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Malignant peripheral nerve sheath tumor (MPNST), an aggressive soft-tissue sarcoma, occurs in people with neurofibromatosis type 1 (NF1) and sporadically. Whole-genome and multiregional exome sequencing, transcriptomic, and methylation profiling of 95 tumor samples revealed the order of genomic events in tumor evolution. Following biallelic inactivation of NF1, loss of CDKN2A or TP53 with or without inactivation of polycomb repressive complex 2 (PRC2) leads to extensive somatic copy-number aberrations (SCNA). Distinct pathways of tumor evolution are associated with inactivation of PRC2 genes and H3K27 trimethylation (H3K27me3) status. Tumors with H3K27me3 loss evolve through extensive chromosomal losses followed by whole-genome doubling and chromosome 8 amplification, and show lower levels of immune cell infiltration. Retention of H3K27me3 leads to extensive genomic instability, but an immune cell-rich phenotype. Specific SCNAs detected in both tumor samples and cell-free DNA (cfDNA) act as a surrogate for H3K27me3 loss and immune infiltration, and predict prognosis., Significance: MPNST is the most common cause of death and morbidity for individuals with NF1, a relatively common tumor predisposition syndrome. Our results suggest that somatic copy-number and methylation profiling of tumor or cfDNA could serve as a biomarker for early diagnosis and to stratify patients into prognostic and treatment-related subgroups. This article is highlighted in the In This Issue feature, p. 517., (©2023 The Authors; Published by the American Association for Cancer Research.)

Background: Perivascular tumors, which include myopericytoma and myofibroma, are rare benign soft tissue neoplasms composed of perivascular smooth muscle cells. Most demonstrate characteristic morphology and are readily diagnosed. However, a recently identified hypercellular subset shows atypical histologic features and harbor unique SRF gene fusions. These cellular perivascular tumors can mimic other more common sarcomas with myogenic differentiation., Methods: Clinical, radiological, morphological, immunohistochemical, and molecular findings were reviewed., Results: A slow-growing, fluctuant mass was noted within the philtrum at 16 months. Ultrasonography revealed a well-circumscribed cystic hypoechoic lesion. A small (1.0 cm), tan, well-circumscribed soft-tissue mass was excised after continued growth. Histologically, the encapsulated tumor was hypercellular and composed of spindle cells with predominantly-storiform architecture, focal perivascular condensation, dilated branching thin-walled vessels, increased mitoses, and a smooth muscle immunophenotype. An SRF::NCOA2 fusion was identified., Conclusion: We report the first case of an SRF-rearranged cellular myopericytoma in the perioral region in a young child. This case expands the differential diagnosis of perioral soft tissue tumors with myogenic differentiation. We highlight key clinical, pathological, and molecular features. As we illustrate, these rare tumors pose a considerable diagnostic challenge, and risk misdiagnosis as sarcoma, most notably spindle cell rhabdomyosarcoma.

Purpose: Multiple FGFR inhibitors are currently in clinical trials enrolling adults with different solid tumors, while very few enroll pediatric patients. We determined the types and frequency of FGFR alterations ( FGFR1-4 ) in pediatric cancers to inform future clinical trial design., Methods: Tumors with FGFR alterations were identified from two large cohorts of pediatric solid tumors subjected to targeted DNA sequencing: The Dana-Farber/Boston Children's Profile Study (n = 888) and the multi-institution GAIN/iCAT2 (Genomic Assessment Improves Novel Therapy) Study (n = 571). Data from the combined patient population of 1,395 cases (64 patients were enrolled in both studies) were reviewed and cases in which an FGFR alteration was identified by OncoPanel sequencing were further assessed., Results: We identified 41 patients with tumors harboring an oncogenic FGFR alteration. Median age at diagnosis was 8 years (range, 6 months-26 years). Diagnoses included 11 rhabdomyosarcomas, nine low-grade gliomas, and 17 other tumor types. Alterations included gain-of-function sequence variants (n = 19), amplifications (n = 10), oncogenic fusions ( FGFR3 :: TACC3 [n = 3], FGFR1 :: TACC1 [n = 1], FGFR1 :: EBF2 [n = 1], FGFR1 :: CLIP2 [n = 1], and FGFR2 :: CTNNA3 [n = 1]), pathogenic-leaning variants of uncertain significance (n = 4), and amplification in combination with a pathogenic-leaning variant of uncertain significance (n = 1). Two novel FGFR1 fusions in two different patients were identified in this cohort, one of whom showed a response to an FGFR inhibitor., Conclusion: In summary, activating FGFR alterations were found in approximately 3% (41/1,395) of pediatric solid tumors, identifying a population of children with cancer who may be eligible and good candidates for trials evaluating FGFR-targeted therapy. Importantly, the genomic and clinical data from this study can help inform drug development in accordance with the Research to Accelerate Cures and Equity for Children Act.

To evaluate the clinical impact of molecular tumor profiling (MTP) with targeted sequencing panel tests, pediatric patients with extracranial solid tumors were enrolled in a prospective observational cohort study at 12 institutions. In the 345-patient analytical population, median age at diagnosis was 12 years (range 0-27.5); 298 patients (86%) had 1 or more alterations with potential for impact on care. Genomic alterations with diagnostic, prognostic or therapeutic significance were present in 61, 16 and 65% of patients, respectively. After return of the results, impact on care included 17 patients with a clarified diagnostic classification and 240 patients with an MTP result that could be used to select molecularly targeted therapy matched to identified alterations (MTT). Of the 29 patients who received MTT, 24% had an objective response or experienced durable clinical benefit; all but 1 of these patients received targeted therapy matched to a gene fusion. Of the diagnostic variants identified in 209 patients, 77% were gene fusions. MTP with targeted panel tests that includes fusion detection has a substantial clinical impact for young patients with solid tumors., (© 2022. The Author(s), under exclusive licence to Springer Nature America, Inc.)

Kaposiform lymphangiomatosis is an uncommon generalized lymphatic anomaly with distinctive clinical, radiologic, histopathologic, and molecular findings. Herein, we document the pathology in 43 patients evaluated by the Boston Children's Hospital Vascular Anomalies Center from 1999 to 2020. The most frequent presentations were respiratory difficulty, hemostatic abnormalities, and a soft tissue mass. Imaging commonly revealed involvement of some combination of mediastinal, pulmonary, pleural, and pericardial compartments and most often included spleen and skeleton. Histopathology was characterized by dilated, redundant, and abnormally configured lymphatic channels typically accompanied by dispersed clusters of variably canalized, and often hemosiderotic, spindled lymphatic endothelial cells that were immunopositive for D2-40, PROX1, and CD31. An activating lesional NRAS variant was documented in 9 of 10 patients. The clinical course was typically aggressive, marked by hemorrhage, thrombocytopenia, diminished fibrinogen levels, and a mortality rate of 21%., Competing Interests: Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Pediatric salivary gland fine-needle aspiration (FNA) is uncommon with a higher frequency of inflammatory lesions and a small proportion of malignancies. This international, multi-institutional cohort evaluated the application of the Milan System for Reporting Salivary Gland Cytopathology (MSRSGC) and the risk of malignancy (ROM) for each diagnostic category., Methods: Pediatric (0- to 21-year-old) salivary gland FNA specimens from 22 international institutions of 7 countries, including the United States, England, Italy, Greece, Finland, Brazil, and France, were retrospectively assigned to an MSRSGC diagnostic category as follows: nondiagnostic, nonneoplastic, atypia of undetermined significance (AUS), benign neoplasm, salivary gland neoplasm of uncertain malignant potential (SUMP), suspicious for malignancy (SM), or malignant. Cytology-histology correlation was performed where available, and the ROM was calculated for each MSRSGC diagnostic category., Results: The cohort of 477 aspirates was reclassified according to the MSRSGC as follows: nondiagnostic, 10.3%; nonneoplastic, 34.6%; AUS, 5.2%; benign neoplasm, 27.5%; SUMP, 7.5%; SM, 2.5%; and malignant, 12.4%. Histopathologic follow-up was available for 237 cases (49.7%). The ROMs were as follows: nondiagnostic, 5.9%; nonneoplastic, 9.1%; AUS, 35.7%; benign neoplasm, 3.3%; SUMP, 31.8%; SM, 100%; and malignant, 100%. Mucoepidermoid carcinoma was the most common malignancy (18 of 237; 7.6%), and it was followed by acinic cell carcinoma (16 of 237; 6.8%). Pleomorphic adenoma was the most common benign neoplasm (95 of 237; 40.1%)., Conclusions: The MSRSGC can be reliably applied to pediatric salivary gland FNA. The ROM of each MSRSGC category in pediatric salivary gland FNA is relatively similar to the ROM of each category in adult salivary gland FNA, although the reported rates for the different MSRSGC categories are variable across institutions., (© 2022 American Cancer Society.)

Kaposiform lymphangiomatosis (KLA) is a very rare form of generalized lymphatic anomaly, consisting of a diffuse proliferation of abnormal, dilated lymphatics, and small fascicles of hemosiderin-laden spindled lymphatic endothelial cells. KLA occurs in children and young adults and may present with multicentric disease, pleural and pericardial effusions, and life-threatening coagulopathy. Genetically, KLA most often harbors somatic activating mutations in NRAS. We recently encountered 3 cases of KLA with cellular features, resembling kaposiform hemangioendothelioma (KHE), and studied their clinicopathologic, radiologic, and molecular genetic features. The patients (1 male, 2 females; aged 2 years, 2 months, 4 years) presented with multicentric disease involving skin, soft tissue, bone, and spleen and thrombocytopenia/coagulopathy. Advanced imaging studies confirmed multicentric disease. Biopsies (skin, soft tissue, bone, and spleen) demonstrated both conventional KLA and much more cellular foci, consisting of sheets, nodules, glomeruloid structures, and sieve-like arrays of lymphatic endothelial cells (positive for CD31 and D2-40). Cellular areas superficially resembled KHE but displayed more epithelioid cytology and lacked surrounding hyaline fibrosis and minute platelet aggregates. Molecular genetic studies demonstrated NRAS c.181C > A p.Q61K (Gln61Lys) in 2 specimens from one patient and HRAS p.A59_Q61delinsGGSIL in another. Two patients were treated with sirolimus; all are currently alive with stable disease. We conclude that cellular morphology in KLA, a previously undescribed feature, does not appear to be associated with clinical features, site of disease, mutation type, response to sirolimus, or outcome. Although cellular KLA may mimic KHE, there are sufficient clinical, morphologic, and genetic differences such that these are likely unrelated diseases., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Aims: Recurrent alterations in receptor tyrosine kinase (RTK) and downstream effectors are described in infantile fibrosarcoma (IFS)/cellular congenital mesoblastic nephroma (cCMN) and a subset of spindle cell sarcomas, provisionally designated 'NTRK-rearranged' spindle cell neoplasms. These two groups of tumours demonstrate overlapping morphologies and harbour alterations in NTRK1/2/3, RET, MET, ABL1, ROS1, RAF1 and BRAF, although their relationship is not fully elucidated. We describe herein a cohort of paediatric tumours with clinicopathological features not typical for inflammatory myofibroblastic tumour, but rather with similarities to cCMN/IFS harbouring ALK fusions., Methods and Results: Clinicopathological features were assessed and partner agnostic targeted RNA sequencing on clinically validated platforms were performed. Tumours occurred in patients aged from 2 to 10 years (median age 2 years) with a 2:2 male to female ratio and an average size of 8.4 cm. Two tumours arose in soft tissues and two in the kidney. Morphological features included spindle to ovoid cells arranged in long fascicles or haphazardly within a myxoid to collagenised stroma; a subset of cases had either dilated, ectatic vessels or focal perivascular hyalinosis. By immunohistochemistry, all cases tested showed cytoplasmic expression of anaplastic lymphoma kinase (ALK) and one case demonstrated co-expression of CD34 and S100., Conclusions: This series of ALK-rearranged IFS-like tumours expands the spectrum of targetable kinases altered in these tumours and reinforces the potential overlap between IFS/cCMN-like tumours and the provisional entity of 'NTRK-rearranged' spindle cell neoplasms., (© 2021 John Wiley & Sons Ltd.)

Kinase alterations are increasingly recognised as oncogenic drivers in mesenchymal tumours. Infantile fibrosarcoma and the related renal tumour, congenital mesoblastic nephroma, were among the first solid tumours shown to harbour recurrent tyrosine kinase fusions, with the canonical ETV6::NTRK3 fusion identified more than 20 years ago. Although targeted testing has long been used in diagnosis, the advent of more robust sequencing techniques has driven the discovery of kinase alterations in an array of mesenchymal tumours. As our ability to identify these genetic alterations has improved, as has our recognition and understanding of the tumours that harbour these alterations. Specifically, this study will focus upon mesenchymal tumours harbouring NTRK or other kinase alterations, including tumours with an infantile fibrosarcoma-like appearance, spindle cell tumours resembling lipofibromatosis or peripheral nerve sheath tumours and those occurring in adults with a fibrosarcoma-like appearance. As publications describing the histology of these tumours increase so, too, do the variety kinase alterations reported, now including NTRK1/2/3, RET, MET, RAF1, BRAF, ALK, EGFR and ABL1 fusions or alterations. To date, these tumours appear locally aggressive and rarely metastatic, without a clear link between traditional features used in histological grading (e.g. mitotic activity, necrosis) and outcome. However, most of these tumours are amenable to new targeted therapies, making their recognition of both diagnostic and therapeutic import. The goal of this study is to review the clinicopathological features of tumours with NTRK and other tyrosine kinase alterations, discuss the most common differential diagnoses and provide recommendations for molecular confirmation with associated treatment implications., (© 2021 John Wiley & Sons Ltd.)

Bockenheimer disease is a venous malformation involving all tissues of an extremity. Patients have significant morbidity, and treatment is palliative. The purpose of this study was to identify the cause of Bockenheimer disease to develop pharmacotherapy for the condition. Paraffin-embedded tissue from nine individuals with Bockenheimer disease obtained during a clinically indicated operation underwent DNA extraction. Droplet digital polymerase chain reaction (ddPCR) was used to screen for variants most commonly associated with sporadic venous malformations ( TEK [NM_000459.5:c.2740C > T; p.Leu914Phe], PIK3CA [NM_006218.4:c.1624G > A; p.Glu542Lys and NM_006218.4:c.3140A > G; p.His1047Arg]). ddPCR detected a TEK L914F variant in all nine patients (variant allele fraction 2%-13%). PIK3CA E542K and H1047R variants were not identified in the specimens. Sanger sequencing and restriction enzyme digestion confirmed variants identified by ddPCR. A pathogenic variant in the endothelial cell tyrosine kinase receptor TEK is associated with Bockenheimer disease. Pharmacotherapy targeting the TEK signaling pathway might benefit patients with the condition., (© 2021 Sudduth et al.; Published by Cold Spring Harbor Laboratory Press.)

Inflammatory myofibroblastic tumor (IMT) is a rare, mesenchymal tumor that has an increased incidence in childhood. Tumors are usually isolated to the chest, abdomen, and retroperitoneum, but metastatic presentations can be seen. Presenting symptoms are nonspecific and include fever, weight loss, pain, shortness of breath, and cough. Approximately 85% of IMTs harbor actionable kinase fusions. The diagnosis can be delayed because of overlapping features with inflammatory disorders, such as elevated inflammatory markers, increased immunoglobin G levels, fever, weight loss, and morphologic similarity with nonmalignant conditions. We present a girl aged 11 years with a TFG-ROS1 fusion-positive tumor of the lung that was initially diagnosed as an immunoglobin G4-related inflammatory pseudotumor. She underwent complete left-sided pneumonectomy and later recurred with widely metastatic disease. We then report the case of a boy aged 9 years with widely metastatic TFG-ROS1 fusion-positive IMT with rapid molecular diagnosis. In both children, there was an excellent response to oral targeted therapy. These cases reveal that rapid molecular testing of inflammatory tumors is not only important for diagnosis but also reveals therapeutic opportunities. Targeted inhibitors produce significant radiologic responses, enabling potentially curative treatment approaches for metastatic ROS1 fusion IMT with previously limited treatment options. Primary care pediatricians and pediatric subspecialists have a crucial role in the early consultation of a pediatric oncology center experienced in molecular diagnostics to facilitate a comprehensive evaluation for children with inflammatory tumors., Competing Interests: POTENTIAL CONFLICT OF INTEREST: Dr DuBois has received consulting fees from Bayer and Loxo Oncology and travel expenses from Loxo Oncology, Roche, and Salarius Pharmaceuticals. Dr Church has received consulting fees from Bayer. Dr Janeway has received consulting fees from Bayer and Ipsen and speaking honoraria from Foundation Medicine and Takeda; the other authors have indicated they have no potential conflicts of interest to disclose., (Copyright © 2021 by the American Academy of Pediatrics.)

Background: Verrucous venous malformation (VVM), previously called "verrucous hemangioma," typically involves the dermis and the subcutaneous fat. We have encountered patients with VVM confined to the hypodermis., Materials and Methods: During a nearly 20-year period, 13 patients, aged 2-17 years, presented with a subcutaneous mass in the limb without clinically obvious epidermal alterations. Consequently, operative excisions did not include the skin., Results: Histopathologically, the specimens were composed of blood-filled channels with morphologic characteristics of capillaries and veins that infiltrated adipose tissue. Aggregates often formed nodules with variable fibrosis and a component of large and radially oriented vessels. A diagnosis of VVM was supported by endothelial immunopositivity for GLUT-1 (25%-75% immunopositive channels in 16/16 specimens); D2-40 (1%-25% channels in 14/15 specimens); and Prox-1 (1%-50% of channels in 14/16 specimens). A MAP3K3 mutation was identified by droplet digital PCR in 3 of the 6 specimens., Conclusions: Diagnosis of VVM in this uncommon location is challenging because of absence of epidermal changes and lack of dermal involvement. Imaging is not pathognomonic, and mimickers are many. Appropriate immunohistochemical stains and molecular analysis contribute to the correct diagnosis., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Undifferentiated embryonal sarcoma of the liver (UESL) is a rare aggressive neoplasm that occurs predominantly in children. Like mesenchymal hamartoma of the liver (MHL), UESL harbors recurrent rearrangements involving 19q13.3 and 19q13.4, a region of the genome that contains a primate-specific cluster of micro-RNAs. Here, we present a case of a high-grade neoplasm that arose in the left hepatic lobe of a 5-year-old male and gave rise to widespread lymph node, visceral, and soft tissue metastases. The tumor was composed of sheets, tubules, and papillae of epithelioid cells with rhabdoid morphology. INI1 and BRG1 expression were retained. Tumor cells diffusely expressed epithelial markers, including multiple keratins. While the morphologic and immunophenotypic features were suggestive of poorly differentiated carcinoma with rhabdoid features, the tumor was found to harbor the t(11;19)(q13;q13.3) translocation characteristic of UESL, as well as a TP53 mutation. Given the clinical presentation, imaging, clinical course, the tumor was classified as UESL with unusual, carcinoma-like histopathologic features. In the context of an unclassified high-grade hepatic tumor in a young child, molecular or cytogenetic testing for chromosome 19q13 alterations should be considered.

Alterations in the BCOR gene, including internal tandem duplications (ITDs) of exon 15 have emerged as important oncogenic changes that define several diagnostic entities. In pediatric cancers, BCOR ITDs have recurrently been described in clear cell sarcoma of kidney (CCSK), primitive myxoid mesenchymal tumor of infancy (PMMTI), and central nervous system high-grade neuroepithelial tumor with BCOR ITD in exon 15 (HGNET-BCOR ITDex15). In adults, BCOR ITDs are also reported in endometrial and other sarcomas. The utility of multiplex targeted RNA sequencing for the identification of BCOR ITD in pediatric cancers was investigated. All available archival cases of CCSK, PMMTI, and HGNET-BCOR ITDex15 were collected. Each case underwent anchored multiplex PCR library preparation with a custom-designed panel, with BCOR targeted for both fusions and ITDs. BCOR ITD was detected in all cases across three histologic subtypes using the RNA panel, with no other fusions identified in any of the cases. All BCOR ITDs occurred in the final exon, within 16 codons from the stop sequence. Multiplex targeted RNA sequencing from formalin-fixed, paraffin-embedded tissue is successful at identifying BCOR internal tandem duplications. This analysis supports the use of anchored multiplex PCR targeted RNA next-generation sequencing panels for identification of BCOR ITDs in pediatric tumors. The use of post-analytic algorithms to improve the detection of BCOR ITD using DNA panels was also explored., (Copyright © 2021 Association for Molecular Pathology and American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Infantile fibrosarcoma (IFS)/cellular congenital mesoblastic nephroma (cCMN) commonly harbors the classic ETV6-NTRK3 translocation. However, there are recent reports of mesenchymal tumors with IFS-like morphology harboring fusions of other receptor tyrosine kinases or downstream effectors, including NTRK1/2/3, MET, RET, and RAF1 fusions as well as one prior series with BRAF fusions. Discovery of these additional molecular drivers contributes to a more integrated diagnostic approach and presents important targets for therapy. Here we report the clinicopathologic and molecular features of 14 BRAF-altered tumors, of which 5 had BRAF point mutations and 10 harbored one or more BRAF fusions. Of the BRAF fusion-positive tumors, one harbored two BRAF fusions (FOXN3-BRAF, TRIP11-BRAF) and another harbored three unique alternative splice variants of EPB41L2-BRAF. Tumors occurred in ten males and four females, aged from birth to 32 years (median 6 months). Twelve were soft tissue based; two were visceral including one located in the kidney (cCMN). All neoplasms demonstrated ovoid to short spindle cells most frequently arranged haphazardly or in intersecting fascicles, often with collagenized stroma and a chronic inflammatory infiltrate. No specific immunophenotype was observed; expression of CD34, S100, and SMA was variable. To date, this is the largest cohort of BRAF-altered spindle cell neoplasms with IFS-like morphology, including not only seven novel BRAF fusion partners but also the first description of oncogenic BRAF point mutations in these tumors., (© 2021. The Author(s), under exclusive licence to United States & Canadian Academy of Pathology.)

Congenital tufting enteropathy (CTE) is a rare heritable cause of intractable diarrhea due to EPCAM mutation. Pathologic findings include intestinal villous atrophy, tufted discohesive tear-drop-shaped epithelium, and a normal brush border. In affected patients, absent intestinal epithelial cell adhesion molecule (EpCAM) expression results in loss of MOC31 immunostaining. CTE liver pathology has not yet been described. We identified CTE patients with liver biopsies and reviewed clinicopathologic material including MOC31 immunohistochemistry. Three CTE patients had 4 liver core biopsies (at ages 1, 5, 7, and 16 y), 2 for preintestinal transplant evaluation, and 2 (from a single patient) for pretreatment assessment of chronic hepatitis C; all had received parenteral nutrition (PN). All samples showed loss of biliary epithelial polarization and mild portal and lobular inflammation. Only the hepatitis C patient demonstrated fibrosis. One patient each had lobular neutrophilic microabscesses and macrovesicular steatosis. Proliferative ductular reactions were absent in CTE patients but present in all controls on PN for other reasons. MOC31 was absent in biliary epithelium and hepatocytes of all CTE patients; controls showed consistent strong membranous biliary epithelial and patchy membranous periportal hepatocyte staining. Our data show that, histologically, hepatopathy in CTE can be difficult to separate from comorbid disease including PN effect; however, the absent ductular reaction may be characteristic. MOC31 localization in the biliary epithelium and zone 1 hepatocytes of controls suggests these compartments of the liver might be most susceptible to effects of EpCAM deficiency. In addition, we validate the liver as suitable tissue for CTE diagnosis using MOC31 immunohistochemistry., Competing Interests: Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Objectives: The SWI/SNF complex core subunit SMARCB1 is inactivated in a variety of neoplasms that share characteristic "rhabdoid" cytomorphology. The aim of this study was to evaluate SMARCB1-deficient soft tissue neoplasms on cytology to identify diagnostic clues., Methods: Eleven SMARCB1-deficient tumors, including six epithelioid sarcomas, three malignant rhabdoid tumors, one epithelioid malignant peripheral nerve sheath tumor (MPNST), and one poorly differentiated chordoma with fine-needle aspiration (FNA), serous effusion, or touch prep (TP) from two institutions, were included. Targeted next-generation sequencing (NGS) was performed in two cases., Results: Evaluation of FNA (n = 4), effusion (n = 4), and TP (n = 3) in nine adult and two pediatric patients demonstrated cellular samples (n = 11), epithelioid cells with rhabdoid morphology (n = 9), eccentrically located nuclei with prominent nucleoli (n = 7), and cytoplasmic bodies (n = 4); two patients were diagnosed on FNA with cell block. Immunohistochemistry (IHC) demonstrated SMARCB1 loss in all cases and keratin and/or EMA expression in all but the epithelioid MPNST; NGS identified SMARCB1 inactivation in both cases., Conclusions: SMARCB1-deficient soft tissue neoplasms comprise a variety of tumors with epithelioid morphology and frequent expression of keratin and/or EMA. Recognition of characteristic rhabdoid morphology on cytology can prompt IHC and/or NGS testing for SMARCB1 deficiency and help establish the diagnosis., (© American Society for Clinical Pathology, 2021. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

WNT2B is a member of the Wnt family, a group of signal transduction proteins involved in embryologic development and stem cell renewal and maintenance. We recently reported homozygous nonsense variants in WNT2B in three individuals with severe, neonatal-onset diarrhea, and intestinal failure. Here we present a fourth case, from a separate family, with neonatal diarrhea associated with novel compound heterozygous WNT2B variants. One of the two variants was a frameshift variant (c.423del [p.Phe141fs]), while the other was a missense change (c.722 G > A [p.G241D]) that we predict through homology modeling to be deleterious, disrupting post-translational acylation. This patient presented as a neonate with severe diet-induced (osmotic) diarrhea and growth failure resulting in dependence on parenteral nutrition. Her gastrointestinal histology revealed abnormal cellular architecture particularly in the stomach and colon, including oxyntic atrophy, abnormal distribution of enteroendocrine cells, and a paucity of colonic crypt glands. In addition to her gastrointestinal findings, she had bilateral corneal clouding and atypical genital development later identified as a testicular 46,XX difference/disorder of sexual development. Upon review of the previously reported cases, two others also had anterior segment ocular anomalies though none had atypical genital development. This growing case series suggests that variants in WNT2B are associated with an oculo-intestinal (and possibly gonadal) syndrome, due to the protein's putative involvement in multiple developmental and stem cell maintenance pathways.

Vascular anomalies, further classified into vascular tumors and malformations, often involve the head and neck region of children. These entities may raise diagnostic dilemmas, as they often demonstrate heterogenous and overlapping histologic features. The aim of this paper is to provide an overview of the common vascular anomalies in the head and neck region of children. Specific entities discussed include infantile hemangioma, congenital hemangioma, tufted angioma, kaposiform hemangioendothelioma, and various vascular malformations. Clinicopathologic features and associated molecular associations are reviewed.

Vascular anomalies are composed of tumors and malformations and with overlapping histologies, thus are often misdiagnosed or labeled with imprecise terminology. Lesions are common and usually diagnosed during infancy or childhood; the estimated prevalence is 4.5%. Vascular tumors rapidly enlarge postnatally and demonstrate endothelial proliferation. Malformations are errors in vascular development with stable endothelial turnover; they are typically named based on the primary vessel that is malformed (capillary, arterial, venous, lymphatic). This article reviews the pathologic and molecular genetic characteristics for select recently described vascular anomalies., Competing Interests: Disclosure The authors declare that they have nothing to disclose., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objective: To describe the clinical, radiologic, and histopathologic features of "congenital disseminated pyogenic granuloma" involving various organs with high morbidity related to cerebral hemorrhagic involvement., Study Design: We searched the database of the Vascular Anomalies Center at Boston Children's Hospital from 1999 to 2019 for patients diagnosed as having multiple vascular lesions, visceral vascular tumors, congenital hemangiomatosis, multiple pyogenic granulomas, or multiple vascular lesions without a definite diagnosis. A retrospective review of the medical records, photographs, histopathologic, and imaging studies was performed. Only patients with imaging studies and histopathologic diagnosis of pyogenic granuloma were included., Results: Eight children (5 male, 3 female) had congenital multifocal cutaneous vascular tumors. Lesions also were found in the brain (n = 7), liver (n = 4), spleen (n = 3), muscles (n = 4), bone (n = 3), retroperitoneum (n = 3), and intestine/mesentery (n = 2). Less commonly affected were the spinal cord, lungs, kidneys, pancreas, and adrenal gland (n = 1 each). The mean follow-up period was 21.8 months. The cerebral and visceral lesions were hemorrhagic with severe neurologic sequelae. The histopathologic diagnosis was pyogenic granuloma with prominent areas of hemorrhage and necrosis. The endothelial cells had enlarged nuclei, pale cytoplasm and were immunopositive for CD31 and negative for D2-40 and glucose transporter 1., Conclusions: Congenital disseminated pyogenic granuloma is a distinct multisystemic aggressive disorder that primarily affects the skin, brain, visceral organs, and musculoskeletal system. Differentiation of this entity from other multiple cutaneous vascular lesions is critical because of possible cerebral hemorrhagic involvement., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Introduction: Tissue from pediatric solid tumors is in high demand for use in high-impact research studies, making the allocation of tissue from an anatomic pathology laboratory challenging. We designed, implemented, and assessed an interdepartmental process to optimize tissue allocation of pediatric solid tumors for both clinical care and research., Methods: Oncologists, pathologists, surgeons, interventional radiologists, pathology technical staff, and clinical research coordinators participated in the workflow design. Procedures were created to address patient identification and consent, prioritization of protocols, electronic communication of requests, tissue preparation, and distribution. Pathologists were surveyed about the value of the new workflow., Results: Over a 5-year period, 644 pediatric solid tumor patients consented to one or more studies requesting archival or fresh tissue. Patients had a variety of tumor types, with many rare and singular diagnoses. Sixty-seven percent of 1768 research requests were fulfilled. Requests for archival tissue were fulfilled at a significantly higher rate than those for fresh tissue (P > .001), and requests from resection specimens were fulfilled at a significantly higher rate than those from biopsies (P > .0001). In an anonymous survey, seven of seven pathologists reported that the process had improved since the introduction of the electronic communication model., Conclusions: A collaborative and informed model for tissue allocation is successful in distributing archival and fresh tissue for clinical research studies. Our workflows and policies have gained pathologists' approval and streamlined our processes. As clinical and research programs evolve, a thoughtful tissue allocation process will facilitate ongoing research., (© 2020 Wiley Periodicals, Inc.)

Purpose: Several aggressive pediatric cancers harbor alterations in SMARCB1 , including rhabdoid tumors, epithelioid sarcoma, and chordoma. As tumor profiling has become more routine in clinical care, we investigated the relationship between SMARCB1 genetic variants identified by next-generation sequencing (NGS) and INI1 protein expression. Therapeutic approaches for INI1-deficient tumors are limited. Early reports suggest a potential role for immune checkpoint inhibition in these patients. Thus, we also investigated PD-L1 and CD8 expression in INI1-negative pediatric brain and solid tumors., Experimental Design: We performed immunohistochemistry (IHC) for INI1 and immune markers (PD-L1, CD8, and CD163) and NGS on tumor samples from 43 pediatric patients who had tumors with INI1 loss on previous IHC or SMARCB1 genomic alterations on prior somatic sequencing., Results: SMARCB1 two-copy deletions and inactivating mutations on NGS were associated with loss of INI1 protein expression. Single-copy deletion of SMARCB1 was not predictive of INI1 loss in tumor histologies not known to be INI1-deficient. In the 27 cases with INI1 loss and successful tumor sequencing, 24 (89%) had a SMARCB1 alteration detected. In addition, 47% (14/30) of the patients with INI1-negative tumors had a tumor specimen that was PD-L1 positive and 60% (18/30) had positive or rare CD8 staining. We report on 3 patients with INI1-negative tumors with evidence of disease control on immune checkpoint inhibitors., Conclusions: A significant proportion of the INI1-negative tumors express PD-L1, and PD-L1 positivity was associated with extracranial tumor site. These results suggest that clinical trials of immune checkpoint inhibitors are warranted in INI1-negative pediatric cancers., (©2020 American Association for Cancer Research.)

Cranial fasciitis is a benign myofibroproliferative lesion of the scalp and underlying bones typically occurring in the pediatric population. Histologically, it is characterized by loose fascicles of stellate cells in a fibromyxoid background, findings similar to those described in the closely related variant nodular fasciitis. Previously characterized as a reactive process, the identification of USP6 translocations in over 90% of nodular fasciitis cases prompted their reclassification as a clonal neoplastic process. Unlike nodular fasciitis, the molecular underpinnings of cranial fasciitis are less clear. While a subset of cranial fasciitis has been associated with Wnt/β-catenin pathway dysregulation, recent case reports suggest that this entity may also harbor USP6 fusions, a finding we sought to further investigate. We identified fifteen archival cases of cranial fasciitis, five females and ten males ranging in age from 3 months to 9 years (median 11 months), composed of formalin-fixed paraffin-embedded and fresh frozen tissues (11 and 4 cases respectively). Samples were evaluated on an RNA-based targeted sequencing panel targeting genes recurrently rearranged in neoplasia, including USP6. Five of fifteen cases (33%) were positive for USP6 rearrangements predicted to result in the fusion of the entire USP6 coding region to the promoter of the 5' partner, (three of which were novel):  two SERPINH1-USP6 (novel) and one each of COL3A1-USP6 (novel), SPARC-USP6, and MYH9-USP6. These results demonstrate the recurrent nature of USP6 rearrangements in cranial fasciitis, and highlight the success of targeted RNA sequencing in identifying known and novel fusion partners. The identification of USP6 promoter-swapping rearrangements is helpful in understanding the underlying biology of cranial fasciitis, and reinforces its biologic relationship to nodular fasciitis. Targeted RNA sequencing is a helpful tool in diagnosing this pseudosarcomatous lesion.

Extracranial arteriovenous malformation (AVM) is most commonly caused by MAP2K1 mutations in the endothelial cell. The purpose of this study was to determine if local tissue overgrowth associated with AVM is caused by direct or indirect effects of the MAP2K1 mutation (i.e., cell-autonomous or cell-non autonomous). Because cartilage does not have blood vessels, we studied ear AVMs to determine if overgrown cartilage contained AVM-causing mutations. Cartilage was separated from its surrounding tissue and isolated by laser capture microdissection. Droplet digital PCR (ddPCR) was used to identify MAP2K1 mutations. MAP2K1 (p.K57N) variants were present in the tissue adjacent to the cartilage [mutant allele frequency (MAF) 6-8%], and were enriched in endothelial cells (MAF 51%) compared to non-endothelial cells (MAF 0%). MAP2K1 mutations were not identified in the overgrown cartilage, and thus local cartilage overgrowth likely results from the effects of adjacent mutant blood vessels (i.e., cell-non autonomous).

Background: Fibroadipose vascular anomaly (FAVA) is a recently-defined vascular malformation often involving the extremities and presenting in childhood. Patients may present to orthopaedic surgeons with pain, swelling, joint contractures, and leg length discrepancy. There is no established therapy or treatment paradigm. We report on outcomes following surgical excision for patients with this condition., Methods: Between 2007 and 2016, all 35 patients that underwent excision of lower-extremity FAVA were retrospectively reviewed using a combination of medical records, radiologic findings, and telemedicine reviews., Results: Mean age at initial presentation was 12.3±6.8 years. Mean follow-up from time of definitive diagnosis at our institution was 66 months (range: 12 to 161 mo). Mean follow-up after surgery was 35 months (range: 6 to 138 mo). Females were affected more than males (71% vs. 29%). The most common location of FAVA was in the calf (49%), followed by the thigh (40%). The most commonly involved muscle was gastrocnemius (29%), followed by the quadriceps (26%). At latest follow-up after surgery, there was an improvement in the proportion of patients with pain at rest (63% vs. 29%), pain with activity (100% vs. 60%), as well as analgesia use (94% vs. 37%). Fourteen patients (40%) had symptomatic residual disease or recurrence of FAVA requiring further treatment. Six patients (17%) required further surgery and 6 (17%) required further interventional radiologic procedures. Three patients (9%) required eventual amputation for intractable pain and loss of function. Lesions with direct nerve involvement were associated with persistent neuropathic symptoms at latest follow-up (P=0.002) as well as symptomatic residual disease and/or recurrence requiring further treatment (P=0.01). Seventeen patients (49%) had 19 preoperative joint contractures. Eighteen of the 19 contractures (95%) had sustained improvement at latest follow-up., Conclusions: In carefully selected patients, surgical excision of FAVA results in improvement of symptoms. However, symptomatic residual disease and/or recurrence are not uncommon. Direct nerve involvement is associated with a worse outcome., Level of Evidence: Level IV-case series.

Background: The term "intramuscular hemangioma capillary type" (IHCT) refers to a fast-flow vascular lesion that is classified as a tumor, although its phenotype overlaps with arteriovenous malformation (AVM). The purpose of this study was to identify somatic mutations in IHCT., Methods: Affected tissue specimens were obtained during a clinically indicated procedure. The diagnosis of IHCT was based on history, physical examination, imaging and histopathology. Because somatic mutations in cancer-associated genes can cause vascular malformations, we sequenced exons from 446 cancer-related genes in DNA from 7 IHCT specimens. We then performed mutation-specific droplet digital PCR (ddPCR) to independently test for the presence of a somatic mutation found by sequencing and to screen one additional IHCT sample., Results: We detected somatic mutations in 6 of 8 IHCT specimens. Four specimens had a mutation in MAP2K1 (p.Q58_E62del, p.P105_I107delinsL, p.Q56P) and 2 specimens had mutations in KRAS (p.K5E and p.G12D, p.G12D and p.Q22R). Mutant allele frequencies detected by sequencing and confirmed by ddPCR ranged from 2 to 15%., Conclusions: IHCT lesions are phenotypically similar to AVMs and contain the same somatic MAP2K1 or KRAS mutations, suggesting that IHCT is on the AVM spectrum. We propose calling this lesion "intramuscular fast-flow vascular anomaly."

Purpose: Kaposiform lymphangiomatosis (KLA) is a rare, frequently aggressive, systemic disorder of the lymphatic vasculature, occurring primarily in children. Even with multimodal treatments, KLA has a poor prognosis and high mortality rate secondary to coagulopathy, effusions, and systemic involvement. We hypothesized that, as has recently been found for other vascular anomalies, KLA may be caused by somatic mosaic variants affecting vascular development., Methods: We performed exome sequencing of tumor samples from five individuals with KLA, along with samples from uninvolved control tissue in three of the five. We used digital polymerase chain reaction (dPCR) to validate the exome findings and to screen KLA samples from six other individuals., Results: We identified a somatic activating NRAS variant (c.182 A>G, p.Q61R) in lesional tissue from 10/11 individuals, at levels ranging from 1% to 28%, that was absent from the tested control tissues., Conclusion: The activating NRAS p.Q61R variant is a known "hotspot" variant, frequently identified in several types of human cancer, especially melanoma. KLA, therefore, joins a growing group of vascular malformations and tumors caused by somatic activating variants in the RAS/PI3K/mTOR signaling pathways. This discovery will expand treatment options for these high-risk patients as there is potential for use of targeted RAS pathway inhibitors.

Pediatric mesenchymal tumors harboring variant NTRK fusions (ETV6-negative) are being increasingly described; however, the histologic and clinical features of these variant NTRK tumors and their relationship to classic infantile fibrosarcoma are not well characterized. A better understanding of the clinicopathologic features of these tumors is necessary, and would aid in both early diagnosis and treatment. Therefore, the aim of this study was to characterize a series of pediatric NTRK-rearranged mesenchymal tumors, including classic ETV6-NTRK3 fused tumors and tumors with variant (non-ETV6) NTRK fusions. The clinical features, morphology, immunophenotype, and genetics of 12 classic ETV6-NTRK3 fused infantile fibrosarcoma and 18 variant NTRK-rearranged mesenchymal tumors were evaluated. For both classic and variant groups, the age at diagnosis ranged from birth to 15 years (median, 4 mo) with no sex predilection; the most common sites involved were the extremities and trunk. The rate of local recurrence and metastasis were not significantly different (recurrence rate: 11% classic, 40% variant; metastatic rate: 18% classic, 25% variant). Classic and variant NTRK tumors had an overlapping spectrum of histologic features, containing haphazardly arranged primitive cells in a myxoid background and/or spindle cells in long fascicles. Both groups showed diffuse pan-TRK expression by immunohistochemistry. Otherwise, the immunoprofile was nonspecific, but similar between both groups. No statistical difference was seen in any clinicopathologic feature between the classic ETV6-NTRK3 and variant fusion cohorts. Pediatric NTRK-rearranged mesenchymal tumors with both classic and variant fusions likely represent a spectrum of disease with shared, recognizable cliniopathologic features.

Adipocytic neoplasms in the pediatric population demonstrate a different histologic spectrum and frequency than in adults. The vast majority of these tumors are benign, with lipoma being the most common entity. The identification of signature cytogenetic and molecular alterations for certain lesions, such as PLAG1 gene rearrangement in lipoblastoma and FUS-DDIT3 fusion in myxoid liposarcoma, has been helpful in approaching these neoplasms and aiding in confirming the diagnosis. Furthermore, it is important for pathologists to recognize that adipocytic neoplasms may be associated with different syndromes with potential impact in managing such patients. This review provides a summary of the clinical pictures, histologic characteristics, molecular alterations, differential diagnoses, and syndromic associations of the commonly encountered fatty tumors in children., (Published by Elsevier Inc.)

Lipofibromatosis is a rare pediatric soft tissue tumor with predilection for the hands and feet. Previously considered to represent "infantile fibromatosis", lipofibromatosis has distinctive morphological features, with mature adipose tissue, short fascicles of bland fibroblastic cells, and lipoblast-like cells. Very little is known about the genetic underpinnings of lipofibromatosis. Prompted by our finding of the FN1-EGF gene fusion, previously shown to be a characteristic feature of calcifying aponeurotic fibroma (CAF), in a morphologically typical case of lipofibromatosis that recurred showing features of CAF, we studied a cohort of 20 cases of lipofibromatosis for this and other genetic events. The cohort was composed of 14 males and 6 females (median age 3 years; range 1 month-14 years). All primary tumors showed classical lipofibromatosis morphology. Follow-up disclosed three local recurrences, two of which contained calcifying aponeurotic fibroma-like nodular calcifications in addition to areas of classic lipofibromatosis, and no metastases. By FISH and RNA sequencing, four cases were positive for FN1-EGF and one case each showed an EGR1-GRIA1, TPR-ROS1, SPARC-PDGFRB, FN1-TGFA, EGFR-BRAF, VCL-RET, or HBEGF-RBM27 fusion. FN1-EGF was the only recurrent fusion, suggesting that some cases of "lipofibromatosis" may represent calcifying aponeurotic fibroma lacking hallmark calcifications. Several of the genes involved in fusions (BRAF, EGFR, PDGFRB, RET, and ROS1) encode receptor tyrosine kinases (RTK), or ligands to the RTK EGFR (EGF, HBEGF, TGFA), suggesting a shared deregulation of the PI3K-AKT-mTOR pathway in a large subset of lipofibromatosis cases.

We present our experience with ten well-characterized malignant tenosynovial giant cell tumors, including detailed immunohistochemical analysis of all cases and molecular cytogenetic study for CSF1 rearrangement in a subset. Cases occurred in 7 M and 3 F (mean age: 52 years; range: 26-72 years), and involved the ankle/foot (n = 1), finger/toe (n = 3), wrist (n = 1), pelvic region (n = 3), leg (n = 1), and thigh (n = 1). There were eight primary and two secondary malignant tenosynovial giant cell tumors. Histologically, all cases showed definite areas of typical tenosynovial giant cell tumor. The malignant areas varied in appearance. In some cases, isolated malignant-appearing large mononuclear cells with high nuclear grade and mitotic activity were identified within otherwise-typical tenosynovial giant cell tumor, as well as forming larger masses of similar-appearing malignant cells. Occasionally, these nodules of malignant large mononuclear cells showed transition to pleomorphic spindle cell sarcoma, with varying degrees of collagenization and myxoid change. One malignant tenosynovial giant cell tumor was composed of sheets of monotonous large mononuclear cells with high nuclear grade, growing in a hyalinized, osteoid-like matrix, with areas of heterologous osteocartilaginous differentiation. Mitotic activity ranged from 2 to 34 mitoses per 10 HPF (mean 18/10 HPF). Geographic necrosis was observed in four cases. The malignant-appearing large mononuclear cells were consistently positive for clusterin and negative for CD163, CD68, and CD11c. Desmin was positive in a small minority of these cells. Areas in malignant tenosynovial giant cell tumor resembling pleomorphic spindle cell sarcoma or osteo/chondrosarcoma showed loss of clusterin expression. RANKL immunohistochemistry was positive in the large mononuclear cells in eight cases. Two cases showed an unbalanced rearrangement of the CSF1 locus. Follow-up (nine patients; range 0.5-66 months; mean 20 months) showed three patients dead of disease, with three other living patients having lung and lymph node metastases; three patients were disease-free. We conclude that malignant tenosynovial giant cell tumors are highly aggressive sarcomas with significant potential for locally destructive growth, distant metastases, and death from disease. The morphologic and immunohistochemical features of these tumors and the presence of CSF1 rearrangements support origin of malignant tenosynovial giant cell tumor from synoviocytes.

Fetuses with hypoplastic left heart syndrome (HLHS) and intact atrial septum are a particular subset of HLHS neonates with high perinatal mortality. The reported mortality in these patients is 50% to 70%, even with prenatal diagnosis. Prenatal left atrial and pulmonary venous hypertension results in abnormal pulmonary vascular and parenchymal development. The goal of this study was to compare the sonographic appearance of the lungs in fetuses with HLHS/intact atrial septum to neonatal outcome and/or pathology in cases where in utero intervention was performed to open the atrial septum. We found that lung inhomogeneity on ultrasound corresponded to peripheral lymphatic dilatation at autopsy and was associated with a dismal prognosis even when in utero intervention was successful.

Bizarre Parosteal Osteochondromatous Proliferation (BPOP) is a benign tumor-like lesion that has recently been reported to have an association with a specific translocation t(1:17)(q32;q21)[1]. Like other reactive periosteal lesions, BPOP can be diagnostically challenging, with the ever-present possibility of a potentially devastating erroneous diagnosis of malignancy. These lesions are often clinically, radiologically and histopathologically ambiguous, with rapid but circumscribed, non-infiltrative growth patterns, and histological atypia, but without overt features of malignancy. However, recent published reports have better characterized radiological [2] as well as histological features that aid in making an accurate diagnosis. In spite of all these advances, one of the biggest challenges in making the correct diagnosis still remains the inexperience of the practicing pathologist with this lesion, simply due to its rarity. We present a case of Nora's lesion in the distal ulna of an 8 year-old girl, in which, besides the histological features, we were able to demonstrate the translocation t(1:17)(q32;q21). Thus, we would like to emphasize the utility of cytogenetic studies in the correct and rapid diagnosis of clinically and radiologically ambiguous periosteal-based lesion.