DICER1 mutations in familial pleuropulmonary blastoma

Hotspots of Somatic Genetic Variation in Pituitary Neuroendocrine Tumors

The most common genetic drivers of pituitary neuroendocrine tumors (PitNETs) lie within mutational hotspots, which are genomic regions where variants tend to cluster. Some of these hotspot defects are unique to PitNETs, while others are associated with additional neoplasms. Hotspot variants in GNAS and USP8 are the most common genetic causes of acromegaly and Cushing's disease, respectively. Although it has been proposed that these genetic defects could define specific clinical phenotypes, results are highly variable among studies. In contrast, DICER1 hotspot variants are associated with a familial syndrome of cancer predisposition, and only exceptionally occur as somatic changes. A small number of non-USP8-driven corticotropinomas are due to somatic hotspot variants in USP48 or BRAF; the latter is a well-known mutational hotspot in cancer. Finally, somatic variants affecting a hotspot in SF3B1 have been associated with multiple cancers and, more recently, with prolactinomas. Since the associations of BRAF, USP48, and SF3B1 hotspot variants with PitNETs are very recent, their effects on clinical phenotypes are still unknown. Further research is required to fully define the role of these genetic defects as disease biomarkers and therapeutic targets.

miRNA-Based Technologies in Cancer Therapy

The discovery of therapeutic miRNAs is one of the most exciting challenges for pharmaceutical companies. Since the first miRNA was discovered in 1993, our knowledge of miRNA biology has grown considerably. Many studies have demonstrated that miRNA expression is dysregulated in many diseases, making them appealing tools for novel therapeutic approaches. This review aims to discuss miRNA biogenesis and function, as well as highlight strategies for delivering miRNA agents, presenting viral, non-viral, and exosomic delivery as therapeutic approaches for different cancer types. We also consider the therapeutic role of microRNA-mediated drug repurposing in cancer therapy.

Infantile type I pleuropulmonary blastoma presenting with dyspnea due to compression by pneumothorax and an occupying tumor: a case report

BACKGROUND

Pleuropulmonary blastoma (PPB) is an extremely rare and malignant pediatric lung tumor. Purely cystic PPB has a more favorable prognosis than solid PPB, but may be difficult to distinguish from a certain type of "benign" congenital pulmonary airway malformation before and during surgery. The influence of tumor rupture on long life prognosis has not been clarified in detail.

CASE PRESENTATION

A 5-month-old boy underwent emergency transfer from another hospital due to a left thoracic cystic lesion and left pneumothorax detected on chest radiography performed for persistent wheeze and cough. Contrast-enhanced computed tomography of the chest revealed marked deviation of the mediastinum to the right due to a giant cystic lesion and pneumothorax. Thoracotomy was performed on hospital day 2. A cystic lesion had developed from the distal alveolar region of lower lobe of the left lung and the tumor showed a tiny adhesion to the left diaphragm and a tiny rupture near the adhesion. Partial lung excision including the cyst and scraping of the adhesion were performed. Histopathological investigations revealed immature blast cell-like mesenchymal cells and differentiated striated muscle cells in a dense cambium layer were found under the epithelium of the cystic lesion. Type I PPB was diagnosed.

CONCLUSIONS

Surgery should be performed with the possibility of type I PPB in mind when an extrapulmonary cystic lung lesion is found. Since issues such as the pathogenesis and long-term prognosis of ruptured cases remain unclear, continued careful follow-up of this case will be required.

Progress in Thyroid Cancer Genomics: A 40-Year Journey

Background: Very little was known about the molecular pathogenesis of thyroid cancer until the late 1980s. As part of the Centennial celebration of the American Thyroid Association, we review the historical discoveries that contributed to our current understanding of the genetic underpinnings of thyroid cancer. Summary: The pace of discovery was heavily dependent on scientific breakthroughs in nucleic acid sequencing technology, cancer biology, thyroid development, thyroid cell signaling, and growth regulation. Accordingly, we attempt to link the primary observations on thyroid cancer molecular genetics with the methodological and scientific advances that made them possible. Conclusions: The major genetic drivers of the common forms of thyroid cancer are now quite well established and contribute to a significant extent to how we diagnose and treat the disease. However, many challenges remain. Future work will need to unravel the complexity of thyroid cancer ecosystems, which is likely to be a major determinant of their biological behavior and on how they respond to therapy.

Biallelic Dicer1 Mutations in the Gynecologic Tract of Mice Drive Lineage-Specific Development of DICER1 Syndrome-Associated Cancer

DICER1 is an RNase III enzyme essential for miRNA biogenesis through cleaving precursor-miRNA hairpins. Germline loss-of-function DICER1 mutations underline the development of DICER1 syndrome, a rare genetic disorder that predisposes children to cancer development in organs such as lung, gynecologic tract, kidney, and brain. Unlike classical tumor suppressors, the somatic "second hit" in DICER1 syndrome-associated cancers does not fully inactivate DICER1 but impairs its RNase IIIb activity only, suggesting a noncanonical two-hit hypothesis. Here, we developed a genetically engineered conditional compound heterozygous Dicer1 mutant mouse strain that fully recapitulates the biallelic DICER1 mutations in DICER1 syndrome-associated human cancers. Crossing this tool strain with tissue-specific Cre strains that activate Dicer1 mutations in gynecologic tract cells at two distinct developmental stages revealed that embryonic biallelic Dicer1 mutations caused infertility in females by disrupting oviduct and endometrium development and ultimately drove cancer development. These multicystic tubal and intrauterine tumors histologically resembled a subset of DICER1 syndrome-associated human cancers. Molecular analysis uncovered accumulation of additional oncogenic events (e.g., aberrant p53 expression, Kras mutation, and Myc activation) in murine Dicer1 mutant tumors and validated miRNA biogenesis defects in 5P miRNA strand production, of which, loss of let-7 family miRNAs was identified as a putative key player in transcriptomic rewiring and tumor development. Thus, this DICER1 syndrome-associated cancer model recapitulates the biology of human cancer and provides a unique tool for future investigation and therapeutic development.

SIGNIFICANCE

Generation of a Dicer1 mutant mouse model establishes the oncogenicity of missense mutations in the DICER1 RNase IIIb domain and provides a faithful model of DICER1 syndrome-associated cancer for further investigation.

[DICER1 syndrome: clinical variety endocrine manifestations and features of diagnostics]

DICER1 syndrome is a rare genetic disorder with the progressive development of malignant and non-malignant diseases in childhood. The cause of this syndrome is a dusfunction of the endoribonuclease DICER, which plays an important role in the processing of microRNAs with subsequent regulation of the control of the expression of oncogenes and tumor suppressor genes. Clinical manifestations of dyseropathies is very different and may include both endocrine manifestations - multinodular goiter, differentiated thyroid cancers, ovarian stromal tumors, pituitary blastoma, and non-endocrine formations - pleuropulmonary blastoma, cystic nephroma, pineoblastoma. The presence of somatic mutations of the DICER1 gene is a resultant stage in the pathogenesis of dyseropathies, determining the further path of oncogenesis. At present, DICER1 syndrome is diagnosed extremely rarely, which leads to late detection of the components of the disease in the patient, late diagnosis of neoplasms, lack of family counseling. Diagnosis at the early stages of the disease, the development of screening programs for the management of these patients allows minimizing the risks of developing more malignant, aggressive forms of the disease.

Cellular functions of eukaryotic RNA helicases and their links to human diseases

RNA helicases are highly conserved proteins that use nucleoside triphosphates to bind or remodel RNA, RNA-protein complexes or both. RNA helicases are classified into the DEAD-box, DEAH/RHA, Ski2-like, Upf1-like and RIG-I families, and are the largest class of enzymes active in eukaryotic RNA metabolism - virtually all aspects of gene expression and its regulation involve RNA helicases. Mutation and dysregulation of these enzymes have been linked to a multitude of diseases, including cancer and neurological disorders. In this Review, we discuss the regulation and functional mechanisms of RNA helicases and their roles in eukaryotic RNA metabolism, including in transcription regulation, pre-mRNA splicing, ribosome assembly, translation and RNA decay. We highlight intriguing models that link helicase structure, mechanisms of function (such as local strand unwinding, translocation, winching, RNA clamping and displacing RNA-binding proteins) and biological roles, including emerging connections between RNA helicases and cellular condensates formed through liquid-liquid phase separation. We also discuss associations of RNA helicases with human diseases and recent efforts towards the design of small-molecule inhibitors of these pivotal regulators of eukaryotic gene expression.

Intronic Germline DICER1 Variants in Patients With Sertoli-Leydig Cell Tumor

Germline pathogenic loss-of-function (pLOF) variants in DICER1 are associated with a predisposition for a variety of solid neoplasms, including pleuropulmonary blastoma and Sertoli-Leydig cell tumor (SLCT). The most common DICER1 pLOF variants include small insertions or deletions leading to frameshifts, and base substitutions leading to nonsense codons or altered splice sites. Larger deletions and pathogenic missense variants occur less frequently. Identifying these variants can trigger surveillance algorithms with potential for early detection of DICER1-related cancers and cascade testing of family members. However, some patients with DICER1-associated tumors have no pLOF variants detected by germline or tumor testing. Here, we present two patients with SLCT whose tumor sequencing showed only a somatic missense DICER1 RNase IIIb variant. Conventional exon-directed germline sequencing revealed no pLOF variants. Using a custom capture panel, we discovered novel intronic variants, ENST00000343455.7: c.1752+213A>G and c.1509+16A>G, that appear to interfere with normal splicing. We suggest that when no DICER1 pLOF variants or large deletions are discovered in exonic regions despite strong clinical suspicion, intron sequencing and splicing analysis should be performed.

Spontaneous pneumothorax or no pneumothorax at all?

Care of a simple pneumothorax in a paediatric patient is often anything but simple, and a refractory and complex pneumothorax requires thoughtful and deliberate care https://bit.ly/3NFAk9S.

Simultaneous Occurrence of Multiple Neoplasms in Children with Cancer Predisposition Syndromes: Collaborating with Abnormal Genes

The identification of cancer predisposition syndromes (CPSs) plays a crucial role in understanding the etiology of pediatric cancers. CPSs are genetic mutations that increase the risk of developing cancer at an earlier age compared to the risk for the general population. This article aims to provide a comprehensive analysis of three unique cases involving pediatric patients with CPS who were diagnosed with multiple simultaneous or metachronous cancers. The first case involves a child with embryonal rhabdomyosarcoma, nephroblastoma, glioma, and subsequent medulloblastoma. Genetic analysis identified two pathogenic variants in the BRCA2 gene. The second case involves a child with alveolar rhabdomyosarcoma, juvenile xanthogranuloma, gliomas, and subsequent JMML/MDS/MPS. A pathogenic variant in the NF1 gene was identified. The third case involves a child with pleuropulmonary blastoma and pediatric cystic nephroma/nephroblastoma, in whom a pathogenic variant in the DICER1 gene was identified. Multiple simultaneous and metachronous cancers in pediatric patients with CPSs are a rare but significant phenomenon. Comprehensive analysis and genetic testing play significant roles in understanding the underlying mechanisms and guiding treatment strategies for these unique cases. Early detection and targeted interventions are important for improving outcomes in these individuals.

DICER1 Syndrome: A Multicenter Surgical Experience and Systematic Review

DICER1 syndrome is a rare genetic disorder that predisposes patients to the development of malignant and non-malignant diseases. Presently, DICER1 syndrome diagnosis still occurs late, usually following surgical operations, affecting patients' outcomes, especially for further neoplasms, which are entailed in this syndrome. For this reason, herein we present a multicenter report of DICER1 syndrome, with the prospective aim of enhancing post-surgical surveillance. A cohort of seven patients was collected among the surgical registries of Pediatric Surgery at the University of Pisa with the General and Oncologic Surgery of Federico II, University of Naples, and the Pediatric Surgery, Regina Margherita Hospital, University of Turin. In each case, the following data were analyzed: sex, age at diagnosis, age at first surgery, clinical features, familial, genetic investigations, and follow-up. A comprehensive literature review of DICER1 cases, including case reports and multicenter studies published from 1996 to June 2022, was performed. Eventually, the retrieved data from the literature were compared with the data emerging from our cohort of patients.

A Case of Primary Intracranial Sarcoma, DICER1-Mutant, in a Child with a Germline DICER1 Mutation

DICER1 syndrome is a tumor predisposition syndrome caused by abnormal micro-RNA processing which leads to a variety of benign and malignant neoplasms in many organ systems, including the central nervous system. This paper reports the case of a primary intracranial sarcoma, DICER1-mutant, in a patient with a germline DICER1 variant thought most likely to be de novo. The patient is a ten-year-old boy who presented acutely with altered level of consciousness, emesis, and left-sided weakness. Imaging revealed a large right frontal hemorrhagic lesion, which was urgently debulked. Histology demonstrated a high-grade sarcomatous lesion. Molecular studies revealed compound heterozygous DICER1 variants (a frame shift insertion and a missense mutation), and a KRAS missense mutation. The final pathologic diagnosis was rendered to be "primary intracranial sarcoma, DICER1-mutant". Germline genetic testing revealed that the patient possessed a germline DICER1 variant (parental testing was negative). A dramatic reduction in tumor size was precipitated via chemotherapy (ifosfamide, carboplatin, and etoposide) and radiotherapy (focal proton beam therapy). There was no evidence of residual disease at the primary site at the end of the therapy.

A rare case of Pleuropulmonary blastoma type III with Immunohistochemical Study

Here we intend to document a rare case of PPB type III in a 2-year male presenting with an extensive tumor occupying the right hemithorax with immunohistochemical (IHC) study. Pleuropulmonary blastoma (PPB) is a rare variably aggressive, dysodontogenetic, childhood primary intrathoracic malignancy which in up to 25% of cases can be extrapulmonary with attachment to the parietal pleura. It is found in pediatric population under 5 years of age. It was initially proposed as a distinct entity by Manivel et al. in 1988. PPB is a proliferation of primitive mesenchymal cells that initially form air-filled cysts lined by benign-appearing epithelium (type I, cystic). Later on, the mesenchymal cells outgrow the cysts with formation of focal solid areas (type II, solid and cystic) and finally, mainly solid mass (type III, solid PPB).

Comparative Biochemical Studies of Disease-Associated Human Dicer Mutations on Processing of a Pre-microRNA and snoRNA

Dicer is an RNase III enzyme that is responsible for the maturation of small RNAs such as microRNAs. As Dicer's cleavage products play key roles in promoting cellular homeostasis through the fine-tuning of gene expression, dysregulation of Dicer activity can lead to several human diseases, including cancers. Mutations in Dicer have been found to induce tumorigenesis and lead to the development of a rare pleiotropic tumor predisposition syndrome found in children and young adults called DICER1 syndrome. These patients harbor germline and somatic mutations in Dicer that lead to defective microRNA processing and activity. While most mutations occur within Dicer's catalytic RNase III domains, alterations within the Platform-PAZ (Piwi-Argonaute-Zwille) domain also cause loss of microRNA production. Using a combination of in vitro biochemical and cellular studies, we characterized the effect of disease-relevant Platform-PAZ-associated mutations on the processing of a well-studied oncogenic microRNA, pre-microRNA-21. We then compared these results to those of a representative from another Dicer substrate class, the small nucleolar RNA, snord37. From this analysis, we provide evidence that mutations within the Platform-PAZ domain result in differential impacts on RNA binding and processing, adding new insights into the complexities of Dicer processing of small RNA substrates.

Update on Ovarian Sex Cord-Stromal Tumors

This article focuses on the recent advances in ovarian sex cord-stromal tumors, predominantly in the setting of their molecular underpinnings. The integration of genetic information with morphologic and immunohistochemical findings in this rare subset of tumors is of clinical significance from refining the diagnostic and prognostic stratifications to genetic counseling.

KRAS Hijacks the miRNA Regulatory Pathway in Cancer

Extensive studies have focused on the misregulation of individual miRNAs in cancer. More recently, mutations in the miRNA biogenesis and processing machinery have been implicated in several malignancies. Such mutations can lead to global miRNA misregulation, which may promote many of the well-known hallmarks of cancer. Interestingly, recent evidence also suggests that oncogenic Kristen rat sarcoma viral oncogene homolog (KRAS) mutations act in part by modulating the activity of members of the miRNA regulatory pathway. Here, we highlight the vital role mutations in the miRNA core machinery play in promoting malignant transformation. Furthermore, we discuss how mutant KRAS can simultaneously impact multiple steps of miRNA processing and function to promote tumorigenesis. Although the ability of KRAS to hijack the miRNA regulatory pathway adds a layer of complexity to its oncogenic nature, it also provides a potential therapeutic avenue that has yet to be exploited in the clinic. Moreover, concurrent targeting of mutant KRAS and members of the miRNA core machinery represents a potential strategy for treating cancer.

DICER1 syndrome and embryonal rhabdomyosarcoma of the cervix: a case report and literature review

Background

Embryonal rhabdomyosarcomas (ERMS) of the uterine cervix and corpus are rare pediatric tumors usually associated with a late age of onset and frequent somatic DICER1 mutation. It may also develop in the context of a familial predisposition such as DICER1 syndrome requiring specific medical care for children and young adults at risk for a broad range of tumors.

Case presentation

This is a case of a prepubescent 9-year-old girl who was presented to our department for metrorrhagias due to a vaginal cervical mass, initially classified as a müllerian endocervical polyp on negative myogenin immunostaining. The patient subsequently manifested growth retardation (-2DS) and learning disabilities leading to genetic explorations and the identification of a germline pathogenic DICER1 variant. The family history revealed thyroid diseases in the father, aunt and paternal grandmother before the age of 20.

Conclusion

Rare tumors such as cervical ERMS associated with a family history of thyroid disease during infancy could be related to DICER1 syndrome. Identifying at-risk relatives is challenging but necessary to detect early DICER1 spectrum tumors in young patients.

Fetal Lung Interstitial Tumor (FLIT): Review of The Literature

Fetal lung interstitial tumor (FLIT) is an extremely rare pediatric lung tumor that shares radiological features with congenital pulmonary malformations (cPAM) and other lung neoplasms. A review of the literature, together with the first European case, are herein reported. A systematic and manual search of the literature using the keyword "fetal lung interstitial tumor" was conducted on PUBMED, Scopus, and SCIE (Web of Science). Following the PRISMA guidelines, 12 articles were retrieved which describe a total of 21 cases of FLIT, and a new European case is presented. A prenatal diagnosis was reported in only 3 out of 22 (13%) cases. The mean age at surgery was 31 days of life (1-150); a lobectomy was performed in most of the cases. No complications or recurrence of disease were reported at a mean follow-up of 49 months. FLIT is rarely diagnosed during pregnancy, may present at birth with different levels of respiratory distress, and requires prompt surgical resection. Histology and immunohistochemistry allow for the differentiation of FLIT from cPAM and other lung tumors with poor prognosis, such as pleuropulmonary blastoma, congenital peri-bronchial myofibroblastic tumor, inflammatory myofibroblastic tumor, and congenital or infantile fibrosarcoma.

Health-related quality of life in children and adolescents with pleuropulmonary blastoma: A report from the International PPB/DICER1 Registry

PURPOSE

Pleuropulmonary blastoma (PPB) is the most common lung cancer of infancy and early childhood and is associated with germline DICER1 variants. Type I and Ir PPB are cystic lesions treated surgically, with a subset of children with type I receiving chemotherapy. Type II and III are more aggressive lesions, treated with surgery, intensive chemotherapy and potentially radiation. We sought to assess health-related quality of life (HRQoL) in children with PPB and known germline DICER1 variants.

METHODS

Children with a diagnosis of PPB or germline DICER1 pathogenic variant without history of PPB or other DICER1-related neoplasm (DICER1+ only) were enrolled in the International PPB/DICER1 Registry. Parent reports for participants aged 2-17 years for the PedsQL v.4 and PedsQL Multidimensional Fatigue Scale v.3 were collected. Fatigue, physical, and psychosocial function scores were compared.

RESULTS

Analysis included 84 participants (PPB type Ir = 20, type I = 15, type II/III = 27, DICER1+ only = 22). Total fatigue scores of participants with type I and II/III PPB were lower compared to DICER1+ only, with effect size larger in type II/III (-0.82 vs. -0.40). Total psychosocial and physical functioning scores were lower in participants with type I and type II/III PPB compared to DICER1+ only, with larger effects noted in type II/III. Female sex was suggestive of worse HRQoL for both type I/Ir and type II/III cohorts.

CONCLUSIONS

These data demonstrate the importance of regular HRQoL assessment in patients with a history of PPB as well as the importance and feasibility of studying HRQoL in children with rare tumors.

Specifications of the ACMG/AMP Variant Classification Guidelines for Germline DICER1 Variant Curation

Germline pathogenic variants in DICER1 predispose individuals to develop a variety of benign and malignant tumors. Accurate variant curation and classification is essential for reliable diagnosis of DICER1-related tumor predisposition and identification of individuals who may benefit from surveillance. Since 2015, most labs have followed the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) sequence variant classification guidelines for DICER1 germline variant curation. However, these general guidelines lack gene-specific nuances and leave room for subjectivity. Consequently, a group of DICER1 experts joined ClinGen to form the DICER1 and miRNA-Processing Genes Variant Curation Expert Panel (VCEP), to create DICER1- specific ACMG/AMP guidelines for germline variant curation. The VCEP followed the FDA-approved ClinGen protocol for adapting and piloting these guidelines. A diverse set of 40 DICER1 variants were selected for piloting, including 14 known Pathogenic/Likely Pathogenic (P/LP) variants, 12 known Benign/Likely Benign (B/LB) variants, and 14 variants classified as variants of uncertain significance (VUS) or with conflicting interpretations in ClinVar. Clinically meaningful classifications (i.e., P, LP, LB, or B) were achieved for 82.5% (33/40) of the pilot variants, with 100% concordance among the known P/LP and known B/LB variants. Half of the VUS or conflicting variants were resolved with four variants classified as LB and three as LP. These results demonstrate that the DICER1-specific guidelines for germline variant curation effectively classify known pathogenic and benign variants while reducing the frequency of uncertain classifications. Individuals and labs curating DICER1 variants should consider adopting this classification framework to encourage consistency and improve objectivity.

Genomic characterization of DICER1-associated neoplasms uncovers molecular classes

DICER1 syndrome is a tumor predisposition syndrome that is associated with up to 30 different neoplastic lesions, usually affecting children and adolescents. Here we identify a group of mesenchymal tumors which is highly associated with DICER1 syndrome, and molecularly distinct from other DICER1-associated tumors. This group of DICER1-associated mesenchymal tumors encompasses multiple well-established clinicopathological tumor entities and can be further divided into three clinically meaningful classes designated "low-grade mesenchymal tumor with DICER1 alteration" (LGMT DICER1), "sarcoma with DICER1 alteration" (SARC DICER1), and primary intracranial sarcoma with DICER1 alteration (PIS DICER1). Our study not only provides a combined approach to classify DICER1-associated neoplasms for improved clinical management but also suggests a role for global hypomethylation and other recurrent molecular events in sarcomatous differentiation in mesenchymal tumors with DICER1 alteration. Our results will facilitate future investigations into prognostication and therapeutic approaches for affected patients.

Targeting Mutant Dicer Tumorigenesis in Pleuropulmonary Blastoma via Inhibition of RNA Polymerase I

DICER1 mutations predispose to increased risk for various cancers, particularly pleuropulmonary blastoma (PPB), the commonest lung malignancy of childhood. There is a paucity of directly actionable molecular targets as these tumors are driven by loss-of-function mutations of DICER1. Therapeutic development for PPB is further limited by a lack of biologically and physiologically-representative disease models. Given recent evidence of Dicer's role as a haploinsufficient tumor suppressor regulating RNA polymerase I (Pol I), Pol I inhibition could abrogate mutant Dicer-mediated accumulation of stalled polymerases to trigger apoptosis. Hence, we developed a novel sub-pleural orthotopic PPB patient-derived xenograft (PDX) model that retained both RNase IIIa and IIIb hotspot mutations and recapitulated the cardiorespiratory physiology of intra-thoracic disease, and with it evaluated the tolerability and efficacy of first-in-class Pol I inhibitor CX-5461. In PDX tumors, CX-5461 significantly reduced H3K9 di-methylation and increased nuclear p53 expression, within 24 hours' exposure. Following treatment at the maximum tolerated dosing regimen (12 doses, 30mg/kg), tumors were smaller and less hemorrhagic than controls, with significantly decreased cellular proliferation, and increased apoptosis. As demonstrated in a novel intra-thoracic tumor model of PPB, Pol I inhibition with CX-5461 could be a tolerable and clinically-feasible therapeutic strategy for mutant Dicer tumors, inducing anti-tumor effects by decreasing H3K9 methylation and enhancing p53-mediated apoptosis.

From Malignant Thyroid Teratoma to Thyroblastoma: Evolution of a Newly-recognized DICER1 -associated Malignancy

Thyroblastoma is a novel thyroid malignancy included in the 5th Edition WHO Classification of Endocrine and Neuroendocrine Tumours. The majority of tumors now classified as thyroblastoma were originally regarded to be malignant thyroid teratomas. However, these neoplasms were recently recognized as a separate entity based on a distinctive constellation of primitive multilineage elements, including immature thyroid epithelium, undifferentiated or rhabdomyoblastic spindle cell proliferations, and neuroepithelial blastema, as well as recurrent DICER1 hotspot mutations. Thyroblastoma is an aggressive tumor that leads to death from disease in ~50% of patients, making it essential to differentiate this entity from a wide range of other thyroid tumors that show overlapping histologic features or DICER1 mutations. This review aims to provide a practical overview of the background, clinicopathologic features, molecular underpinnings, and differential diagnosis of this recently-described and molecularly-defined entity.

On the Chopping Block: Overview of DICER1 Mutations in Endocrine and Neuroendocrine Neoplasms

Mutational inactivation of the DICER1 gene causes aberrant micro-RNA maturation, which in turn may have consequences for the posttranscriptional regulation of gene expression, thereby contributing to tumor formation in various organs. Germline DICER1 mutations cause DICER1 syndrome, a pleiotropic condition with an increased risk of various neoplastic conditions in the pleura, ovaries, thyroid, pituitary, pineal gland, and mesenchymal tissues. Somatic DICER1 mutations are also frequently observed in a wide variety of solid tumors, thereby highlighting the importance of this gene in tumor development. In this review, the importance of DICER1 inactivation in endocrine tumors is discussed.

Structure of the human DICER-pre-miRNA complex in a dicing state

Dicer has a key role in small RNA biogenesis, processing double-stranded RNAs (dsRNAs)^1,2. Human DICER (hDICER, also known as DICER1) is specialized for cleaving small hairpin structures such as precursor microRNAs (pre-miRNAs) and has limited activity towards long dsRNAs-unlike its homologues in lower eukaryotes and plants, which cleave long dsRNAs. Although the mechanism by which long dsRNAs are cleaved has been well documented, our understanding of pre-miRNA processing is incomplete because structures of hDICER in a catalytic state are lacking. Here we report the cryo-electron microscopy structure of hDICER bound to pre-miRNA in a dicing state and uncover the structural basis of pre-miRNA processing. hDICER undergoes large conformational changes to attain the active state. The helicase domain becomes flexible, which allows the binding of pre-miRNA to the catalytic valley. The double-stranded RNA-binding domain relocates and anchors pre-miRNA in a specific position through both sequence-independent and sequence-specific recognition of the newly identified 'GYM motif'³. The DICER-specific PAZ helix is also reoriented to accommodate the RNA. Furthermore, our structure identifies a configuration of the 5' end of pre-miRNA inserted into a basic pocket. In this pocket, a group of arginine residues recognize the 5' terminal base (disfavouring guanine) and terminal monophosphate; this explains the specificity of hDICER and how it determines the cleavage site. We identify cancer-associated mutations in the 5' pocket residues that impair miRNA biogenesis. Our study reveals how hDICER recognizes pre-miRNAs with stringent specificity and enables a mechanistic understanding of hDICER-related diseases.

Challenges in DICER1-Associated Lung Disease

Pleuropulmonary blastoma (PPB) is a tumor occurring almost exclusively in infants and young children. This is the most common primary-lung malignancy in childhood. There is age-associated progression through a distinctive sequence of pathologic changes, from a purely multicystic lesion type I to a high-grade sarcoma type II and III. While complete resection is the cornerstone treatment for type I PPB, aggressive chemotherapy with a less favorable prognosis is associated with type II and III. DICER1 germline mutation is positive in 70% of children with PPB. Diagnosis is challenging, as it resembles congenital pulmonary airway malformation (CPAM) in imaging. Although PPB is an extremely rare malignancy, over the past five years we have encountered several children diagnosed with PPB in our medical center. Herein, we present some of these children and discuss diagnostic, ethical, and therapeutic challenges.

miRNA biogenesis and inherited disorders: clinico-molecular insights

MicroRNAs (miRNAs) play vital roles in the regulation of gene expression, a process known as miRNA-induced gene silencing. The human genome codes for many miRNAs, and their biogenesis relies on a handful of genes, including DROSHA, DGCR8, DICER1, and AGO1/2. Germline pathogenic variants (GPVs) in these genes cause at least three distinct genetic syndromes, with clinical manifestations that range from hyperplastic/neoplastic entities to neurodevelopmental disorders (NDDs). Over the past decade, DICER1 GPVs have been shown to lead to tumor predisposition. Moreover, recent findings have provided insight into the clinical consequences arising from GPVs in DGCR8, AGO1, and AGO2. Here we provide a timely update with respect to how GPVs in miRNA biogenesis genes alter miRNA biology and ultimately lead to their clinical manifestations.

Hereditary cancer syndromes

Hereditary cancer syndromes (HCSs) are arguably the most frequent category of Mendelian genetic diseases, as at least 2% of presumably healthy subjects carry highly-penetrant tumor-predisposing pathogenic variants (PVs). Hereditary breast-ovarian cancer and Lynch syndrome make the highest contribution to cancer morbidity; in addition, there are several dozen less frequent types of familial tumors. The development of the majority albeit not all hereditary malignancies involves two-hit mechanism, i.e. the somatic inactivation of the remaining copy of the affected gene. Earlier studies on cancer families suggested nearly fatal penetrance for the majority of HCS genes; however, population-based investigations and especially large-scale next-generation sequencing data sets demonstrate that the presence of some highly-penetrant PVs is often compatible with healthy status. Hereditary cancer research initially focused mainly on cancer detection and prevention. Recent studies identified multiple HCS-specific drug vulnerabilities, which translated into the development of highly efficient therapeutic options.

Type I and Ir pleuropulmonary blastoma (PPB): A report from the International PPB/DICER1 Registry

BACKGROUND

Pleuropulmonary blastoma (PPB) is the most common lung cancer of infancy and early childhood. Type I PPB is a purely cystic lesion that has a microscopic population of primitive small cells with or without rhabdomyoblastic features and may progress to type II or III PPB, whereas type Ir lacks primitive small cells.

METHODS

Children with suspected PPB were enrolled in the International PPB/DICER1 Registry. Pathology was centrally reviewed, and follow-up was ascertained annually.

RESULTS

Between 2006 and 2022, 205 children had centrally reviewed type I or Ir PPB; 39% of children with type I and 5% of children with type Ir PPB received chemotherapy. Outcomes were favorable, although 11 children (nine with type I and two with type Ir PPB) experienced progression to type II/III (n = 8) or regrowth of type I PPB at the surgical site (n = 3), none of whom received chemotherapy before progression. Age and cyst size in combination were more suitable than either factor alone in predicting whether a particular lesion was type I or Ir PPB.

CONCLUSIONS

For young children with type I PPB, outcomes are favorable, but complete resection is indicated because of the risk for progression. Chemotherapy may be useful in a subset of children at increased risk for recurrence/progression. Efforts to risk stratify children with type I PPB to optimize outcomes while reducing treatment-related side effects are underway.

Outcomes for Children With Type II and Type III Pleuropulmonary Blastoma Following Chemotherapy: A Report From the International PPB/DICER1 Registry

PURPOSE

Pleuropulmonary blastoma (PPB) is the most common primary lung neoplasm of infancy and early childhood. Type II and type III PPB have historically been associated with a poor prognosis.

METHODS

Patients with known or suspected PPB were enrolled in the International PPB/DICER1 Registry. Medical records were abstracted with follow-up ascertained annually. All PPB diagnoses were confirmed by central pathology review. Beginning in 2007, the IVADo regimen (ifosfamide, vincristine, actinomycin-D, and doxorubicin) was recommended as a potential treatment regimen for children with type II and type III PPB. This regimen was compared with a historical control cohort.

RESULTS

From 1987 to 2021, 314 children with centrally confirmed type II and type III PPB who received upfront chemotherapy were enrolled; 132 children (75 with type II and 57 with type III) received IVADo chemotherapy. Adjusted analyses suggest improved overall survival for children treated with IVADo in comparison with historical controls with an estimated hazard ratio of 0.65 (95% CI, 0.39 to 1.08). Compared with localized disease, distant metastasis at diagnosis was associated with worse PPB event-free survival and overall survival with hazard ratio of 4.23 (95% CI, 2.42 to 7.38) and 4.69 (95% CI, 2.50 to 8.80), respectively.

CONCLUSION

The use of IVADo in children with type II and type III PPB resulted in similar-to-improved outcomes compared with historical controls. Inferior outcomes with metastatic disease suggest the need for novel therapies. This large cohort of uniformly treated children with advanced PPB serves as a benchmark for future multicenter therapeutic studies for this rare pediatric tumor.

All pineal tumors expressing germ cell tumor markers are not necessarily germ cell tumors: histopathological and molecular study of a midline primary intracranial sarcoma DICER1-mutant

Primary intracranial sarcoma DICER1-mutant is a rare and newly recognized tumor type introduced in the 2021 WHO Classification of Central Nervous System Tumors. It is defined as a spindle cell sarcoma dysplaying eosinophilic intracytoplasmic globules, myogenic differentiation, and DICER1 gene mutation, either somatic or germline. Most reported cases were hemispheric except one, recently described in the pineal region. Here, we report the case of a 12 year-old boy with a pineally located tumor. Despite midline location, poorly differenciated morphology and germ cell marker expression, the association of DICER1 and NF1 hotspot mutations and a specific DNA methylation signature finally lead to the diagnosis of primary intracranial sarcoma DICER1-mutant instead of germ cell tumor. Furthermore, our molecular exploratory results involved a pathway, which was not previously evidenced in those DICER1 mutated cerebral sarcoma that is the canonical Wnt signaling driving likely a part of oncogenesis in this newly described pineal entity.

Comprehensive Molecular Profiling of Sinonasal Teratocarcinosarcoma Highlights Recurrent SMARCA4 Inactivation and CTNNB1 Mutations

Sinonasal teratocarcinosarcoma (TCS) is a rare tumor defined by intermixed neuroepithelial, mesenchymal, and epithelial elements. While its etiology was historically ambiguous, we recently reported frequent SMARCA4 loss by immunohistochemistry, suggesting that TCS might be related to SMARCA4-deficient sinonasal carcinomas. However, other molecular alterations including CTNNB1 mutation have been reported in TCS, and its full genetic underpinnings are unclear. Here, we performed the first comprehensive molecular analysis of sinonasal TCS to better understand its pathogenesis and classification. We collected 30 TCS including 22 cases from our initial study. Immunohistochemical loss of SMARCA4 was seen in 22 cases (73%), with total loss in 18 cases (60%). β-catenin showed nuclear localization in 14 cases (64%) of the subset tested. We selected 17 TCS for next-generation sequencing with enrichment for partial or intact SMARCA4 immunoexpression. We identified inactivating SMARCA4 mutations in 11 cases (65%) and activating CTNNB1 mutations in 6 cases (35%), including 5 cases with both. Of 5 cases that lacked SMARCA4 or CTNNB1 mutation, 2 harbored other SWI/SNF complex and Wnt pathway alterations, including 1 with SMARCB1 inactivation and 1 with concomitant APC and ARID1A mutations, and 3 had other findings, including DICER1 hotspot mutation. These findings confirm that SMARCA4 inactivation is the dominant genetic event in sinonasal TCS with frequent simultaneous CTNNB1 mutations. They further underscore a possible relationship between TCS and sinonasal carcinomas with neuroendocrine/neuroectodermal differentiation. However, while SMARCA4 and β-catenin immunohistochemistry may help confirm a challenging diagnosis, TCS should not be regarded as a molecularly defined entity.

Splicing-Disrupting Mutations in Inherited Predisposition to Solid Pediatric Cancer

The prevalence of hereditary cancer in children was estimated to be very low until recent studies suggested that at least 10% of pediatric cancer patients carry a germline mutation in a cancer predisposition gene. A significant proportion of pathogenic variants associated with an increased risk of hereditary cancer are variants affecting splicing. RNA splicing is an essential process involved in different cellular processes such as proliferation, survival, and differentiation, and alterations in this pathway have been implicated in many human cancers. Hereditary cancer genes are highly susceptible to splicing mutations, and among them there are several genes that may contribute to pediatric solid tumors when mutated in the germline. In this review, we have focused on the analysis of germline splicing-disrupting mutations found in pediatric solid tumors, as the discovery of pathogenic splice variants in pediatric cancer is a growing field for the development of personalized therapies. Therapies developed to correct aberrant splicing in cancer are also discussed as well as the options to improve the diagnostic yield based on the increase in the knowledge in splicing.

Congenital lung malformations: Dysregulated lung developmental processes and altered signaling pathways

Congenital lung malformations comprise a diverse group of anomalies including congenital pulmonary airway malformation (CPAM, previously known as congenital cystic adenomatoid malformation or CCAM), bronchopulmonary sequestration (BPS), congenital lobar emphysema (CLE), bronchogenic cysts, and hybrid lesions. Little is known about the signaling pathways that underlie the pathophysiology of these lesions and the processes that may promote their malignant transformation. In the last decade, the use of transgenic/knockout animal models and the implementation of next generation sequencing on surgical lung specimens have increased our knowledge on the pathophysiology of these lesions. Herein, we provide an overview of normal lung development in humans and rodents, and we discuss the current state of knowledge on the pathophysiology and molecular pathways that are altered in each congenital lung malformation.

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 >40% in 25% of cases (2 of 8) and >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.

Proteomic methods identified P75 as marker of poor prognosis in pleuropulmonary blastoma

OBJECTIVES

To study the causes of the rapid progression of pleuropulmonary blastoma and to identify molecular markers related to its prognosis.

MATERIALS AND METHODS

Three pairs of fresh frozen samples of pleuropulmonary blastoma tumors and adjacent normal tissues were analyzed for proteomics, focusing on the protein molecules with significantly increased expression in tumor tissues and related to the cell cycle and DNA replication. The top five protein molecules were selected and verified by immunohistochemistry. To analyze the correlation between the expression of verified protein molecules in pleuropulmonary blastoma and early recurrence/metastasis of pleuropulmonary blastoma.

RESULTS

Compared with the adjacent normal tissues, 1759 proteins were upregulated and 967 proteins were downregulated in pleuropulmonary blastoma. The top five proteins related to the cell cycle and DNA replication were ORC2, P75, Skp2, MCM4 and PCNA. However, only P75, MCM4 and PCNA were upregulated in pleuropulmonary blastoma as determined by immunohistochemistry. Further analysis showed that the expression of P75 in the recurrence/metastasis group was significantly higher than that in the no recurrence/metastasis group, while the expression of MCM4 and PCNA was not significantly different between the recurrence/metastasis group and the no recurrence/metastasis group.

CONCLUSIONS

MCM4, PCNA and P75 may all play an important role in the progression of pleuropulmonary blastoma. Among them, P75 is related to the prognosis and may be used as a marker to predict the prognosis of pleuropulmonary blastoma.

A systematic review of the clinicopathological features and prognostic outcomes of DICER1-mutant malignant brain neoplasms

OBJECTIVE

DICER1-mutant malignant brain neoplasms are very rare tumors, and published data have relied on case reports or small case series. In this review, the authors aimed to systematically summarize the types and distribution patterns of DICER1 mutations, clinicopathological characteristics, and prognostic outcomes of these tumors.

METHODS

The authors searched PubMed and Web of Science for relevant studies. They included studies if they provided individual patient data of primary malignant brain tumors carrying DICER1 mutations.

RESULTS

The authors found 16 studies consisting of 9 embryonal tumors with multilayered rosettes (ETMRs), 30 pineoblastomas, 52 primary intracranial sarcomas, and 27 pituitary blastomas. Pineoblastoma, ETMR, and pituitary blastoma were more likely to carry DICER1 germline mutations, while only a small subset of primary intracranial sarcomas harbored these mutations (p < 0.001). Nearly 80% of tumors with germline mutations also had another somatic mutation in DICER1. ETMR and primary intracranial sarcoma were associated with an increased risk for tumor progression and relapse compared with pituitary blastoma and pineoblastoma (p = 0.0025), but overall survival (OS) was not significantly different. Gross-total resection (GTR) and radiotherapy administration were associated with prolonged OS.

CONCLUSIONS

ETMR, pineoblastoma, primary intracranial sarcoma, and pituitary blastoma should be considered rare phenotypes of the DICER1 syndrome, and families should be counseled and screened for associated tumors. ETMR and primary intracranial sarcoma had a higher risk of relapse. GTR and radiotherapy appeared to improve the OS of patients with DICER1-mutant malignant intracranial tumors.

DICER1-associated Tumors in the Female Genital Tract: Molecular Basis, Clinicopathologic Features, and Differential Diagnosis

DICER1 syndrome is a tumor predisposition syndrome in which patients are at an increased risk of developing a wide variety of benign and malignant neoplasms with a hallmark constellation of pediatric pleuropulmonary blastoma, cystic nephroma, and thyroid lesions. DICER1 encodes an RNA endoribonuclease that is crucial to the processing of microRNA and may play a role in the maturation of Müllerian tissue. Within the gynecologic tract, germline mutations in DICER1 are associated with an array of rare tumors, including Sertoli-Leydig cell tumor, embryonal rhabdomyosarcoma of the cervix, gynandroblastoma, and juvenile granulosa cell tumor, which typically present in childhood, adolescence, or early adulthood. In addition, somatic DICER1 mutations have been described in rare gynecologic tumors such as adenosarcoma, Sertoli cell tumor, ovarian fibrosarcoma, cervical primitive neuroectodermal tumor, carcinosarcoma, and germ cell tumors. In light of the significant association with multiple neoplasms, genetic counseling should be considered for patients who present with a personal or family history of these rare DICER1-associated gynecologic tumors. This review highlights the most current understanding of DICER1 genetic alterations and describes the clinical, histopathologic, and immunohistochemical features and differential diagnoses for gynecologic tumors associated with DICER1 mutation.

Panoramic view of microRNAs in regulating cancer stem cells

Cancer stem cells (CSCs) are a subgroup of tumor cells, possessing the abilities of self-renewal and generation of heterogeneous tumor cell lineages. They are believed to be responsible for tumor initiation, metastasis, as well as chemoresistance in human malignancies. MicroRNAs (miRNAs) are small noncoding RNAs that play essential roles in various cellular activities including CSC initiation and CSC-related properties. Mature miRNAs with ∼22 nucleotides in length are generated from primary miRNAs via its precursors by miRNA-processing machinery. Extensive studies have demonstrated that mature miRNAs modulate CSC initiation and stemness features by regulating multiple pathways and targeting stemness-related factors. Meanwhile, both miRNA precursors and miRNA-processing machinery can also affect CSC properties, unveiling a new insight into miRNA function. The present review summarizes the roles of mature miRNAs, miRNA precursors, and miRNA-processing machinery in regulating CSC properties with a specific focus on the related molecular mechanisms, and also outlines the potential application of miRNAs in cancer diagnosis, predicting prognosis, as well as clinical therapy.

Congenital midline spinal hamartoma in an infant with DICER1 syndrome: A case report

Congenital spinal hamartomas are rare benign tumors. They are mostly seen in infants and are typically asymptomatic at presentation. Spinal hamartomas have not been associated with any known cancer predisposition syndrome. DICER1 syndrome is a well-characterized cancer predisposition syndrome caused by a germline mutation in the DICER1 gene, which shows variable expressivity. To our knowledge, spinal hamartoma has never been described in individuals with DICER1 syndrome. Here, we describe a rare association of congenital spinal hamartoma and DICER1 syndrome in a 5-week-old infant, with molecular findings suggestive of the implication of DICER1 in the pathogenesis of this tumor.

PUMILIO competes with AUF1 to control DICER1 RNA levels and miRNA processing

DICER1 syndrome is a cancer pre-disposition disorder caused by mutations that disrupt the function of DICER1 in miRNA processing. Studying the molecular, cellular and oncogenic effects of these mutations can reveal novel mechanisms that control cell homeostasis and tumor biology. Here, we conduct the first analysis of pathogenic DICER1 syndrome allele from the DICER1 3'UTR. We find that the DICER1 syndrome allele, rs1252940486, abolishes interaction with the PUMILIO RNA binding protein with the DICER1 3'UTR, resulting in the degradation of the DICER1 mRNA by AUF1. This single mutational event leads to diminished DICER1 mRNA and protein levels, and widespread reprogramming of miRNA networks. The in-depth characterization of the rs1252940486 DICER1 allele, reveals important post-transcriptional regulatory events that control DICER1 levels.

A primary DICER1-sarcoma with KRAS and TP53 mutations in a child with suspected ECCL

A child had been followed since infancy by our multi-disciplinary neuro-oncology clinic with annual magnetic resonance imaging (MRI) under the presumed diagnosis of encephalocraniocutaneous lipomatosis (ECCL), with clinical features including nevus psiloliparus, scalp lipoma, nodular skin tag on and coloboma of the eyelid, cortical atrophy and meningeal angiomatosis. At the age of 4, she was found to have a large temporoparietal lesion causing elevated intracranial pressure requiring surgical resection. Histopathological exam of the tumor was suggestive of an intracranial sarcoma. Sequencing analysis of the tumor revealed mutations in DICER1, KRAS and TP53. Subsequent germline testing confirmed DICER1 syndrome and revealed an insignificant FGFR1 variant at a low frequency. Methylation profile of the tumor showed the tumor clustered most closely with sarcoma (rhabdomyosarcoma-like), confirming this tumor to be a primary DICER1-sarcoma. Compared to the previously reported cases, our unique case of primary DICER1-sarcoma also demonstrated neurofilament and chromogranin positivity, and genomic instability with loss of chromosome 4p, 4q, 8p, 11p, and 19p, as well as gains in chromosome 7p, 9p, 9q, 13q, and 15q on copy variant analysis. The detailed sequencing and methylation information discovered in this unique case of DICER1-sarcoma will hopefully help further our understanding of this rare and emerging entity.

Update on Ovarian Sex Cord-Stromal Tumors

This article focuses on the recent advances in ovarian sex cord-stromal tumors, predominantly in the setting of their molecular underpinnings. The integration of genetic information with morphologic and immunohistochemical findings in this rare subset of tumors is of clinical significance from refining the diagnostic and prognostic stratifications to genetic counseling.

DICER1-associated hepatic cystic neoplasm with pleuropulmonary blastoma-like features: a novel clinicopathologic diagnosis

This report documents a unique multicystic neoplasm of the liver in an 8-month-old boy with a heterozygous germline pathogenic DICER1 variant. This neoplasm, initially considered most likely a mesenchymal hamartoma based on imaging, demonstrated the characteristic histologic pattern of embryonal rhabdomyosarcoma residing in the subepithelial or cambium layer-like zone of the epithelial-lined cysts. Thus, although the differential diagnosis includes mesenchymal hamartoma, a young child with a multicystic mass lesion in the liver, lung, or kidney should both raise the possibility of a germline pathogenic DICER1 variant and also not be mistaken for one of the other hepatic neoplasms of childhood.

PRAME protein expression in DICER1-related tumours

DICER1 syndrome is an autosomal dominant tumour predisposition syndrome usually affecting persons under 30 years of age. Many of the associated benign and malignant lesions occur almost exclusively in DICER1 syndrome. One such tumour, pituitary blastoma (pitB), overexpresses PRAME 500x above control levels. PRAME (PReferentially expressed Antigen in MElanoma) is expressed in malignancies that are not DICER1-related (e.g. melanoma). To address whether PRAME expression is part of the DICER1 phenotype, or simply a feature of pitB, a series of 75 DICER1-mutated specimens and 33 non-mutated specimens was surveyed using immunohistochemistry for PRAME, together with EZH2, which complexes with PRAME. In DICER1-mutated specimens, positive staining for PRAME was only seen in malignant tumours; 7 of 11 histological types and 34/62 individual tumours were positive, while non-tumourous lesions were always negative. Pleuropulmonary blastoma (PPB) showed a continuum in staining, with type I lesions being PRAME negative (n = 7) but all type II and type III lesions PRAME positive (n = 7). Similarly, cystic nephroma (CN) was negative (n = 8), with anaplastic sarcoma of the kidney being positive (n = 2). However, one atypical CN with mesenchymal cell proliferation was PRAME-positive. Embryonal rhabdomyosarcoma (RMS) with DICER1 pathogenic variants (PVs) was positive for PRAME (5/6), but the same tumour type without DICER1 PVs was also positive (9/15). Staining for EZH2 corresponded to that seen with PRAME, validating the latter. This study leads us to conclude that (1) PRAME expression occurs in two-thirds of DICER1-related malignancies; (2) PRAME may be a marker for the progression that certain DICER1-related lesions are thought to undergo, such as PPB and CN; and (3) PRAME expression in some tumours, such as RMS, appears to be an intrinsic feature of the tumour, rather than specifically related to DICER1 PVs. Therapy directed against PRAME may offer novel treatment options in patients with the DICER1 syndrome.

DICER1 mutations in primary central nervous system tumors: new insights into histologies, mutations, and prognosis

PURPOSE

We sought to characterize clinical outcomes for adult and pediatric patients with primary CNS tumors harboring DICER1 mutations or loss of DICER1.

METHODS

We conducted a retrospective cohort study of 98 patients who were treated between 1995 and 2020 for primary CNS tumors containing DICER1 mutations or loss of DICER1 on chromosome 14q, identified by targeted next generation sequencing. Kaplan-Meier plots and log rank tests were used to analyze survival. Cox proportional-hazards model was used for univariate and multivariable analyses for all-cause mortality (ACM).

RESULTS

Within our cohort, the most common malignancies were grade 3/4 glioma (61%), grade 1/2 glioma (17%), and CNS sarcoma (6%). Sarcoma and non-glioma histologies, and tumors with biallelic DICER1 mutations or deletions were common in the pediatric population. Mutations occurred throughout DICER1, including missense mutations in the DexD/H-box helicase, DUF283, RNaseIIIa, and RNaseIIIb domains. For patients with grade 3/4 glioma, MGMT methylation (Hazard ratio [HR] 0.35, 95% Confidence Interval [CI] 0.16-0.73, p = 0.005), IDH1 R132 mutation (HR 0.11, 95% CI 0.03-0.41, p = 0.001), and missense mutation in the DexD/H-box helicase domain (HR 0.06, 95% CI 0.01-0.38, p = 0.003) were independently associated with longer time to ACM on multivariable analyses.

CONCLUSION

DICER1 mutations or loss of DICER1 occur in diverse primary CNS tumors, including previously unrecognized grade 3/4 gliomas as the most common histology. While prior studies have described RNaseIIIb hotspot mutations, we document novel mutations in additional DICER1 functional domains. Within the grade 3/4 glioma cohort, missense mutation in the DexD/H-box helicase domain was associated with prolonged survival.

ADP-Ribosylation Post-Translational Modification: An Overview with a Focus on RNA Biology and New Pharmacological Perspectives

Cellular functions are regulated through the gene expression program by the transcription of new messenger RNAs (mRNAs), alternative RNA splicing, and protein synthesis. To this end, the post-translational modifications (PTMs) of proteins add another layer of complexity, creating a continuously fine-tuned regulatory network. ADP-ribosylation (ADPr) is an ancient reversible modification of cellular macromolecules, regulating a multitude of key functional processes as diverse as DNA damage repair (DDR), transcriptional regulation, intracellular transport, immune and stress responses, and cell survival. Additionally, due to the emerging role of ADP-ribosylation in pathological processes, ADP-ribosyltransferases (ARTs), the enzymes involved in ADPr, are attracting growing interest as new drug targets. In this review, an overview of human ARTs and their related biological functions is provided, mainly focusing on the regulation of ADP-ribosyltransferase Diphtheria toxin-like enzymes (ARTD)-dependent RNA functions. Finally, in order to unravel novel gene functional relationships, we propose the analysis of an inventory of human gene clusters, including ARTDs, which share conserved sequences at 3′ untranslated regions (UTRs).

Proceedings of the North American Society of Head and Neck Pathology, Los Angeles, CA, March 20, 2022: DICER1-Related Thyroid Tumors

DICER1 syndrome is an autosomal dominant tumor predisposition syndrome caused by germline DICER1 mutations. In the thyroid, DICER1 syndrome is associated with early-onset multinodular goiter and thyroid carcinomas. Subsequent studies have shown that somatic DICER1 mutations, though rare, can occur in follicular-patterned thyroid tumors, such as follicular adenomas and follicular thyroid carcinomas, with a higher rate seen in pediatric follicular thyroid carcinomas and in follicular thyroid carcinomas with a macrofollicular architecture. Somatic DICER1 mutations have also been reported in pediatric papillary thyroid carcinomas lacking other alterations typically associated with thyroid tumorigenesis. Although thyroid carcinomas with underlying DICER1 mutations are usually indolent, recent studies have shown that pediatric poorly differentiated thyroid carcinoma and thyroblastoma, both aggressive tumors, also harbor DICER1 mutations. This review will discuss mechanisms of DICER1 tumorigenesis and describe thyroid tumors associated with germline and somatic DICER1 mutations.