Germline DICER1 Research Articles

Molecular subgrouping of primary pineal parenchymal tumors reveals distinct subtypes correlated with clinical parameters and genetic alterations.

Tumors of the pineal region comprise several different entities with distinct clinical and histopathological features. Whereas some entities predominantly affect adults, pineoblastoma (PB) constitutes a highly aggressive malignancy of childhood with a poor outcome. PBs mainly arise sporadically, but may also occur in the context of cancer predisposition syndromes including DICER1 and RB1 germline mutation. With this study, we investigate clinico-pathological subgroups of pineal tumors and further characterize their biological features. We performed genome-wide DNA methylation analysis in 195 tumors of the pineal region and 20 normal pineal gland controls. Copy-number profiles were obtained from DNA methylation data; gene panel sequencing was added for 93 tumors and analysis was further complemented by miRNA sequencing for 22 tumor samples. Unsupervised clustering based on DNA methylation profiling separated known subgroups, like pineocytoma, pineal parenchymal tumor of intermediate differentiation, papillary tumor of the pineal region and PB, and further distinct subtypes within these groups, including three subtypes within the core PB subgroup. The novel molecular subgroup Pin-RB includes cases of trilateral retinoblastoma as well as sporadic pineal tumors with RB1 alterations, and displays similarities with retinoblastoma. Distinct clinical associations discriminate the second novel molecular subgroup PB-MYC from other PB cases. Alterations within the miRNA processing pathway (affecting DROSHA, DGCR8 or DICER1) are found in about two thirds of cases in the three core PB subtypes. Methylation profiling revealed biologically distinct groups of pineal tumors with specific clinical and molecular features. Our findings provide a foundation for further clinical as well as molecular and functional characterization of PB and other pineal tumors, including the role of miRNA processing defects in oncogenesis.

PDTM-24. PINEOBLASTOMA SEGREGATES INTO MOLECULAR SUBTYPES WITH DISTINCT CLINICOPATHOLOGIC FEATURES: REPORT FROM THE RARE BRAIN TUMOUR CONSORTIUM

Abstract BACKGROUND Pineoblastoma (PB) is a rare but aggressive pediatric brain tumour arising from the pineal gland. Overall survival rates are estimated at 50–70%, with younger patients (< 5 years old) faring much worse (15–40%) despite intensive treatment regimens. Although germline RB1 and DICER1 alterations have been reported in a small proportion of PB, the clinical significance of such alterations and the biology of sporadic cases remains unknown. METHODS We collected tumor tissue from 93 PB cases diagnosed at their referring centres. We undertook global DNA methylation profiling and performed multiple orthogonal consensus clustering analyses to elucidate PB subgroups. Chromosomal copy number alterations were determined using Conumee and GISTIC2, and whole exome or targeted sequencing was completed. Clinical data was analyzed with correlative statistical methods and outcomes were measured by Kaplan-Meier survival estimates. RESULTS PB comprise five epigenetic groups, designated 1, 2, 3, 4A, and 4B. Deleterious, mutually exclusive alterations affecting miRNA biogenesis pathway members (DICER1, DROSHA, and DGCR8) were observed in 12/21 group 1 and 11/11 group 2 samples. Group 4A was characterized by recurrent RB1 loss and gain of the oncogenic miR-17/92, and group 4B by recurrent gain or amplification of MYC. These groups also exhibit distinct clinical features. PB groups 1–3 arose in older children (median ages 5.2–14.0 years) and had intermediate to excellent outcome (5-year OS of 71.9–100%). Group 4A and 4B were restricted to much younger children (median age 1.3–1.4 years) and had dismal prognoses (5-year OS 37.5% and 28.6%, respectively). CONCLUSIONS PB divides into five groups with distinct genetic and clinical profiles. These findings will have important implications for precise patient stratification and form the foundation for preclinical studies of biology-informed therapies.

Genetic Causes of Rare Pediatric Ovarian Tumors.

Ovarian tumors in childhood and adolescence are distinguished from those that arise in adulthood by their histological subtype. These tumors may arise as the first manifestation of a cancer predisposition syndrome. Correct diagnosis of the syndrome may offer the possibility of surveillance for other members of the patients family. To summarize current knowledge about paediatric ovarian tumors that may be associated with genetically defined cancer syndromes. Juvenile granulosa cell tumors occur in those with Ollier disease and Maffucci syndrome; they are caused by postzygotic IDH1 and IDH2 gene mutations. Sertoli-Leydig cell tumors usually arise in association with DICER1 syndrome, which is caused by germline DICER1 gene mutations. Sex cord tumors with annular tubules and Sertoli cell tumors may arise in patients with Peutz-Jeghers syndrome; this syndrome is caused by germline STK11 gene mutations. The majority of germ cell tumors develop in the context of gonadal dysgenesis. In XY gonadal dysgenesis, the presence of a Y chromosome material renders the patient at increased risk for developing gonadal malignancy. Characteristically, these patients develop gonadoblastoma, which has the potential to evolve into dysgerminoma and exhibit malignant behavior. Sex-chromosome aneuploidy syndromes or mutations in genes involved in gonadal development and differentiation may cause gonadal dysgenesis. Small cell carcinoma of the ovary of a hypercalcaemic type is usually caused by loss-of-function mutations in the SMARCA4 gene. Ovarian tumors are uncommon during childhood and adolescence. It is always necessary to consider gonadal dysgenesis or any of the inherited cancer syndromes. These patients require interdisciplinary care, careful noting of personal and family history, precise clinical examination, laboratory testing, and differential diagnosis by a clinician with a good knowledge of genetic syndromes. Expert pathological review may be required for correct diagnoses. This is necessary for appropriate management and to establish an association with hereditary cancer syndromes. The work was supported by the Ministry of Health of the Czech Republic - Conceptual Development of Research Organization, Faculty Hospital of Ostrava /2015. We thank to Lenka Foretová, M.D., Ph.D., (MMCI, Brno) and Radoslava Tomanová, M.D., (Institute of Pathology, University Hospital Ostrava) for rewarding advice, Mrs. Jana Němcová (Department of Medical Genetics, University Hospital Ostrava), Bc. Ludmila Stuchlá and Mrs. Lenka Zivčáková (Medical Library, University Hospital Ostrava) for help during manuscript preparation. The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Submitted: 10. 3. 2019 Accepted: 16. 4. 2019.

Dental abnormalities in individuals with pathogenic germline variation in DICER1.

Pathogenic germline variation in the microRNA processing gene DICER1 gives rise to an autosomal dominant, tumor-predisposition disorder. Conditional deletion of Dicer1 in murine dental epithelium shows that it controls tooth patterning, size, number, and shape. The human dental phenotype of people with germline pathogenic variation in DICER1 is unknown. DICER1-carriers (n = 57) and family controls (n = 55) were evaluated at the NIH Clinical Center dental clinic as part of a comprehensive medical evaluation. Digital panoramic radiographs, bite-wing radiographs, and oral photographs were collected. A single observer, blind to DICER1 status, reviewed the dental records and determined the presence or absence of 11 dental characteristics as described in the clinic notes, radiographs, or oral photographs. Subjective phenotypes were reviewed on radiographs by two examiners (blind to DICER1 status) for the presence or absence of the dental characteristics to reduce inconsistencies. By simple association, bulbous crown, periodontitis, and taurodontism were all significant (p < .05). Logistic regression with chi-square maximum likelihood estimates showed that bulbous crown and periodontitis remained significant. Recognition of these phenotypes may aid identification of individuals and families at risk for DICER1-associated neoplasms. These findings may also guide dental care for individuals with germline DICER1 pathogenic variation.

Germline mutations and new copy number variants among 40 pediatric cancer patients suspected for genetic predisposition.

Cancer predisposition syndromes (CPS) result from germline pathogenic variants, and they are increasingly recognized in the etiology of many pediatric cancers. Herein, we report the genetic/genomic analysis of 40 pediatric patients enrolled from 2016 to 2018. Our diagnostic workflow was successful in 50% of screened cases. Overall, the proportion of CPS in our case series is 10.9% (20/184) of enrolled patients. Interestingly, 12.5% of patients achieved a conclusive diagnosis through the analysis of chromosomal imbalance. Indeed, we observed germline microdeletions/duplications of regions encompassing cancer-related genes in 50% of patients undergoing array-CGH: EIF3H duplication in a patient with infantile desmoplastic astrocytoma and low-grade Glioma; SLFN11 deletion, SOX4 duplication, and PARK2 partial deletion in three neuroblastoma patients; a PTPRD partial deletion in a child diagnosed with glioblastoma multiforme. Finally, we identified two cases due to DICER1 germline mutations.

Gaining insights into the DICER1 syndrome: An early report from the Italian DICER1 registry.

1519 Background: DICER1 is a key endoribonuclease in the microRNA pathway that modulates gene expression. Germline loss of function variants in DICER1, first found in pleuropulmonary blastoma, have been subsequently linked to a variety of cancerous (and non) conditions referred to as DICER1 syndrome. In 2018, the Italian Society of Human Genetics launched an initiative aimed at establishing a national registry of DICER1 germline sequence variants. Methods: Centers involved in genetic testing for cancer predisposition were asked to report any identified DICER1 germline variants and related clinical information. Five University and/or research institutes filled-in the electronic survey. Informed consent was obtained from patients or their legal guardians prior to DNA testing by NGS and/or Sanger sequencing. Results: Six DICER1 sequence variants were identified in 11 individuals. Three missense variants are secondary results of NGS panels for cancer predisposition and lack definitive categorization in online databases. Three previously unreported variants are predicted to be protein truncating and, hence, likely pathogenic. Of these, DICER1 c.4844delA p.(Lys1615Argfs*5) and c.4886C &gt; G p.(Ser1629*) result from ad hoc testing offered to probands based on a history of early onset follicular thyroid carcinoma and botryoid-type embryonal rhabdomyosarcoma of the cervix and of pleuropulmonary blastoma 2nd type, respectively. DICER1 c.4643T &gt; A p.(Leu1548*), instead, results from whole exome sequencing in two siblings with malignant melanoma who tested non informative for alterations in the CDKN2A and CDK4 melanoma predisposing genes. Further investigation unearthed thyroid disease in the family and identified two other young carrier individuals, one unaffected and one thyroidectomized due to multinodular goiter. A DICER1 somatic hot spot sequence variant was detected in goiter specimens. Conclusions: Via the newly established national registry we uncovered novel DICER1 germline sequence variants and uncommon genotype-phenotype associations. Our joint effort will help us to refine our knowledge of the rare DICER1 syndrome , to inform research studies, and to improve testing and clinical management strategies.

Dicer1 Phosphomimetic Promotes Tumor Progression and Dissemination.

Dicer1 functions as a tumor suppressor in mouse models. In humans, somatic mutations are associated with many cancers in adults, and patients with DICER1 syndrome with DICER1 germline mutations are susceptible to childhood cancers. Dicer is phosphorylated by the ERK-MAP kinase pathway and because this pathway is activated in human cancers, we asked whether phosphorylated Dicer1 contributed to tumor development. In human endometrioid cancers, we discovered that phosphorylated DICER1 is significantly associated with invasive disease. To test a direct involvement of Dicer1 phosphorylation in tumor development, we studied mice with phosphomimetic alterations at the two conserved serines phosphorylated by ERK and discovered that a phosphomimetic Dicer1 drives tumor development and dissemination in two independent murine cancer models (KRas+/LA1 and p53+/- ). Our findings demonstrate that phosphomimetic Dicer1 promotes tumor development and invasion. SIGNIFICANCE: This work highlights the relevance of Dicer1 phosphorylation in mammalian tumor development and dissemination.

Mesenchymal Hamartoma of the Liver and DICER1 Syndrome

SummaryMesenchymal hamartoma of the liver (MHL) is a benign tumor affecting children that is characterized by a primitive myxoid stroma with cystically dilated bile ducts. Alterations involving chromosome 19q13 are a recurrent underlying cause of MHL; these alterations activate the chromosome 19 microRNA cluster (C19MC). Other cases remain unexplained. We describe two children with MHLs that harbored germline DICER1 pathogenic variants. Analysis of tumor tissue from one of the children revealed two DICER1 “hits.” Mutations in DICER1 dysregulate microRNAs, mimicking the effect of the activation of C19MC. Our data suggest that MHL is a new phenotype of DICER1 syndrome. (Funded by the Canadian Institutes of Health Research and others.)

SUN-047 Germline and Somatic Mutations in DICER1 Gene Associated with Different Hereditary Tumours in Paediatric Patients

Carriers of germline DICER1 mutations are predisposed to a rare cancer syndrome, the DICER1 syndrome, associated with tumours such as pleuropulmonary blastoma (PPB), ovarian Sertoli-Leydig cell tumours (SLCT), multinodular goiter (MNG), cystic nephroma (CN), embryonal rhabdomyosarcoma (ERMS) and others. Germline mutations in DICER1 cause an alteration in miRNAs processing, deregulating target oncogenes and leading to elevated risk of tumorigenesis. In most reported cases, there is a heterozygous germline mutation and a somatic second hit mutation. Aim: Analyze the presence of germline and somatic alterations in the DICER1 gene in 6 patients with paediatric tumours associated with DICER1 spectrum. Methods: Automated sequencing of DICER1 gene from gDNA extracted from blood and formalin-fixed, paraffin-embedded tumour tissues of affected subjects and relatives. Cases: 5 girls (P1-P5) and 1 boy (P6), (P1: bilateral SLCT, P2 and P3: SLCT and MNG, P4: MNG and uterine myosarcoma, P5: vaginal rhabdomyosarcoma, and P6: CN). Chronological age at diagnostic was 5, 12, 15, 16, 13 y 2, respectively. Results: We detected 5 novel heterozygous mutations: p.Trp1098* in P1, p.Phe351fs*1 in P2, p.Arg1596Glyfs*24 in P4, c.3269+1G>A in P5, p.Asp244Glyfs*27 in P6, and one previously described heterozygous deletion p.Asp1437Metfs*16 in P3.These mutations (P1-P4 and P6) predict the presence of a truncated protein losing its essential domains for the enzymatic activity and, in one P5 an alteration in the splicing process. The tissue analysis revealed p.Asp1709Glu in MNG and p.Glu1705Lys in SLCT in P2, and p.Glu1705Lys in MNG in P3,previously described as hotspot somatic mutations. Conclusions: We report five novel germinal mutations in DICER1 gene and two somatic hotspot mutations in MNG and SLCT tissue samples. These findings confirm that a second hit event is involved in the mechanism of MNG and SLCT development. Molecular analysis of DICER1 gene allows to perform genetic counselling about familial recurrence risk.

SUN-284 DICER1 Mutations in Adolescent Girls: Clinicopathological Findings and Genetic Correlation

Background: The DICER1 syndrome is a rare tumor predisposition disorder associated with multinodular goiter (MNG), differentiated thyroid cancer, ovarian Sertoli-Leydig cell tumor, pleuropulmonary blastoma and pituitary blastoma (1,2). The DICER1 gene encodes the endoribonuclease protein of the ribonuclease III family which acts post-transcriptionally to downregulate messenger RNAs. Both germline and somatic mutations have been reported (3). We describe 2 previously healthy unrelated females referred for evaluation of thyroid nodules. Cases:Case 1: A 16yo female presented with spontaneous passage of polyps at her menstrual period. Histologic analysis revealed embryonal rhabdomyosarcoma. Her primary malignancy, confined to the cervix, was treated with surgical resection followed by chemotherapy. Staging evaluation revealed a left thyroid nodule. FNA of the nodule showed follicular patterned lesion with cytologic atypia; molecular testing was positive for DICER1 somatic mutation (c.5429A;p.D1810V). Peripheral blood genetic testing was positive for a heterozygous DICER1 germline mutation (1510-1G>A). She underwent left lobectomy; histology showed encapsulated papillary carcinoma. Case 2: A 13yo female developed a sudden non-tender neck mass. Ultrasound-guided FNA of the solid lesion in the left thyroid lobe revealed atypia of undetermined significance. Molecular studies identified a DICER1 gene mutation (c.5126A>G; p.D1709G). A peripheral blood sample showed heterozygous DICER1 mutation (c.1870C>T;pArg624*). Three 1st degree family members were also positive for the germline mutation. She underwent total thyroidectomy; pathology revealed MNG with a predominant hyperplastic nodule. Conclusion: Two adolescents with thyroid lesions were positive for DICER1 mutations (4). The prevalence of DICER1 mutations, natural history, and extent of phenotypic heterogeneity are unknown. Two mutations, one germline and one somatic, were identified in our patients. Enhanced molecular testing (ThyroSeqv3) is now available to identify mutations. Testing thyroid nodules for DICER1 mutations (5-7), followed by screening for germline mutations in positive cases is essential to identify patients at risk of other manifestations and to ensure surveillance. Scrutiny of cases will help elucidate the natural history of DICER1 syndrome and establish guidelines regarding the extent and frequency of screening.

DICER1 Mutations in the Era of Expanding Integrative Clinical Sequencing in Pediatric Oncology.

DICER1 syndrome is a recently described inherited cancer predisposition syndrome caused by pathogenic variants in DICER1. With the recent increase in integrative clinical sequencing for pediatric patients with cancer, our understanding of the DICER1 syndrome continues to evolve, as new and rare pathogenic variants are reported. As the frequency of integrative clinical sequencing increases, discussions regarding challenges encountered in the interpretation of sequencing results are essential to continue to advance the field of cancer predisposition. The purpose of this work was to identify patients with somatic and/or germline DICER1 variants in our patient population and to discuss sequencing interpretation and the clinical recommendations that result from the integrative clinical sequencing results. Patients were enrolled in the PEDS-MIONCOSEQ study. This integrative clinical sequencing study includes paired tumor/normal whole-exome sequencing and tumor transcriptome sequencing. Patients identified as having DICER1 variants were included. We report a DICER1 variant of unknown clinical significance in a patient with a highly unusual response to therapy. Two patients had diagnoses clarified once the integrative clinical sequencing revealing a DICER1 variant was available. We also discovered a patient with low-level DICER1 mosaicism and the challenges encountered in the sequencing interpretation for this patient. In addition to the sequencing data and result interpretation, this work also highlights testing and screening recommendations made to patients with DICER1 variants and their families on the basis of these results. This work serves to extend the DICER1 phenotype and advance the utility of clinical integrative sequencing in the fields of pediatric oncology and cancer genetic predisposition.

Retiform Sertoli-Leydig cell tumour and dicer1 germline mutation syndrome

Retiform Sertoli-Leydig cell tumour and dicer1 germline mutation syndrome

The prevalence of germline DICER1 pathogenic variation in cancer populations.

BackgroundThe DICER1 syndrome is an autosomal dominant tumor‐predisposition disorder associated with pleuropulmonary blastoma, a rare pediatric lung cancer. Somatic missense variation in “hotspot” codons in the RNaseIIIb domain (E1705, D1709, G1809, D1810, E1813) is observed in DICER1‐associated tumors. Previously, we found the prevalence of germline pathogenic DICER1 variation in the general population is 1:10,600. In this study, we investigated the prevalence of pathogenic DICER1 germline variation in The Cancer Genome Atlas (TCGA; 32 adult cancer types; 9,173 exomes) and the Therapeutically Applicable Research to Generate Effective Treatment (TARGET; two pediatric cancer types; 175 exomes) cohorts.MethodsAll datasets were annotated and binned into four categories: pathogenic, likely pathogenic, variant of unknown significance, or likely benign.ResultsThe prevalence of DICER1 pathogenic variants was 1:4,600 in TCGA. A single participant with a uterine corpus endometrial carcinoma harbored two pathogenic germline DICER1 (hotspot and splice‐donor) variants, and a single participant with a rectal adenocarcinoma harbored a germline DICER1 stop‐gained variant. In the smaller TARGET dataset, we observed no pathogenic germline variants.ConclusionThis is the largest comprehensive analysis of DICER1 pathogenic variation in adult and pediatric cancer populations using publicly available data. The observation of germline DICER1 variation with uterine corpus endometrial carcinoma merits additional investigation.

Primary Lung Tumors in Children: Radiologic-Pathologic Correlation From the Radiologic Pathology Archives.

Primary lung tumors in children are rare, with a narrow range of diagnostic considerations. However, the overlapping imaging appearances of these tumors necessitate attention to key discriminating imaging and pathologic features. In the neonate and infant, the important considerations include pleuropulmonary blastoma (PPB), infantile fibrosarcoma, and fetal lung interstitial tumor. Among these tumors, imaging findings such as air-filled cysts in type 1 PPB and homogeneously low attenuation of fetal lung interstitial tumors are relatively specific. Key pathologic and genetic discriminators among this group of tumors include the DICER1 germline mutation found in PPB and the t(12,15)(p13;q25) translocation and ETV6-NTRK3 fusion gene seen in infantile fibrosarcoma. Primary lung tumors in older children include inflammatory myofibroblastic tumors (IMTs), carcinoid salivary gland-type tumors of the lung, recurrent respiratory papillomatosis, and other rare entities. IMT, a spindle-cell proliferation with inflammatory elements, is the most common lung tumor in children. Anaplastic lymphoma kinase, a receptor-type protein tyrosine kinase, is present in 50% of these tumors, and this finding may support an imaging diagnosis of IMT. Carcinoid tumors account for a substantial portion of childhood lung tumors, and their characteristic avid enhancement on images corresponds to the compressed fibrovascular stroma histologically. Furthermore, novel imaging agents used with somatostatin receptor analogs have an emerging role in the evaluation of carcinoid tumors. Although less common than mucoepidermoid carcinoma, adenoid cystic carcinoma tends to recur given the perineural spread seen histologically. Integrating radiologic and pathologic knowledge is critical to accurate diagnosis, treatment planning, and surveillance of primary lung tumors in children.

DICER1 mutation and pituitary prolactinoma

SummaryA young woman carrying germline DICER1 mutation was discovered to have a pituitary microprolactinoma when she became amenorrhoic. The mutation was identified as a result of family screening following the early death of the patient’s daughter with ovarian cancer. The patient was in follow-up screening for thyroid disease, and investigations were initiated when she became amenorrhoic. MR scan revealed a 6 mm diameter pituitary microadenoma and raised prolactin. The prolactin was efficiently suppressed with low-dose cabergoline, and her menstrual cycles resumed. Dicer is an RNase enzyme, which is essential for processing small non-coding RNAs. These molecules play pleiotropic roles in regulating gene expression, by targeting mRNA sequences for degradation. DICER1 plays different roles depending on cell context, but is thought to be a functional tumour suppressor gene. Accordingly, germline mutation in one DICER1 allele is insufficient for oncogenesis, and a second hit on the other allele is required, as a result of postnatal somatic mutation. Loss of DICER1 is linked to multiple tumours, with prominent endocrine representation. Multinodular goitre is frequent, with increased risk of differentiated thyroid cancer. Rare, developmental pituitary tumours are reported, including pituitary blastoma, but not reports of functional pituitary adenomas. As DICER1 mutations are rare, case reports are the only means to identify new manifestations and to inform appropriate screening protocols.Learning points:DICER1 mutations lead to endocrine tumours.DICER1 is required for small non-coding RNA expression.DICER1 carriage and microprolactinoma are both rare, but here are reported in the same individual, suggesting association.Endocrine follow-up of patients carrying DICER1 mutations should consider pituitary disease.

DICER1 mutations are frequent in adolescent-onset papillary thyroid carcinoma

Thyroid cancer in children and adolescents has a higher rate of regional and distant metastases, and recurrence rate than in adults. However, little is known about the molecular origin of thyroid carcinoma in children. DICER1 encodes for an endoribonuclease responsible for processing RNA into small interfering RNA vand miRNA. DICER1 syndrome (OMIM #601200) has been recently described resulting from truncating mutations in the DICER1 gene causing a wide spectrum of benign and malignant tumors in children, such as pleuropulmonary blastoma, cystic nephroma, and pituitary blastoma. The risk for multinodular goiter and thyroid cancer in DICER1 germline mutation carriers has recently been shown to be highly increased1.

Abstract 2070: The prevalence of DICER1 pathogenic variation in cancer population databases

Abstract DICER1 is an RNaseIII endonuclease that is crucial for processing pre-microRNA into mature microRNA. The DICER1 syndrome is a rare, autosomal dominant tumor-predisposition disorder associated with pleuropulmonary blastoma, a rare pediatric lung cancer. Somatic missense variation in “hotspot” codons in the RNaseIIIb domain (E1705, D1709, G1809, D1810, E1813) is observed in DICER1-associated tumors. Previously, we found in the general population (non-TCGA ExAC) that the prevalence of pathogenic DICER1 variation is approximately 1:10,000. In this study, we investigated the prevalence of pathogenic DICER1 variation in common adult and pediatric cancers. We examined two publicly-available cancer datasets: TCGA (adult; 32 cancer types; 9,173 exomes) and TARGET (pediatric; 3 cancer types; 236 exomes). TCGA bam files were downloaded and germline variants were called. Germline VCF files were obtained from TARGET investigators. All datasets were annotated with snpEff and ANNOVAR. Variants were binned into 4 categories: likely benign (LB), variant of unknown significance (VUS), likely pathogenic (LP), or pathogenic (P). We reviewed publicly-available pathology images for the TCGA tumors. The prevalence of DICER1 P/LP variants (in all cancers combined) was 1:834 and 1:118 in TCGA and TARGET, respectively. To reduce potential prevalence inflation, we conducted a more stringent prevalence calculation by only considering loss-of-function and hotspot variants. The prevalence of P variants was approximately 1:4586 in TCGA and 1:236 in TARGET. With these more stringent criteria, a single participant with a uterine corpus endometrial carcinoma (UCEC in TCGA) harbored a two pathogenic germline DICER1 (hotspot and splice donor) variants, and a second UCEC harbored a somatic DICER1 (hotspot) variant. In TARGET, a single participant with a neuroblastoma harbored a germline DICER1 canonical splice variant. There were no atypical or unusual features noted on pathology review of publicly-available slides from TCGA tumors. In TCGA, across many types of cancer, the prevalence of pathogenic DICER1 variation was higher compared with the general population (~1:4,600 vs. ~1:10,000), a finding driven by one cancer type (UCEC). In the smaller TARGET dataset, we observed a single pathogenic germline variant in neuroblastoma. This is the first comprehensive analysis of DICER1 pathogenic variation in large adult and pediatric cancer populations. The novel association of DICER1 variation with UCEC merits additional investigation. Citation Format: Jung Kim, Kris Ann P. Schultz, D. Ashley A. Hill, Douglas R. Stewart. The prevalence of DICER1 pathogenic variation in cancer population databases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2070.

Abstract 4605: DICER1 mutations are associated with diverse and frequently histologically mixed-type malignancies in young and adult patients

Abstract Introduction: DICER1 is a ribonuclease III enzyme that processes pre-microRNAs into mature 20-23 nucleotide microRNAs required for their normal function. Heterozygous germline DICER1 loss-of-function mutations are associated with a cancer predisposition syndrome in which affected individuals present at a young age with rare neoplasms including pleuropulmonary blastoma (PPB), pineoblastoma, embryonal rhabdomyosarcoma (ERMS), Sertoli-Leydig cell tumors (SLCT) and thyroid hyperplasia. These tumors have secondary somatic missense mutations in the remaining DICER1 allele in exons 24 and 25 encoding the RNAse IIIb domain. Contribution of DICER1 somatic mutations to carcinogenesis in the adult population is largely unknown. Methods: Caris Life Sciences (Phoenix, AZ) database of over 25,000 human cancers containing complete gene sequences of 592 genes (NGS) was searched for mutations in DICER1 gene. Histologic (H&amp;E) slides were reviewed for morphologic characteristics of tumors associated with DICER1 mutations. Results: 31 patients with biallelic pathogenic DICER1 mutations were identified (approximate frequency of 0.1% in the studied cohort of all cancer types). Female to male ratio was 30:1; age range was from 3 to 79 years of age. The most common primary site was in the endometrium/uterus (15), followed by ovary (8), lung (3), cervix, brain, kidney, retroperitoneum and thyroid (1 each). Majority of endometrial malignancies were observed in adult women (N=15; age 17-79 y. o.), of whom 7 presented with mixed epithelial-mesenchymal type malignancies (carcino- and adeno-sarcomas). Most common (7) ovarian malignancy was SLCT (with and without sarcomatoid elements). One male patient presented with epithelioid glioblastoma (48 y. o.). Three lung cancers seen in adults (39 and two 74 y. o.) were PPB, adenocarcinoma NOS and mucinous adenocarcinoma, respectively. Kidney neproblastoma and cervical ERMS with heterologous elements were observed in 3 and 50 y. o. females, respectively. Overall, DICER1 mutated tumors exhibited low mutational load with the exception of one endometrial adenocarcinoma associated with POLE/MSH6 mutations. Conclusion: Biallelic somatic DICER1 mutations can be found in tumors of adult patients and are frequently associated with mixed-type malignancies. Sarcomatoid tumor elements were detected not just in endometrial malignancies, but in 2 SLCTs, cervical and thyroid malignancies. These findings are consistent with a recently reported role of DICER1 in epithelial-to-mesenchymal transition (EMT) in experimental cancers, and tumors with such histology should prompt investigations into DICER1 status. Citation Format: Zoran Gatalica, Michelle Ellis, Jeff Swensen. DICER1 mutations are associated with diverse and frequently histologically mixed-type malignancies in young and adult patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4605.

Primary intracranial spindle cell sarcoma with rhabdomyosarcoma-like features share a highly distinct methylation profile and DICER1 mutations.

Patients with DICER1 predisposition syndrome have an increased risk to develop pleuropulmonary blastoma, cystic nephroma, embryonal rhabdomyosarcoma, and several other rare tumor entities. In this study, we identified 22 primary intracranial sarcomas, including 18 in pediatric patients, with a distinct methylation signature detected by array-based DNA-methylation profiling. In addition, two uterine rhabdomyosarcomas sharing identical features were identified. Gene panel sequencing of the 22 intracranial sarcomas revealed the almost unifying feature of DICER1 hotspot mutations (21/22; 95%) and a high frequency of co-occurring TP53 mutations (12/22; 55%). In addition, 17/22 (77%) sarcomas exhibited alterations in the mitogen-activated protein kinase pathway, most frequently affecting the mutational hotspots of KRAS (8/22; 36%) and mutations or deletions of NF1 (7/22; 32%), followed by mutations of FGFR4 (2/22; 9%), NRAS (2/22; 9%), and amplification of EGFR (1/22; 5%). A germline DICER1 mutation was detected in two of five cases with constitutional DNA available. Notably, none of the patients showed evidenceof a cancer-related syndrome at the time of diagnosis. In contrast to the genetic findings, the morphological features of these tumors were less distinctive, although rhabdomyoblasts or rhabdomyoblast-like cells could retrospectively be detected in all cases. The identified combination of genetic events indicates a relationship between the intracranial tumors analyzed and DICER1 predisposition syndrome-associated sarcomas such as embryonal rhabdomyosarcoma or the recently described group of anaplastic sarcomas of the kidney. However, the intracranial tumors in our series were initially interpreted to represent various tumor types, but rhabdomyosarcoma was not among thetypical differential diagnoses considered. Given the rarity of intracranial sarcomas, this molecularly clearly defined group comprises a considerable fraction thereof. We therefore propose the designation "spindle cell sarcoma with rhabdomyosarcoma-like features, DICER1 mutant" for this intriguing group.

Carcinome papillaire thyroïdien variante solide/trabéculaire avec mutation DICER1 chez une enfant de 11 ans

We report the case of an 11-year-old patient diagnosed with a solid variant of papillary thyroid carcinoma. Papillary thyroid carcinoma (PTC) is the most common thyroid cancer, representing 80-90% of all newly diagnosed thyroid cancers. Among the many variants described, solid/trabecular variant of papillary thyroid carcinoma is a rare entity and account for 3% of thyroid cancers. It is more common in children and young adults, and it is seen in higher proportion in post radiation papillary thyroid carcinoma cases. Histologically, solid variant papillary carcinoma is characterized by a predominantly solid, trabecular or insular growth pattern, and the presence of cytological features typical of PTC. Its main differential diagnosis is poorly differentiated thyroid carcinoma. It has a less favorable prognosis than the classical papillary type, with a higher risk of distant metastasis, extrathyroidal extension and lympho-vascular invasion. It is associated with a slightly lower long-term survival in adult cases, but not in children. The management of solid variant PTC includes surgery, associated or not with postoperative radioiodine ablation, according to the aggressiveness criteria. Our patient had a DICER1 somatic mutation. Carriers of germline DICER1 mutations are predisposed to a rare cancer syndrome, the DICER1 syndrome, with a higher risk of numerous tumors and infrequently differentiated thyroid carcinomas.