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

The Histological Spectrum of DICER1-Associated Neoplasms

DICER1 syndrome is a heterogeneous cancer predisposition syndrome, characterized by a large variety of benign and malignant tumor types, and caused by germline heterozygous pathogenic variants in the DICER1 gene, which is essential in miRNA processing and RNA interference. The clinical manifestations are diverse, with pleuropulmonary blastoma, Sertoli-Leydig cell tumor, cystic nephroma, uterine cervical embryonal rhabdomyosarcoma, and thyroid follicular nodular disease being the most prevalent tumor types. Since these neoplasms are rare and particularly occur in the pediatric population, pathologists should be aware of the potential relationship of these tumors with an underlying DICER1 syndrome in order to perform or suggest additional molecular pathologic analysis and refer patients and their parents for genetic counseling and testing. This review describes the various DICER1-related tumor types with emphasis on the histological features, reflects on the molecular pathogenesis of DICER1, and aims to raise awareness of this syndrome to facilitate earlier diagnosis.

Pleuropulmonary blastoma and DICER1-related tumor predisposition: from clinicopathologic observations to clinical trial

PURPOSE OF REVIEW

Pleuropulmonary blastoma (PPB) is a rare primary lung neoplasm of infancy and childhood. The purpose of this review is to highlight recent developments in our understanding of PPB and research strategies to facilitate future rare cancer research.

RECENT FINDINGS

The International PPB/DICER1 Registry has recently assembled the largest-ever cohorts of type I and Ir PPB and type II and III PPB. These analyses were strengthened by robust histologic, genetic and longitudinal data made possible by systematic data collection and abstraction and dedicated central pathology review. These cohorts have laid the groundwork for a prospective consortium-based clinical trial to assess response to camptothecins in type II and III PPB and standardize the use of chemotherapy in type I PPB.

SUMMARY

Significant strides in the study of PPB have been made through clinical, laboratory and translational research, multidisciplinary collaborations and the generous contributions of patients, families and referring physicians. Ongoing advancements will continue to depend on multidisciplinary, multiperspective global collaborations.

Rhabdomyosarcoma in children and young adults

Rhabdomyosarcoma (RMS) is the most common soft tissue malignancy in childhood, accounting for 3% of all pediatric malignancies and 50% of all pediatric soft tissue sarcomas. In adolescents and young adults (AYA) however, RMS comprises only 6.5% of all soft tissue sarcomas. Historically, diagnosis and treatment of RMS was based on histologic recognition of the alveolar subtype, which was associated with a worse prognosis. Within the past 20 years, the biologic characteristics of RMS have become clearer, with canonical fusion drivers, PAX3/7::FOXO1, characterizing the alveolar subtype (ARMS) and in turn associated with poor outcome, while chromosomal gains/losses in addition to RAS pathway alterations characterize the embryonal subtype (ERMS). Accordingly, detection of a FOXO1 gene fusion has become a commonplace diagnostic and prognostic tool allowing tumors to be treated based on presence or absence of a FOXO1 gene fusion. However, these cytogenetic and molecular alterations represent only a portion of the molecular landscape found in RMS, and other alterations are found with increasing frequency in various subsets of RMS. Clinical trials basing risk stratification on the presence or absence of the canonical PAX3/7::FOXO1 fusions have had success in identifying the poor responders. Due to poor outcomes, the presence of MYOD1 and TP53 alterations which are common in spindle cell sclerosing RMS (SSRMS) and RMS with anaplasia have also been integrated into trial risk stratification. Therefore, complete histologic and immunophenotypic characterization remain important to better recognize and study these rare subsets of RMS. This article will discuss the challenges of RMS classification including how to combine morphologic, immunophenotypic and molecular data to arrive at an integrated diagnosis. The use of newer techniques such as liquid biopsy and methylation profiling, will also continue to shape the classification of RMS and may further refine risk stratification and prognosis.

Liver-specific DICER1 syndrome model mice develop cystic liver tumors with defective primary cilia

DICER1 syndrome is a tumor predisposition syndrome caused by familial genetic mutations in DICER1. Pathogenic variants of DICER1 have been discovered in many rare cancers, including cystic liver tumors. However, the molecular mechanisms underlying liver lesions induced by these variants remain unclear. In the present study, we sought to gain a better understanding of the pathogenesis of these variants by generating a mouse model of liver-specific DICER1 syndrome. The mouse model developed bile duct hyperplasia with fibrosis, similar to congenital hepatic fibrosis, as well as cystic liver tumors resembling those in Caroli's syndrome, intrahepatic cholangiocarcinoma, and hepatocellular carcinoma. Interestingly, the mouse model of DICER1 syndrome showed abnormal formation of primary cilia in the bile duct epithelium, which is a known cause of bile duct hyperplasia and cyst formation. These results indicated that DICER1 mutations contribute to cystic liver tumors by inducing defective primary cilia. The mouse model generated in this study will be useful for elucidating the potential mechanisms of tumorigenesis induced by DICER1 variants and for obtaining a comprehensive understanding of DICER1 syndrome. © 2024 The Pathological Society of Great Britain and Ireland.

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.