DICER1 Mutations Research Articles

Prevalence and Spectrum of DICER1Mutations in Adult-Onset Thyroid Nodules

Abstract 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. Design: 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<0.0001). Conclusions: 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.

Identification of a Novel DICER1 Germline Mutation in Thyroid Follicular Adenoma Using Whole Exome Sequencing

Backgrounds: DICER1 protein is a member of the ribonuclease III family of proteins that cleaves non-coding small RNA precursors to generate mature miRNAs, which in turn regulate gene expression post-transcriptionally. Thyroid abnormalities are frequently observed in DICER1 syndrome with multinodular goiter present in families in which a germline DICER1 mutation is segregating. Recently, we identified a germline DICER1 mutation in a family with multiple tumors using whole exome sequencing (WES). Methods and Materials: Following informed consent, WES of peripheral blood DNA was carried out on affected individual. Sanger sequencing was performed to confirm the DICER1 variant detected by WES and to assess her family for mutation in the same DICER1 exon (exon 20). Results: An 8 year-old girl presented with abdominal mass. Laparoscopic radical nephrectomy was done due to Wilms tumor. At age 12, palpable mass on the right thyroid lobe was found, and right hemithyroidectomy was performed. She was diagnosed with follicular adenoma, and she started to take levothyroxine. At age 13, palpable thyroid mass on the left thyroid lobe was identified, and total thyroidectomy was performed due to progressively enlarged remnant thyroid gland with multiple nodules. The pathological result was adenomatous goiter with a cystic change. During the evaluation, a 1.5cm follicular cyst in the left ovary, 0.7cm cystic lesion in the right middle lobe of the lung, and air-trappings in both lungs were observed. We performed WES which revealed a novel heterozygous missense mutation, c.3506C>G(p.S1169*) in exon 20 of the DICER1 gene. During the follow-up, she showed a severely enlarged right kidney with multiple septated cysts. Right total nephrectomy was done due to hemorrhage progression in cysts and biopsy revealed cystic nephroma. Continuous renal replacement therapy was applied after right nephrectomy, and maintenance hemodialysis was applied. Conclusions: We identified a novel DICER1 germline mutation in a family with thyroid follicular adenoma, Wilms tumor, and contralateral progressive cystic nephroma which is the first report in Korea.

Spectrum of DICER1 Germline Pathogenic Variants in Ovarian Sertoli-Leydig Cell Tumor.

Sertoli–Leydig Cell Tumors (SLCTs) are rare ovarian sex cord-stromal neoplasms, which predominantly affect adolescents and young female adults. The SLCTs clinical diagnosis and treatment remains challenging due to the rarity and the varied presentation. A large majority of SLCTs are unilateral, but also bilateral neoplasms have been reported, sometimes in the context of DICER1 syndrome. In fact, the most significant discovery regarding the molecular genetics basis of SLCTs was the finding of somatic and germline pathogenic variants in the DICER1 gene. The DICER1 protein is a key component of the micro-RNA processing pathway. Germline DICER1 pathogenic variants are typically inherited in an autosomal dominant pattern and are most often loss-of-function variants dispersed along the length of the gene. Contrarily, DICER1-related tumors harbor a characteristic missense “RNase IIIb hotspot” mutation occurring in trans, or, less frequently, loss of heterozygosity (LOH) event involving the wild-type allele. While DICER1 mutations have been identified in approximately 60% of SLCTs, especially in the moderately or poorly differentiated types, there are only a few case reports of ovarian SLCT with underlying germline DICER1 mutations. In this review, we focus on the molecular genetic features of SLCT, performing an extensive survey of all germline pathogenic variants modifying the whole sequence of the DICER1 gene. We point out that DICER1 genetic testing, coupled with an accurate variants classification and timely counseling, is of crucial importance in the clinical management of ovarian SLCT-affected patients.

Clinicopathologic and molecular analysis of embryonal rhabdomyosarcoma of the genitourinary tract: evidence for a distinct DICER1-associated subgroup

Embryonal rhabdomyosarcoma (ERMS) of the uterus has recently been shown to frequently harbor DICER1 mutations. Interestingly, only rare cases of extrauterine DICER1-associated ERMS, mostly located in the genitourinary tract, have been reported to date. Our goal was to study clinicopathologic and molecular profiles of DICER1-mutant (DICER1-mut) and DICER1-wild type (DICER1-wt) ERMS in a cohort of genitourinary tumors. We collected a cohort of 17 ERMS including nine uterine (four uterine corpus and five cervix), one vaginal, and seven urinary tract tumors. DNA sequencing revealed mutations of DICER1 in 9/9 uterine ERMS. All other ERMS of our cohort were DICER1-wt. The median age at diagnosis of patients with DICER1-mut and DICER1-wt ERMS was 36 years and 5 years, respectively. Limited follow-up data (available for 15/17 patients) suggested that DICER1-mut ERMS might show a less aggressive clinical course than DICER1-wt ERMS. Histological features only observed in DICER1-mut ERMS were cartilaginous nodules (6/9 DICER1-mut ERMS), in one case accompanied by foci of ossification. Recurrent mutations identified in both DICER1-mut and DICER1-wt ERMS affected KRAS, NRAS, and TP53. Copy number analysis revealed similar structural variations with frequent gains on chromosomes 2, 3, and 8, independent of DICER1 mutation status. Unsupervised hierarchical clustering of array-based whole-genome DNA methylation data of our study cohort together with an extended methylation data set including different RMS subtypes from genitourinary and extra-genitourinary locations (n = 102), revealed a distinct cluster for DICER1-mut ERMS. Such tumors clearly segregated from the clusters of DICER1-wt ERMS, alveolar RMS, and MYOD1-mutant spindle cell and sclerosing RMS. Only one tumor, previously diagnosed as ERMS arising in the maxilla of a 6-year-old boy clustered with DICER1-mut ERMS of the uterus. Subsequent sequencing analysis identified two DICER1 mutations in the latter case. Our results suggest that DICER1-mut ERMS might qualify as a distinct subtype in future classifications of RMS.

Pleuropulmonary blastoma in children and adolescents: The EXPeRT/PARTNER diagnostic and therapeutic recommendations.

Pleuropulmonary blastoma (PPB) is a rare cancer occurring mainly during early childhood and often associated with germline DICER1 mutations. It is classified by the macroscopic appearance into three interrelated clinico-pathologic entities on a developmental continuum. Complete tumor resection is a main prognostic factor and can be performed at diagnosis or after neoadjuvant treatment that includes chemotherapy and in some cases radiotherapy. Optimal modalities of neo- or adjuvant treatments can be challenging taking into account potential long-term toxicities in this young population. This paper presents the recommendations for diagnosis and treatment of children and adolescents with PPB elaborated by the European Cooperative Study Group for Pediatric Rare Tumors (EXPeRT) within the European Union-funded project PARTNER (Paediatric Rare Tumours Network - European Registry).

Pleuropulmonary Blastoma in Pediatric Lung Lesions.

Pediatric lung lesions are a group of mostly benign pulmonary anomalies with a broad spectrum of clinical disease and histopathology. Our objective was to evaluate the characteristics of children undergoing resection of a primary lung lesion and to identify preoperative risk factors for malignancy. A retrospective cohort study was conducted by using an operative database of 521 primary lung lesions managed at 11 children's hospitals in the United States. Multivariable logistic regression was used to examine the relationship between preoperative characteristics and risk of malignancy, including pleuropulmonary blastoma (PPB). None of the 344 prenatally diagnosed lesions had malignant pathology (P < .0001). Among 177 children without a history of prenatal detection, 15 (8.7%) were classified as having a malignant tumor (type 1 PPB, n = 11; other PPB, n = 3; adenocarcinoma, n = 1) at a median age of 20.7 months (interquartile range, 7.9-58.1). Malignancy was associated with the DICER1 mutation in 8 (57%) PPB cases. No malignant lesion had a systemic feeding vessel (P = .0427). The sensitivity of preoperative chest computed tomography (CT) for detecting malignant pathology was 33.3% (95% confidence interval [CI]: 15.2-58.3). Multivariable logistic regression revealed that increased suspicion of malignancy by CT and bilateral disease were significant predictors of malignant pathology (odds ratios of 42.15 [95% CI, 7.43-340.3; P < .0001] and 42.03 [95% CI, 3.51-995.6; P = .0041], respectively). In pediatric lung masses initially diagnosed after birth, the risk of PPB approached 10%. These results strongly caution against routine nonoperative management in this patient population. DICER1 testing may be helpful given the poor sensitivity of CT for identifying malignant pathology.

Pleuropulmonary blastoma: A single-center case series of seven patients

Introduction: Pleuropulmonary blastoma (PPB) is a rare and aggressive primary neoplasm of pleuropulmonary mesenchyme occurring in children. The International PPB Registry was established in 1988 to collect and assess data on PPB worldwide. Objectives: The objectives of the study were to assess the clinical characteristics, histopathology, genetic studies, management, and treatment outcomes of patients with PPB in our institution, and to compare with the published literature. Materials and Methods: We retrospectively reviewed the medical records of all PPB cases diagnosed at Princess Margaret Hospital for Children in West Australia over a period of 26 years (1990–2016). Their clinical characteristics, histopathology, genetic studies, management, and treatment outcomes were recorded. Results: Seven children (four boys and three girls) were treated for PPB at a mean age of 11.5 months (ranges 1 month–3.55 years). Histopathology showed type I PPB in five, type II in one, and type III in one. All seven patients underwent thoracotomy/lobectomy of the corresponding site. One patient required additional bladder resection for coexisting rhabdomyosarcoma. One patient was found to be positive for DICER1 gene mutation. Six patients received adjuvant chemotherapy with vincristine, Adriamycin, and cyclophosphamide regime, with the mean duration of treatment for five patients being 9.4 months excluding one patient who deceased without completion of chemotherapy. During a mean follow-up time of 9 years, the overall survival rate for this cohort was 85.7% (6/7). Conclusion: Our results are comparable to those reported in the literature. It is crucial for clinicians to consider PPB in the evaluation of patients presenting with a cystic lung abnormality, especially in cases with DICER1 mutation or a strong family history of unusual cancers

High mutation burden in the checkpoint and micro-RNA processing genes in myelodysplastic syndrome.

A number of sequencing studies identified the prognostic impact of somatic mutations in myelodysplastic syndrome (MDS). However the majority of them focused on methylation regulation, apoptosis and proliferation genes. Despite the number of experimental studies published on the role of micro-RNA processing and checkpoint genes in the development of MDS, the clinical data about mutational landscape in these genes is limited. We performed a pilot study which evaluated mutational burden in these genes and their association with common MDS mutations. High prevalence of mutations was observed in the genes studied: 54% had mutations in DICER1, 46% had mutations in LAG3, 20% in CTLA4, 23% in B7-H3, 17% in DROSHA, 14% in PD-1 and 3% in PD-1L. Cluster analysis that included these mutations along with mutations in ASXL1, DNMT3A, EZH2, IDH1, RUNX1, SF3B1, SRSF2, TET2 and TP53 effectively predicted overall survival in the study group (HR 4.2, 95%CI 1.3–13.6, p = 0.016). The study results create the rational for incorporating micro-RNA processing and checkpoint genes in the sequencing panels for MDS and evaluate their role in the multicenter studies.

Race disparities in genetic alterations within Wilms tumor specimens

BackgroundWilms tumor (WT) affects Black children disproportionately. Genetic aberrations within WT specimens that contribute to this disparity have not been reported. MethodsThe Therapeutically Applied Research to Generate Effective Treatments (TARGET) database was queried for WT patient and genomic features. Clinical and genetic variables were compared by race. ResultsWithin the discovery set (enriched for adverse events; N = 94 White, 19 Black, 14 Other/unreported patients), Black children were more likely to present with advanced stage disease (p = 0.019). Within the validation set (primarily a random sampling of NWTS-5; N = 360 White, 92 Black, 72 Other/Unreported), Black children appeared older at diagnosis (p = 0.050), had decreased median follow-up time (p<0.0005) and were over-represented (17.4%) relative to the concurrent U.S. Census (12.8%). Among the 37 target genes sequenced, ACTB (p = 0.030) and DICER1 (p = 0.026) mutations were more common in Black patient specimens, whereas DGCR8 (p = 0.041) mutations were more common in White patient specimens. White patient specimens were more likely to contain one or multiple targeted mutations (p = 0.026). ConclusionWithin the TARGET database, Black children were over-represented and harbored WT specimens containing more frequent ACTB and DICER1 mutations. In contrast, WT from White children contained overall more mutations in targeted genes and specifically in DGCR8. Level of EvidenceIII.

Pleuropulmonary Blastoma with Hotspot Mutations in RNase IIIb Domain of DICER 1: Clinicopathologic Study of 10 Cases in a Single-Institute Experience

Introduction: Pleuropulmonary blastoma (PPB) is a rare sarcomatous malignancy involving the lung and pleura which occurs in early childhood. Cystic PPB in the early stage can be misdiagnosed as other cystic diseases. Early detection of this entity is important for appropriate treatment and prevention of disease progression. Hotspot mutations in the ribonuclease IIIb (RNase IIIb) domain of DICER1 have been reported to have a crucial role as genetic factors of PPB and DICER1 familial syndrome. We reviewed the clinicopathologic findings of PPB and the status of DICER1 hotspot mutation and patients’ clinical course. Methods: We retrospectively reviewed all patients with histologically confirmed PPB at Asan Medical Center between 2000 and 2017. Ten cases were identified in the database, and their clinicopathologic parameters were evaluated. PPB was classified into the following 3 pathologic subtypes: type I (purely cystic), type II (mixed cystic and solid), and type III (entirely solid). The status of DICER1 mutation in 2 hotspot regions of the RNase IIIb domain was evaluated by Sanger sequencing. Results: The most frequent PPB type was II (6 cases), followed by I and III (2 cases each). The age at diagnosis ranged from 16 months to 15 years. All patients underwent surgery, and all patients received adjuvant or neoadjuvant chemotherapy. Four of 7 patients had missense mutations in the RNase IIIb hotspot; the base and predicted corresponding amino acid changes were c.5113 G>A (p.E1705K), c.5407 G>A (p.E1803K), c.5425 G>A (p.G1809R), and c.5428 G>T (p.D1810Y). There was no particular association between the presence of the hotspot mutation and histologic type. Nine patients survived with no evidence of disease for a median interval of 93 (range, 13–199) months. Only 1 patient diagnosed with type III PPB at the age of 18 years had recurrence after 20.8 months and eventually died 66 months after the initial diagnosis. Conclusions: Late detection of solid PPB is associated with poor prognosis. Considering the rarity of PPB disease and the importance of DICER1 hotspot mutation in pathogenesis, DICER1 hotspot mutation testing and identification in the early cystic stage can improve patient outcomes.

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

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

Genomics and Epigenomics of Pituitary Tumors: What Do Pathologists Need to Know?

Molecular pathology has advanced our understanding of many tumors and offers opportunities to identify novel therapies. In the pituitary, the field has uncovered several genetic mutations that predispose to pituitary neuroendocrine tumor (PitNET) development, including MEN1, CDKN1B, PRKRIα, AIP, GPR101, and other more rare events; however, these genes are only rarely mutated in sporadic PitNETs. Recurrent genetic events in sporadic PitNETs include GNAS mutations in a subset of somatotroph tumors and ubiquitin-specific peptidase mutations (e.g., USP8, USP48) in some corticotroph tumors; to date, neither of these has resulted in altered management, and instead, the prognosis and management of PitNETs still rely more on cell type and subtype as well as local growth that determines surgical resectability. In contrast, craniopharyngiomas have either CTNNB1 or BRAFV600E mutations that correlate with adamantinomatous or papillary morphology, respectively; the latter offers the opportunity for targeted therapy. DICER1 mutations are found in patients with pituitary blastoma. Epigenetic changes are implicated in the pathogenesis of the more common sporadic pituitary neoplasms including the majority of PitNETs and tumors of pituicytes.

A pan-cancer atlas of somatic mutations in miRNA biogenesis genes.

It is a well-known and intensively studied phenomenon that the levels of many miRNAs are differentiated in cancer. miRNA biogenesis and functional expression are complex processes orchestrated by many proteins cumulatively called miRNA biogenesis proteins. To characterize cancer somatic mutations in the miRNA biogenesis genes and investigate their potential impact on the levels of miRNAs, we analyzed whole-exome sequencing datasets of over 10 000 cancer/normal sample pairs deposited within the TCGA repository. We identified and characterized over 3600 somatic mutations in 29 miRNA biogenesis genes and showed that some of the genes are overmutated in specific cancers and/or have recurrent hotspot mutations (e.g. SMAD4 in PAAD, COAD and READ; DICER1 in UCEC; PRKRA in OV and LIN28B in SKCM). We identified a list of miRNAs whose level is affected by particular types of mutations in either SMAD4, SMAD2 or DICER1 and showed that hotspot mutations in the RNase domains in DICER1 not only decrease the level of 5p-miRNAs but also increase the level of 3p-miRNAs, including many well-known cancer-related miRNAs. We also showed an association of the mutations with patient survival. Eventually, we created an atlas/compendium of miRNA biogenesis alterations providing a useful resource for different aspects of biomedical research.

Endometrial Stem/Progenitor cell (ES/PC) Marker Expression Profile in Adenosarcoma and Endometrial Stromal Sarcoma

BackgroundThe uterus is one of the most dynamic organs in the human body, and this dynamic homeostasis is supported by endometrial stem/progenitor cells (ES/PCs), which are heterogeneous in their phenotype and degree of differentiation. ES/PCs are generally localized in the endometrial stroma, the site of origin for adenosarcoma and endometrial stromal sarcoma (ESS). Subsets of ESSs and adenosarcomas harbor SUZ12 or DICER1 gene alterations, two genes with roles in embryonic stem cell biology. However, the possible contribution of ES/PCs to tumorigenesis is unexplored. MethodWe examined the expression of eleven ES/PC markers, along with three proteins expressed in the mature endometrial stroma (ER, PR and CD10) in 60 uterine tumors (24 low-, 11 high-grade ESS, 25 adenosarcomas). Protein expression profiles were assessed by unsupervised hierarchical clustering. miRNA expression profiles were examined in a subset of adenosarcoma with/without DICER1 mutations, using the NanoString platform. ResultsES/PC markers were variably expressed, and the tumors exhibited limited immunophenotypic resemblance to different ES/PCs. Within the ESSs, the ES/PC marker clustering pattern was prognostic for both overall and disease-free survival. Comparing adenosarcomas and ESSs, most high-grade ESSs clustered with one another, while low-grade ESSs and adenosarcomas tended to cluster with one another. Among the adenosarcomas, the miRNA expression profiles were varied with respect to the DICER1 mutation status, with pathway analysis pointing to dysregulated signal transduction and stem cell biology. ConclusionsESSs and adenosarcomas exhibit varying immunophenotypic resemblance to ES/PCs. These expression profiles have prognostic implications and may be genetically driven.

Gene of the month: DICER1: ruler and controller

DICER1 is a highly conserved RNaseIII endoribonuclease that has a critical role in the biogenesis of microRNAs (miRNAs). miRNAs are small regulatory RNAs responsible for post-transcriptional gene silencing, controlling more...

RARE-43. FAVORABLE OUTCOME OF A YOUNG GIRL WITH RECURRENT METASTATIC PINEOBLASTOMA ASSOCIATED WITH A DICER1 MUTATION

Pineoblastomas have been thought to portend a poor prognosis, especially in younger children or those with metastases. Long term survivors after relapse, especially for those with metastatic disease are rare. We report a young girl with a DICER1 mutation who survived recurrent metastatic pineoblastoma. She was initially diagnosed at the age of 3 with a localized pineoblastoma, underwent gross total surgical resection, and received high dose chemotherapy with autologous stem cell transplant per COG ACNS0334 without radiation therapy. 16 months after completion of treatment, she relapsed at primary site with widespread spinal metastasis. She then received cranial spinal radiation of 3600Gy with proton beam, with boost to primary to 5580Gy, followed by chemotherapy with Temozolomide, Irinotecan and Avastin per COG ACNS0821. She is now 3 years and 3 months from completion of treatment, is doing well clinically with stable imaging findings. No particular alteration was identified from the tumor molecular testing of her initial pineoblastoma. Of note, she was diagnosed with pleuropulmonary blastoma soon after her initial diagnosis of pineoblastoma, and was found to have a DICER1 mutation (c.2062C>T; pR688*) thought to be a nonsense mutation. While radiation therapy following recurrence is known to improve the outcome, more recent studies suggest that tumors lacking the molecular features of high grade glioma also has a positive impact on prognosis. In addition, we speculate that DICER1 mutations might increase sensitivity of cancer cells to some chemotherapy through modulating gene expression and /or interfering with DNA repair mechanisms, therefore, affecting treatment outcome.

RARE-42. PRIMARY INTRACRANIAL SARCOMA WITH DICER1-MUTATION - TREATMENT RESULTS OF A NEW MOLECULAR ENTITY

OBJECTIVEAn unexpectedly high incidence of sarcomas of the Central Nervous System (SCNS) was recently observed in Peru. We describe clinical and biological characteristics of the disease.METHODSSeventy pediatric patients with primary SCNS diagnosed between January 2005 and June 2018 were analyzed. DNA methylation profiling and gene panel sequencing was available from 28 and 27 tumors, respectively.RESULTSMedian age was 6 years (range 2–17.5), 66/70 patients had supratentorial tumors, 56 patients intratumoral hemorrhage at diagnosis. Three patients fulfilled clinical criteria of NF1; 35 had café-au-lait spots and/or freckling. DNA-methylation profiling classified 28/28 as “intracranial spindle cell sarcoma with rhabdomyosarcoma-like features and DICER1 mutations”. DICER1 mutations were found in 26/27, TP53 mutations in 22/27, and RAS-pathway gene mutations (NF1, KRAS, NRAS) in 19/27 tumors, all of which were somatic (germline control available in n=19 cases). Survival was analyzed in 57 patients with non-metastatic disease who received adjuvant therapy. Two patients had metastatic disease, eleven did not receive or abandoned treatment. Two-year OS was 66.3% (95%-CI: 54–81%), 2-year PFS 51% (38–67%). PFS was highest in patients treated with postoperative ICE chemotherapy followed by radiotherapy and ICE (2y-EFS 79% [59–100%], n=18) and worse after upfront radiotherapy followed by ICE (40% [19–85%]; n=10) or VAC (50% [28–88%], n=12) and radiotherapy only (21% [6–71%], n=11; p=0.008).CONCLUSIONPrimary SCNS with DICER1 mutation have an aggressive clinical course. A combination of chemotherapy and radiotherapy seems beneficial. A link to a cancer predisposition syndrome could not be established so far.

RARE-22. GERMLINE PATHOGENIC VARIANT c.1552G&amp;gt;A;p.E518K IN DGCR8 CONFERS SUSCEPTIBILITY FOR SCHWANNOMATOSIS AND THYROID TUMORS

Germline mutations in DICER1 cause a pleiotropic susceptibility syndrome characterized by the development of pediatric or early-onset tumors including pleuropulmonary blastoma, Wilms tumors, pineoblastomas, multinodular goiter (MNG) and thyroid cancers. Somatic mutations in the other two microprocessors DROSHA and DGCR8 have been found in Wilms Tumors and pineoblastomas. We present here two families with peripheral schwannomatosis and thyroid tumors carrying a germline variant c.1552G>A;p.E518K in DGCR8. Family one had six affected members with early-onset MNG and five of them developed schwannomatosis. All five members were heterozygous for the variant. One of the carriers had also been diagnosed with a choroid plexus papilloma at 7 years old. The common second event in all tumors tested was the loss of chromosome 22 at the somatic level. In family two, a 35-year-old male was diagnosed with a peripheral schwannoma at the age of 12. Since then, he has developed seven extra peripheral schwannomas (one of which was an ancient schwannoma) and papillary thyroid cancer. DGCR8 lies on chromosome 22q, adjacent to the three schwannoma genes: LZTR1, SMARCB1 and NF2. The variant, c.1552G>A;p.E518K localizes to the first RNA-binding domain of DGCR8 and structural modelling predicts that it abolishes proper binding of RNA. It is also a hotspot somatic mutation in Wilms tumors. Using miRNA profiling, we show that this variant disrupts global microRNA production and DGCR8 mutated tumors show a specific miRNA profile different from DGCR8 wild type tumors. These findings reinforce DGCR8 as a novel susceptibility gene for schwannomatosis and thyroid tumors.

RARE-53. PINEAL PARENCHYMAL TUMOR OF INTERMEDIATE DIFFERENTIATION (PPTID) AND DICER1 SYNDROME: A CASE REPORT

BACKGROUNDDICER1 syndrome is a rare inherited tumor predisposition syndrome linked to an increased risk of several malignancies. Affected individuals most commonly develop pleuropulmonary blastoma (PPB) and ovarian sex cord-stromal tumors. Brain tumors in these patients are rare, however; the increased frequency of pineoblastoma in this population has been established. Traditionally, pineal parenchymal tumors of intermediate differentiation (PPTIDs) have not been associated with DICER1 syndrome, with research suggesting alternative mutations driving tumorigenesis. These tumors are pathologically and clinically diverse, with long-term surveillance based on therapeutic interventions. Here we describe a case of a germline DICER1 mutation in a patient with a PPTID, suggesting that this mutation is not limited to pineoblastoma as previously reported. CASE: We describe a 19 year-old female with a WHO grade III PPTID treated with multimodal therapy including surgery, craniospinal irradiation (CSI) and chemotherapy. She was noted to have a thyroid mass at diagnosis and was subsequently diagnosed with a benign thyroid nodule, followed most recently by a cataract with pathology concerning for medulloepithelioma of the ciliary body. Due to the known association between medulloepithelioma and DICER1 syndrome, targeted germline sequencing was obtained and confirmed a pathogenic heterozygous mutation.CONCLUSIONTo our knowledge this is the first report of a PPTID in a patient with DICER1 syndrome. This association highlights the clinical implications of molecular evaluation in pediatric brain tumors, for both immediate therapeutic decisions and long-term surveillance.

Deletion of Yy1 in mouse lung epithelium unveils molecular mechanisms governing pleuropulmonary blastoma pathogenesis.

ABSTRACTPleuropulmonary blastoma (PPB) is a very rare pediatric lung disease. It can progress from abnormal epithelial cysts to an aggressive sarcoma with poor survival. PPB is difficult to diagnose as it can be confounded with other cystic lung disorders, such as congenital pulmonary airway malformation (CPAM). PPB is associated with mutations in DICER1 that perturb the microRNA (miRNA) profile in lung. How DICER1 and miRNAs act during PPB pathogenesis remains unsolved. Lung epithelial deletion of the Yin Yang1 (Yy1) gene in mice causes a phenotype mimicking the cystic form of PPB and affects the expression of key regulators of lung development. Similar changes in expression were observed in PPB but not in CPAM lung biopsies, revealing a distinctive PPB molecular signature. Deregulation of molecules promoting epithelial–mesenchymal transition (EMT) was detected in PPB specimens, suggesting that EMT might participate in tumor progression. Changes in miRNA expression also occurred in PPB lung biopsies. miR-125a-3p, a candidate to regulate YY1 expression and lung branching, was abnormally highly expressed in PPB samples. Together, these findings support the concept that reduced expression of YY1, due to the abnormal miRNA profile resulting from DICER1 mutations, contributes to PPB development via its impact on the expression of key lung developmental genes.This article has an associated First Person interview with the joint first authors of the paper.