allele frequency of &gt;40% in 25% of cases (2 of 8) and &gt;30% in an additional 4 cases, highlighting a possible germline association.

CONCLUSIONS

DICER1 mutated nodules may be under-reported due to banal cytomorphologic features and may be associated with an underlying germline alteration.

Ultrasound features of multinodular goiter in DICER1 syndrome

DICER1 syndrome is caused by germline pathogenic mutations in the DICER1 gene. Multinodular goiter (MNG) is a common clinical feature of DICER1 syndrome in children and adults. The aim of this study was to determine the ultrasound (US) characteristics of MNG in patients with DICER1 syndrome. This retrospective study evaluated thyroid US in patients with DICER1 germline mutations (DICER1mut+) performed between 2011 and 2018 at a single center by the same pediatric endocrinologist, and the images were re-examined by an independent pediatric radiologist from another academic center. Patients < 18 years with DICER1mut+ and DICER1mut+ parents without previous thyroidectomy were included. Ultrasound phenotypes of MNG in the setting of DICER1 mutations were compared with known US features of thyroid malignancy. Thirteen DICER1mut+ patients were identified (10 children, 3 adults). Three children had a normal thyroid US; therefore, thyroid abnormalities were assessed in seven children and three adults. In both children and adults, multiple (≥ 3) mixed (cystic/solid) nodules predominated with single cystic, single cystic septated and single solid nodules, occasionally with a “spoke-like” presentation. All solid lesions were isoechogenic, and in only one with multiple solid nodules, intranodular blood flow on power/color Doppler was observed. Remarkably, macrocalcifications were present in all three adults. The spectrum of ultrasonographic findings of MNG in DICER1mut+ patients is characteristic and largely distinct from typical features of thyroid malignancy and therefore should inform physicians performing thyroid US of the possible presence of underlying DICER1 syndrome.

The Multifaceted Profile of Thyroid Disease in the Background of DICER1 Germline and Somatic Mutations: Then, Now and Future Perspectives

DICER1 protein is a member of the ribonuclease (RNAse) III family with a key role in the biogenesis of microRNAs (miRNA) and in microRNA processing, potentially affecting gene regulation at the post-transcriptional level. The role of DICER1 and its relevance to thyroid cellular processes and tumorigenesis have only recently been explored, following the acknowledgement that DICER1 germline and somatic changes can contribute not only to non-toxic multinodule goiter (MNG) lesions detected in individuals of affected families but also to a series of childhood tumours, including thyroid neoplasms, which can be identified from early infancy up until the decade of 40s. In a context of DICER1 germline gene mutation, thyroid lesions have recently been given importance, and they may represent either an index event within a syndromic context or the isolated event that may trigger a deeper and broader genomic analysis screening of individuals and their relatives, thereby preventing the consequences of a late diagnosis of malignancy. Within the syndromic context MNG is typically the most observed lesion. On the other hand, in a DICER1 somatic mutation context, malignant tumours are more common. In this review we describe the role of DICER protein, the genomic events that affect the DICER1 gene and their link to tumorigenesis as well as the frequency and pattern of benign and malignant thyroid lesions and the regulation of DICER1 within the thyroidal environment.

A Japanese Family with DICER1 Syndrome Found in Childhood-Onset Multinodular Goitre

INTRODUCTION

Germline DICER1 mutations have recently been identified in familial multinodular goitre (MNG). The natural history of thyroid nodules in DICER1 carriers in children is unclear. The purpose of this study was to describe the clinical and genetic findings of childhood-onset MNG with DICER1 carrier in a patient who underwent total thyroidectomy.

CASE PRESENTATION

The 6-year-old proband had a thyroid nodule, and the number and size of nodules increased over 3 years. A total thyroidectomy was chosen because of the rapid rise in thyroglobulin levels, discomfort when swallowing, and the mother's history of poorly differentiated thyroid cancer (PDTC). Histopathology revealed adenomatous goitre without malignant cells. Her mother, maternal aunt, and maternal grandmother also had thyroid nodules removed during adolescence. Also, her mother had PDTC with lung metastases, and her maternal aunt had an ovarian germ cell tumour. DICER1 mutation analysis identified a heterozygous novel nonsense mutation (c.4509C>G, p.Y1503X) for the patient, her mother, her maternal grandmother, and her asymptomatic elder brother. Y1503X was identified in all resected thyroid tissues, while heterozygous D1709G, D1810V, and E1813K mutations were identified in individual nodules.

DISCUSSION/CONCLUSION

A thyroid nodule was detected in chemotherapy- or radiotherapy-naïve patient with DICER1 carrier aged 6 years, and MNG developed over 3 years. This pedigree highlights the natural history of nodular disease in DICER1 carriers and identifies a possible association between DICER1 and more aggressive malignancies.

Yield and costs of molecular diagnostics on thyroid cytology slides in the Netherlands, adapting the Bethesda classification

Objective

To evaluate our institutional experience with molecular diagnostics (MD) on thyroid cytology smears, evaluate the costs and describe MD guided clinical management of indeterminate Bethesda III/V thyroid nodules.

Methods

We performed a retrospective review of 164 Bethesda III or V thyroid cytopathology reports subjected to MD from 2013 to 2020, that altered Bethesda classification or management. MD consisted of mutation and gene fusion analysis by next‐generation sequencing (NGS) of morphologically analysed and selected cytological slides. Findings were modelled to nationwide data on Bethesda incidences from ‘the Dutch Pathology Registry’ PALGA, and costs were estimated.

Results

82 of 164 cases received an upgrade in Bethesda class. Twenty cases changed from Bethesda III to IV/V, 62 from Bethesda III or V to VI, and 72 remained unaltered. We estimate net savings with implementing MD, by preventing 454 repeat cytology and 326 (diagnostic) hemithyroidectomies, to be at least 2 million Euro annually in the Netherlands. Per Bethesda III and V patient, net savings would be about 100 Euro and 4100 Euro, respectively.

Conclusion

NGS‐based MD on nucleic acids extracted directly from cytology slides is a feasible and cost saving tool for personalized management in indeterminate Bethesda III/V thyroid cytology. Based on the interpretation of our retrospective data, we assume that this approach results in less disease burden for the patient, reduced surgical interventions and complication risks, reduced sick leave, among others. Further evaluation of structural implementation of the presented approach in routine thyroid Bethesda III/V cytology in a prospective setting is warranted.

Surveillance recommendations for DICER1 pathogenic variant carriers: a report from the SIOPE Host Genome Working Group and CanGene-CanVar Clinical Guideline Working Group

DICER1 syndrome is a rare genetic disorder that predisposes to a wide spectrum of tumors. Developing surveillance protocols for this syndrome is challenging because uncertainty exists about the clinical efficacy of surveillance, and appraisal of potential benefits and harms vary. In addition, there is increasing evidence that germline DICER1 pathogenic variants are associated with lower penetrance for cancer than previously assumed. To address these issues and to harmonize DICER1 syndrome surveillance programs within Europe, the Host Genome Working Group of the European branch of the International Society of Pediatric Oncology (SIOPE HGWG) and Clinical Guideline Working Group of the CanGene-CanVar project in the United Kingdom reviewed current surveillance strategies and evaluated additional relevant literature. Consensus was achieved for a new surveillance protocol and information leaflet that informs patients about potential symptoms of DICER1-associated tumors. The surveillance protocol comprises a minimum program and an extended version for consideration. The key recommendations of the minimum program are: annual clinical examination from birth to age 20 years, six-monthly chest X-ray and renal ultrasound from birth to age 6 years, and thyroid ultrasound every 3 years from age 8 to age 40 years. The surveillance program for consideration comprises additional surveillance procedures, and recommendations for DICER1 pathogenic variant carriers outside the ages of the surveillance interval. Patients have to be supported in choosing the surveillance program that best meets their needs. Prospective evaluation of the efficacy and patient perspectives of proposed surveillance recommendations is required to expand the evidence base for DICER1 surveillance protocols.

Prevalence and Spectrum of DICER1 Mutations in Adult-onset Thyroid Nodules with Indeterminate Cytology

CONTEXT

DICER1 mutations are found in multinodular goiter and differentiated thyroid carcinoma in children, and can be a manifestation of DICER1 syndrome, but the prevalence of DICER1 mutations and their significance in adult-onset thyroid nodules is unknown.

OBJECTIVE

Determine (1) the prevalence of DICER1 hotspot mutations in thyroid nodules; (2) the frequency of a second DICER1 pathogenic variant in thyroid nodules with DICER1 hotspot mutations; (3) the prevalence of other thyroid cancer driver mutations in thyroid nodules with and without DICER1 hotspot mutations.

METHODS

Population-based study of 14 993 consecutive fine needle aspiration biopsies of thyroid nodules evaluated by ThyroSeq v3. From 214 DICER1 hotspot-positive cases, we selected 61, matched to DICER1 hotspot-negative nodules. We performed full sequencing of all exons and exon-intron boundaries of DICER1.

SETTING

Commercial and university-based laboratories in the United States and Canada.

RESULTS

Among 14 993 thyroid nodules, 214 (1.4%) revealed a DICER1 hotspot mutation. A second pathogenic/likely pathogenic variant in DICER1 was found in 45/59 (76%) DICER1 hotspot-positive nodules studied while no other DICER1 variant was identified in the DICER1 hotspot-negative group by full DICER1 sequencing. Other alterations in thyroid-related genes were significantly more frequent in DICER1 hotspot-negative nodules (32/61) than in DICER1 hotspot--positive nodules (4/59) (P < .0001).

CONCLUSION

DICER1 alterations occur in a proportion of adult thyroid nodules and appear mutually exclusive with alterations in other thyroid cancer-related genes. DICER1 hotspot mutations occur with a second hit in most cases and could suggest occult DICER1 syndrome in adults with thyroid nodules.

Prevalence of Pathogenic Germline DICER1 Variants in Young Individuals Thyroidectomised Due to Goitre - A National Danish Cohort

INTRODUCTION

DICER1 syndrome encompasses a variety of benign and malignant manifestations including multinodular goitre, which is the most common manifestation among individuals carrying pathogenic DICER1 variants. This is the first study estimating the prevalence of pathogenic DICER1 variants in young individuals with multinodular goitre.

METHODS

Danish individuals diagnosed with nodular goitre based on thyroidectomy samples in 2001-2016 with the age limit at time of operation being ≤ 25 years were offered germline DICER1 gene testing.

RESULTS

Six of 46 individuals, 13% (CI [3.3;22.7], p <0.05), diagnosed with nodular goitre on the basis of thyroidectomy samples under the age of 25 years had pathogenic germline variants in DICER1. They were found in different pathoanatomical nodular goitre cohorts i.e. nodular goitre (n=2), colloid nodular goitre (n=3) and hyperplastic nodular goitre (n=1).

CONCLUSIONS

We recommend referral of patients thyroidectomised due to goitre aged <21 years and patients thyroidectomised due to goitre aged <25 years with a family history of goitre to genetic counselling. Patients of all ages thyroidectomised due to goitre, who are affected by another DICER1 manifestation should be referred to genetic counselling.

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.

Poorly differentiated thyroid carcinoma of childhood and adolescence: a distinct entity characterized by DICER1 mutations

Poorly differentiated thyroid carcinomas (PDTC) in young individuals are rare and their clinical and histopathologic features, genetic mechanisms, and outcomes remain largely unknown. Here, we report a detailed characterization of a series of six PDTC in patients ≤21 years old defined by Turin diagnostic criteria studied for mutations and gene fusions characteristic of thyroid cancer using targeted next-generation sequencing (NGS) and whole-exome sequencing (WES). All tumors had solid, insular, or trabecular growth pattern and high mitotic rate, and five out of six tumors showed tumor necrosis. Targeted NGS assay identified somatic mutations in the DICER1 gene in five of six (83%) tumors, all of which were "hotspot" mutations encoding the metal-ion binding sites of the RNase IIIb domain of DICER1. WES was performed in five cases which confirmed all hotspot mutations and detected two tumors with additional inactivating DICER1 alterations. Of these two, one was a germline pathogenic DICER1 variant and the other had loss of heterozygosity for DICER1. No other mutations or gene fusions characteristic of adult well-differentiated thyroid cancer and PDTC (BRAF, RAS, TERT, RET/PTC, and other) were detected. On follow-up, available for five patients, three patients died of disease 8-24 months after diagnosis, whereas two were alive with no disease. The results of our study demonstrate that childhood- and adolescent-onset PDTC are genetically distinct from adult-onset PDTC in that they are strongly associated with DICER1 mutations and may herald DICER1 syndrome in a minority. As such, all young persons with PDTC may benefit from genetic counseling. Furthermore, their clinically aggressive behavior contrasts sharply with the indolent nature of the great majority of thyroid tumors with DICER1 mutations reported to date.

An update on the central nervous system manifestations of DICER1 syndrome

DICER1 syndrome is a rare tumor predisposition syndrome with manifestations that predominantly affect children and young adults. The syndrome is typically caused by heterozygous germline loss-of-function DICER1 alterations accompanied on the other allele by somatic missense mutations occurring at one of a few mutation hotspots within the sequence encoding the RNase IIIb domain. DICER1 encodes a member of the microRNA biogenesis machinery. The syndrome spectrum is highly pleiotropic and features a unique constellation of benign and malignant neoplastic and dysplastic lesions. Pleuropulmonary blastoma (PPB), the most common primary lung cancer in children, is the hallmark tumor of the syndrome. Other manifestations include ovarian Sertoli-Leydig cell tumor, cystic nephroma arising in childhood, multinodular goiter, thyroid carcinoma, anaplastic sarcoma of the kidney, embryonal rhabdomyosarcoma, and nasal chondromesenchymal hamartoma, in addition to other rare entities. Several central nervous system (CNS) manifestations have also been defined, including metastases of PPB to the cerebrum, pituitary blastoma, pineoblastoma, ciliary body medulloepithelioma, and most recently primary DICER1-associated CNS sarcomas and ETMR-like infantile cerebellar embryonal tumor. Macrocephaly is a recently reported non-neoplastic, haploinsufficient phenotype. In this manuscript, we review the CNS manifestations of DICER1 syndrome.

Multinodular goitre is a gateway for molecular testing of DICER1 syndrome

BACKGROUND

DICER1 syndrome is an autosomal dominant disorder that predisposes individuals to develop benign or malignant tumours from infancy to adulthood. There is low-to-moderate penetrance of tumour development, which is sex- and age-dependent. Multinodular goitre (MNG) is among the most highly penetrant phenotype of the disorder, especially in females.

PATIENTS AND METHODS

We report a series of eight families referred for childhood-onset of MNG or DICER1-related tumours with familial history of MNG in relatives. No additional families with these criteria stated were identified during the same date. We screened DNA samples from the probands and members of their family (40) for constitutional DICER1 variants using Next Generation Sequencing tools.

RESULTS

Germline pathogenic DICER1 gene variants were identified in all probands and several of their relatives: 64% presented with MNG/thyroidectomy as the phenotypic expression of the syndrome. DICER1 gene variants were identified in the RNAseIII and the PAZ domains. All tumour tissues studied presented clonal pathogenic variants in hotspot regions. Early identification of DICER1 variant carriers has permitted diagnosis and therapeutic scheme correction for two patients and cascade testing in relatives.

CONCLUSIONS

Multinodular goitre is uncommon in children. Childhood-onset MNG, multiple occurrences of the disease within the same family, or its association with rare benign or malignant tumours should raise suspicions of anomalies in the DICER1 gene, as proposed by recent international recommendations. Early detection of DICER1 pathogenic variants has important consequences in terms of therapeutic strategy, early tumour screening, and genetic counselling.