Decoding the molecular heterogeneity of pediatric monomorphic post-solid organ transplant lymphoproliferative disorders.

Posttransplant lymphoproliferative disorders (PTLDs) represent a broad spectrum of lymphoid proliferations, frequently associated with Epstein-Barr virus (EBV) infection. The molecular profile of pediatric monomorphic PTLDs (mPTLDs) has not been elucidated, and it is unknown whether they display similar genetic features as their counterpart in adult and immunocompetent (IMC) pediatric patients. In this study, we investigated 31 cases of pediatric mPTLD after solid organ transplantation, including 24 diffuse large B-cell lymphomas (DLBCLs), mostly classified as activated B cell, and 7 cases of Burkitt lymphoma (BL), 93% of which were EBV positive. We performed an integrated molecular approach, including fluorescence in situ hybridization, targeted gene sequencing, and copy number (CN) arrays. Overall, PTLD-BL carried mutations in MYC, ID3, DDX3X, ARID1A, or CCND3 resembling IMC-BL, higher mutational burden than PTLD-DLBCL, and lesser CN alterations than IMC-BL. PTLD-DLBCL showed a very heterogeneous genomic profile with fewer mutations and CN alterations than IMC-DLBCL. Epigenetic modifiers and genes of the Notch pathway were the most recurrently mutated in PTLD-DLBCL (both 28%). Mutations in cell cycle and Notch pathways correlated with a worse outcome. All 7 patients with PTLD-BL were alive after treatment with pediatric B-cell non-Hodgkin lymphoma protocols, whereas 54% of patients with DLBCL were cured with immunosuppression reduction, rituximab, and/or low-dose chemotherapy. These findings highlight the low complexity of pediatric PTLD-DLBCL, their good response to low-intensity treatment, and the shared pathogenesis between PTLD-BL and EBV-positive IMC-BL. We also suggest new potential parameters that could help in the diagnosis and the design of better therapeutic strategies for these patients.

RAF1 gene fusions are recurrent driver events in infantile fibrosarcoma-like mesenchymal tumors.

Infantile fibrosarcomas (IFS) and congenital mesoblastic nephroma (CMN) are rare myofibroblastic tumors of infancy and early childhood commonly harboring the ETV6::NTRK3 gene fusion. IFS/CMN are considered as tumors with an 'intermediate prognosis' as they are locally aggressive, but rarely metastasize, and generally have a favorable outcome. A fraction of IFS/CMN-related neoplasms are negative for the ETV6::NTRK3 gene rearrangement and are characterized by other chimeric proteins promoting MAPK signaling upregulation. In a large proportion of these tumors, which are classified as IFS-like mesenchymal neoplasms, the contributing molecular events remain to be identified. Here, we report three distinct rearrangements involving RAF1 among eight ETV6::NTRK3 gene fusion-negative tumors with an original histological diagnosis of IFS/CMN. The three fusion proteins retain the entire catalytic domain of the kinase. Two chimeric products, GOLGA4::RAF1 and LRRFIP2::RAF1, had previously been reported as driver events in different cancers, whereas the third, CLIP1::RAF1, represents a novel fusion protein. We demonstrate that CLIP1::RAF1 acts as a bona fide oncoprotein promoting cell proliferation and migration through constitutive upregulation of MAPK signaling. We show that the CLIP1::RAF1 hyperactive behavior does not require RAS activation and is mediated by constitutive 14-3-3 protein-independent dimerization of the chimeric protein. As previously reported for the ETV6::NTRK3 fusion protein, CLIP1::RAF1 similarly upregulates PI3K-AKT signaling. Our findings document that RAF1 gene rearrangements represent a recurrent event in ETV6::NTRK3-negative IFS/CMN and provide a rationale for the use of inhibitors directed to suppress MAPK and PI3K-AKT signaling in these cancers. © 2024 The Pathological Society of Great Britain and Ireland.

Pediatric Plexiform Fibromyxoma: A Case Report.

The plexiform fibromyxoma is a rare mesenchymal tumor in adults that generally originates in the antrum of stomach, being its occurrence in pediatric patients exceptional. It was classified as a distinct entity by World Health Organization in 2010. No recurrences and metastases have been documented in many of the reported patients to date, being the surgical treatment curative. We report the case of a 3-month-old infant who presented to the emergency department with an episode of intestinal subocclusion requiring an emergent surgery. During the surgical intervention, a mass was identified in the jejunum, causing partial occlusion of its lumen. The surgical pathology report revealed an infiltrative tumor composed of spindle-shaped cells disposed in a stroma with a plexiform pattern alternating myxoid areas. These findings and the immunohistochemical characteristics of the neoplastic cells led to classify the tumor as a plexiform fibromyxoma. A description of the immunophenotype of this tumor is made and differential diagnosis with other gastrointestinal tumors is also discussed.

Decoding BCOR-ITD Sarcomas: Case Report of a Rare Pediatric Tumor With Challenges in Diagnosis.

Sarcomas characterized by BCOR gene alterations, are a distinct clinico-pathological group of high-grade tumors, that represent 5% of small round cell tumors without EWSR or FUS fusion. Diverse genetic alterations characterize this group, including BCOR-CCNB3 gene fusion being the most common alteration and less frequently internal tandem duplications (ITDs). We present a compelling case of a 3-year-old girl diagnosed with a high-grade nasoethmoidal sarcoma exhibiting BCOR-ITD. The diagnostic process illustrates the histological and immunophenotypic spectrum, requiring an extensive immunohistochemical panel and diverse molecular tests for accurate classification. Additionally, this case highlights the challenges in detecting BCOR-ITDs using different NGS panels, advocating for alternative molecular approaches. Our patient after 10 months since diagnosis is alive with progressive disease. This emphasizes the urgency for ongoing research to refine diagnostic methods and develop effective therapeutic strategies for these rare and aggressive tumors.

Distinct molecular profile of IRF4-rearranged large B-cell lymphoma.

Pediatric large B-cell lymphomas (LBCLs) share morphological and phenotypic features with adult types but have better prognosis. The higher frequency of some subtypes such as LBCL with IRF4 rearrangement (LBCL-IRF4) in children suggests that some age-related biological differences may exist. To characterize the genetic and molecular heterogeneity of these tumors, we studied 31 diffuse LBCLs (DLBCLs), not otherwise specified (NOS); 20 LBCL-IRF4 cases; and 12 cases of high-grade B-cell lymphoma (HGBCL), NOS in patients ≤25 years using an integrated approach, including targeted gene sequencing, copy-number arrays, and gene expression profiling. Each subgroup displayed different molecular profiles. LBCL-IRF4 had frequent mutations in IRF4 and NF-κB pathway genes (CARD11, CD79B, and MYD88), losses of 17p13 and gains of chromosome 7, 11q12.3-q25, whereas DLBCL, NOS was predominantly of germinal center B-cell (GCB) subtype and carried gene mutations similar to the adult counterpart (eg, SOCS1 and KMT2D), gains of 2p16/REL, and losses of 19p13/CD70. A subset of HGBCL, NOS displayed recurrent alterations of Burkitt lymphoma-related genes such as MYC, ID3, and DDX3X and homozygous deletions of 9p21/CDKN2A, whereas other cases were genetically closer to GCB DLBCL. Factors related to unfavorable outcome were age >18 years; activated B-cell (ABC) DLBCL profile, HGBCL, NOS, high genetic complexity, 1q21-q44 gains, 2p16/REL gains/amplifications, 19p13/CD70 homozygous deletions, and TP53 and MYC mutations. In conclusion, these findings further unravel the molecular heterogeneity of pediatric and young adult LBCL, improve the classification of this group of tumors, and provide new parameters for risk stratification.

Epstein-Barr virus-associated risk factors for post-transplant lymphoproliferative disease in pediatric liver transplant recipients.

BACKGROUND: Post-transplant lymphoproliferative disorder (PTLD) are the most common de novo malignancies after liver transplantation (LT) in children. The aim of our study was to assess the role of pre-LT EBV status and post-LT EBV viral load as risk factors for developing PTLD in a cohort of pediatric LT recipients. METHODS: Data of all children who underwent LT between January 2002 and December 2019 were collected. Two cohorts were built EBV pre-LT primary infected cohort and EBV post-LT primary infected cohort. Moreover, using the maximal EBV viral load, a ROC curve was constructed to find a cutoff point for the diagnosis of PTLD. RESULTS: Among the 251 patients included in the study, fifteen PTLD episodes in 14 LT recipients were detected (2 plasmacytic hyperplasia, 10 polymorphic PTLD, 2 monomorphic PTLD, and 1 Classical-Hodgkin's lymphoma). Patients of the EBV post-LT primary infected cohort were 17.1 times more likely to develop a PTLD than patients of the EBV pre-LT primary infected cohort (2.2-133.5). The EBV viral load value to predict PTLD was set at 211 000 UI/mL (93.3% sensitivity and 77.1% specificity; AUC 93.8%; IC 0.89-0.98). In EBV post-LT primary infected cohort, patients with a viral load above 211 000 were 30 times more likely to develop PTLD than patients with a viral load below this value (OR 29.8; 3.7-241.1; p < 0.001). CONCLUSIONS: The combination of pretransplant EBV serological status with EBV post-transplant viral load could be a powerful tool to stratify the risk of PTLD in pediatric LT patients.

Diffuse trophoblast damage is the hallmark of SARS-CoV-2-associated fetal demise.

Placental pathology in SARS-CoV-2-infected pregnancies seems rather unspecific. However, the identification of the placental lesions due to SARS-CoV-2 infection would be a significant advance in order to improve the management of these pregnancies and to identify the mechanisms involved in a possible vertical transmission. The pathological findings in placentas delivered from 198 SARS-CoV-2-positive pregnant women were investigated for the presence of lesions associated with placental SARS-CoV-2 infection. SARS-CoV-2 infection was investigated in placental tissues through immunohistochemistry, and positive cases were further confirmed by in situ hybridization. SARS-CoV-2 infection was also investigated by RT-PCR in 33 cases, including all the immunohistochemically positive cases. Nine cases were SARS-CoV-2-positive by immunohistochemistry, in situ hybridization, and RT-PCR. These placentas showed lesions characterized by villous trophoblast necrosis with intervillous space collapse and variable amounts of mixed intervillous inflammatory infiltrate and perivillous fibrinoid deposition. Such lesions ranged from focal to massively widespread in five cases, resulting in intrauterine fetal death. Two of the stillborn fetuses showed some evidence of SARS-CoV-2 positivity. The remaining 189 placentas did not show similar lesions. The strong association between trophoblastic damage and placenta SARS-CoV-2 infection suggests that this lesion is a specific marker of SARS-CoV-2 infection in placenta. Diffuse trophoblastic damage, massively affecting chorionic villous tissue, can result in fetal death associated with COVID-19 disease.

[Twin gestation with complete hydatidiform mole and a coexisting live fetus: A case report and review of the literature]. / Embarazo gemelar con mola hidatiforme completa y feto vivo asociado: reporte de un caso y revisión bibliográfica.

Twin pregnancies with complete hydatidiform mole and coexisting live fetus are very rare, with only about 300 reported cases. This type of pregnancy is considered a high obstetric risk due to the possibility of severe maternal-fetal complications. Although the clinical and ultrasound findings can be highly suggestive of this type of pregnancy, the definitive diagnosis is usually reached by histopathological examination. The differential diagnosis usually includes partial hydatidiform mole and hydropic pregnancies, which can present similar findings in specimens from the first trimester of pregnancy and thus it is important to interpret correctly the differentiating features. The use of immunohistochemistry for p57 can prove very useful, although some cases show an aberrant expression. We present a case of a twin pregnancy with complete hydatidiform mole associated with a live fetus, with magnetic resonance imaging and ultrasound for radiopathological correlation. We discuss the differential diagnosis and the utility of p57 immunohistochemistry.

MacroH2As regulate enhancer-promoter contacts affecting enhancer activity and sensitivity to inflammatory cytokines.

MacroH2A histone variants have a function in gene regulation that is poorly understood at the molecular level. We report that macroH2A1.2 and macroH2A2 modulate the transcriptional ground state of cancer cells and how they respond to inflammatory cytokines. Removal of macroH2A1.2 and macroH2A2 in hepatoblastoma cells affects the contact frequency of promoters and distal enhancers coinciding with changes in enhancer activity or preceding them in response to the cytokine tumor necrosis factor alpha. Although macroH2As regulate genes in both directions, they globally facilitate the nuclear factor κB (NF-κB)-mediated response. In contrast, macroH2As suppress the response to the pro-inflammatory cytokine interferon gamma. MacroH2A2 has a stronger contribution to gene repression than macroH2A1.2. Taken together, our results suggest that macroH2As have a role in regulating the response of cancer cells to inflammatory signals on the level of chromatin structure. This is likely relevant for the interaction of cancer cells with immune cells of their microenvironment.

Placental Tissue Destruction and Insufficiency From COVID-19 Causes Stillbirth and Neonatal Death From Hypoxic-Ischemic Injury.

CONTEXT.­: Perinatal death is an increasingly important problem as the coronavirus disease 2019 (COVID-19) pandemic continues, but the mechanism of death has been unclear. OBJECTIVE.­: To evaluate the role of the placenta in causing stillbirth and neonatal death following maternal infection with COVID-19 and confirmed placental positivity for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). DESIGN.­: Case-based retrospective clinicopathologic analysis by a multinational group of 44 perinatal specialists from 12 countries of placental and autopsy pathology findings from 64 stillborns and 4 neonatal deaths having placentas testing positive for SARS-CoV-2 following delivery to mothers with COVID-19. RESULTS.­: Of the 3 findings constituting SARS-CoV-2 placentitis, all 68 placentas had increased fibrin deposition and villous trophoblast necrosis and 66 had chronic histiocytic intervillositis. Sixty-three placentas had massive perivillous fibrin deposition. Severe destructive placental disease from SARS-CoV-2 placentitis averaged 77.7% tissue involvement. Other findings included multiple intervillous thrombi (37%; 25 of 68) and chronic villitis (32%; 22 of 68). The majority (19; 63%) of the 30 autopsies revealed no significant fetal abnormalities except for intrauterine hypoxia and asphyxia. Among all 68 cases, SARS-CoV-2 was detected from a body specimen in 16 of 28 cases tested, most frequently from nasopharyngeal swabs. Four autopsied stillborns had SARS-CoV-2 identified in internal organs. CONCLUSIONS.­: The pathology abnormalities composing SARS-CoV-2 placentitis cause widespread and severe placental destruction resulting in placental malperfusion and insufficiency. In these cases, intrauterine and perinatal death likely results directly from placental insufficiency and fetal hypoxic-ischemic injury. There was no evidence that SARS-CoV-2 involvement of the fetus had a role in causing these deaths.

Skip Segment Hirschsprung Disease Managed by Pull-Through of the Right Colon.

Hirschsprung disease is the most common neurocristopathy in children, resulting in the congenital loss of enteric ganglia. Rare reports of skip lesions have previously been reported in the literature. We present a case of skip lesions known prior to surgery and managed by pull-through of the right colon that allowed the preservation of the colon.

Implementation of a Gene Panel for Genetic Diagnosis of Primary Ciliary Dyskinesia. / Implementación de un panel de genes para el diagnóstico genético de la discinesia ciliar primaria.

INTRODUCTION: Primary ciliary dyskinesia (PCD) is characterized by an alteration in the ciliary structure causing difficulty in the clearance of respiratory secretions. Diagnosis is complex and based on a combination of techniques. The objective of this study was to design a gene panel including all known causative genes, and to corroborate their diagnostic utility in a cohort of Spanish patients. METHODS: This was a multicenter cross-sectional study of patients with a high suspicion of PCD, according to European Respiratory Society criteria, designed around a gene panel for massive sequencing using SeqCap EZ capture technology that included 44 genes associated with PCD. RESULTS: We included 79 patients, 53 of whom had a diagnosis of confirmed or highly probable PCD. The sensitivity of the gene panel was 81.1%, with a specificity of 100%. Candidate variants were found in some of the genes of the panel in 43 patients with PCD, 51.2% (22/43) of whom were homozygotes and 48.8% (21/43) compound heterozygotes. The most common causative genes were DNAH5 and CCDC39. We found 52 different variants, 36 of which were not previously described in the literature. CONCLUSIONS: The design and implementation of a tailored gene panel produces a high yield in the genetic diagnosis of PCD. This panel provides a better understanding of the causative factors involved in these patients and lays down the groundwork for future therapeutic approaches.

Immunofluorescence Analysis as a Diagnostic Tool in a Spanish Cohort of Patients with Suspected Primary Ciliary Dyskinesia.

Primary ciliary dyskinesia (PCD) is an autosomal recessive rare disease caused by an alteration of ciliary structure. Immunofluorescence, consisting in the detection of the presence and distribution of cilia proteins in human respiratory cells by fluorescence, has been recently proposed as a technique to improve understanding of disease-causing genes and diagnosis rate in PCD. The objective of this study is to determine the accuracy of a panel of four fluorescently labeled antibodies (DNAH5, DNALI1, GAS8 and RSPH4A or RSPH9) as a PCD diagnostic tool in the absence of transmission electron microscopy analysis. The panel was tested in nasal brushing samples of 74 patients with clinical suspicion of PCD. Sixty-eight (91.9%) patients were evaluable for all tested antibodies. Thirty-three cases (44.6%) presented an absence or mislocation of protein in the ciliary axoneme (15 absent and 3 proximal distribution of DNAH5 in the ciliary axoneme, 3 absent DNAH5 and DNALI1, 7 absent DNALI1 and cytoplasmatic localization of GAS8, 1 absent GAS8, 3 absent RSPH9 and 1 absent RSPH4A). Fifteen patients had confirmed or highly likely PCD but normal immunofluorescence results (68.8% sensitivity and 100% specificity). In conclusion, immunofluorescence analysis is a quick, available, low-cost and reliable diagnostic test for PCD, although it cannot be used as a standalone test.