Pediatric Fibromatosis Lacks the Internal Tandem Duplication of EGFR Seen in Congenital Mesoblastic Nephroma.

Classical and mixed congenital mesoblastic nephroma (CMN) are characterized by an internal tandem duplication (ITD) of the EGFR gene, in contrast to cellular CMN that usually harbors an ETV6::NTRK3 gene fusion. This same fusion occurs in infantile fibrosarcoma, and this tumor can be considered as the soft tissue equivalent of cellular CMN. A soft tissue equivalent of classic/mixed CMN remains undefined at the genetic level. Since classical CMN resembles fibromatosis of soft tissue histologically, we asked whether fibromatosis in children might show EGFR ITD. ITD was investigated using the polymerase chain reaction and primers for exons 18 and 25 of the EGFR gene. Seven of the eight cases of classical or mixed CMN were positive by this approach, but none of the five cellular CMNs. Of 11 cases of fibromatosis (six plantar, two digital, and three desmoid), none were positive for EGFR ITD. Within the limits of this small study, we conclude that pediatric fibromatosis is likely not characterized by EGFR ITD. There are isolated reports of pediatric soft tissue tumors that harbor EGFR ITD, but these have the appearance of infantile fibrosarcoma or mixed CMN rather than fibromatosis. We did not find any such cases, since all 14 cases of infantile fibrosarcoma in our study had an ETV6::NTRK3 fusion. The soft tissue tumors with EGFR ITD are not a morphologic match for the low-grade histology of classical CMN. Whether they have a similar favorable biology or behave more like fibrosarcoma with an ETV6::NTRK3 fusion or an alternative fusion involving other kinases remains to be determined.

Canadian Multicentric Pan-TRK (CANTRK) Immunohistochemistry Harmonization Study.

Tumor-agnostic testing for NTRK1-3 gene rearrangements is required to identify patients who may benefit from TRK inhibitor therapies. The overarching objective of this study was to establish a high-quality pan-TRK immunohistochemistry (IHC) screening assay among 18 large regional pathology laboratories across Canada using pan-TRK monoclonal antibody clone EPR17341 in a ring study design. TRK-fusion positive and negative tumor samples were collected from participating sites, with fusion status confirmed by panel next-generation sequencing assays. Each laboratory received: (1) unstained sections from 30 cases of TRK-fusion-positive or -negative tumors, (2) 2 types of reference standards: TRK calibrator slides and IHC critical assay performance controls (iCAPCs), (3) EPR17341 antibody, and (4) suggestions for developing IHC protocols. Participants were asked to optimize the IHC protocol for their instruments and detection systems by using iCAPCs, to stain the 30 study cases, and to report the percentage scores for membranous, cytoplasmic, and nuclear staining. TRK calibrators were used to assess the analytical sensitivity of IHC protocols developed by using the 2 reference standards. Fifteen of 18 laboratories achieved diagnostic sensitivity of 100% against next-generation sequencing. The diagnostic specificity ranged from 40% to 90%. The results did not differ significantly between positive scores based on the presence of any type of staining vs the presence of overall staining in ≥1% of cells. The median limit of detection measured by TRK calibrators was 76,000 molecules/cell (range 38,000 to >200,000 molecules/cell). Three different patterns of staining were observed in 19 TRK-positive cases, cytoplasmic-only in 7 samples, nuclear and cytoplasmic in 9 samples, and cytoplasmic and membranous in 3 samples. The Canadian multicentric pan-TRK study illustrates a successful strategy to accelerate the multicenter harmonization and implementation of pan-TRK immunohistochemical screening that achieves high diagnostic sensitivity by using laboratory-developed tests where laboratories used centrally developed reference materials. The measurement of analytical sensitivity by using TRK calibrators provided additional insights into IHC protocol performance.

Imaging features of pediatric angiosarcomas: clinical, pathologic, and radiological review.

BACKGROUND: Angiosarcomas are rare malignant vascular tumors and there is scarcity of data on their imaging features. OBJECTIVE: To review and illustrate the imaging, clinical, and pathologic features of angiosarcoma in children. MATERIALS AND METHODS: A list of pathologically proven angiosarcoma seen between Nov 1992 and Jan 2023 was obtained from a pathology database and picture archiving and communication system. Those with pre-treatment imaging available on our PACS were included in the study. Imaging studies were reviewed by two readers in consensus. RESULTS: A total of six children (two males and four females; median age of 8.8 years; range 2.9 years to 15.5 years) had angiosarcoma during the study period. Organ of origin included breast (n = 2), liver (n = 2), spleen (n = 1), and paranasal sinuses (n = 1). The patient with splenic angiosarcoma had Li-Fraumeni syndrome. Five patients had a single lesion while one had multifocal lesions. The tumors were large with a median diameter of 12.9 cm (range 2.7 cm to 24 cm). Most tumors were heterogeneous on T2-weighted imaging with hemorrhage and necrosis and showed heterogeneous enhancement. Three had well-defined borders and three had infiltrative borders. None of the tumors showed calcifications. Two tumors in the liver showed gradual non-centripetal progressive diffuse enhancement on dynamic imaging. One patient had metastases at presentation and four patients subsequently developed metastases on follow-up. Five patients underwent surgical resection and chemotherapy; one patient with a liver lesion underwent arterial embolization followed by liver transplant. Three patients died at the last follow-up. CONCLUSION: The imaging features of angiosarcomas are nonspecific, but the tumors are large heterogeneously enhancing masses with hemorrhage and necrosis. Hepatic angiosarcomas may show non-centripetal progressive and heterogeneous enhancement on dynamic imaging.

Utilizing therapeutic drug monitoring to optimize therapy with eculizumab and mycophenolate mofetil in a child with C3 glomerulonephritis.

BACKGROUND: C3 glomerulonephritis (C3GN) can be a devastating disease with poor response to immunosuppressive therapy. Complement inhibition with eculizumab has had equivocal results in patients with C3GN. CASE-DIAGNOSIS/TREATMENT: We report a case of a 6-year-old boy with C3GN presenting with nephrotic syndrome, severe hypertension and impaired kidney function. He did not respond to initial treatment with prednisone and mycophenolate (mofetil and sodium), and subsequent treatment with standard dosing of eculizumab. Pharmacokinetic studies identified a lack of eculizumab exposure and subsequent intensification of treatment with weekly dosing of eculizumab led to significant clinical improvement: his kidney function normalized, hypertension (weaned off 3 antihypertensive drugs), edema and proteinuria improved. Additionally, exposure to mycophenolic acid (MPA), active metabolite of mycophenolate, determined by area under the concentration-time curve of MPA was low throughout, despite significant dosing escalation. CONCLUSIONS: This case report demonstrates that individualized therapy guided by therapeutic drug monitoring might be needed in patients with nephrotic range proteinuria treated with eculizumab and mycophenolate (mofetil and sodium), an important finding that needs to be considered for further treatment trials.

Hepatic ultrastructural features distinguish paediatric Wilson disease from NAFLD and autoimmune hepatitis.

BACKGROUND AND AIMS: Wilson disease (WD) has diverse presentations that frequently mimic other liver diseases. Distinguishing WD from non-alcoholic fatty liver disease (NAFLD) and autoimmune hepatitis (AIH), can be difficult and has critical implications for medical management. This study aimed to examine the utility of histological features of WD in children compared to those with NAFLD and AIH. METHODS: A review of liver biopsy slides was performed in children with a clinical and/or genetic diagnosis of WD, seen at the Hospital for Sick Children between 1981 and 2019 and compared to controls with NAFLD and AIH. 37 children with WD and 37 disease controls (20 NAFLD; 17 AIH) were included. Three pathologists, blind to clinical details and diagnosis, reviewed all liver biopsies to reach consensus. Clinical and histopathologic features were compared between groups. RESULTS: Most WD cases displayed steatosis or steatohepatitis on histology (34/37), active AIH-pattern in 1 and inactive cirrhosis in 2 cases. Electron microscopy (EM) findings of mitochondrial abnormalities including dilated tips of cristae, pleomorphism, membrane duplication and dense matrix were more frequent in the WD group as compared to disease controls (p < 0.0001). In WD, dilated tips of mitochondrial cristae had a sensitivity of 91% and specificity of 86%, best among EM features. CONCLUSIONS: Light microscopic findings display considerable overlap among children with WD, NAFLD and AIH. Ultrastructural findings of mitochondrial abnormalities are important to distinguish WD from NAFLD and AIH. EM examination should be considered essential in the diagnostic work-up of paediatric liver biopsies.

Pediatric fibromyxoid soft tissue tumor with PLAG1 fusion: A novel entity?

The classification of undifferentiated soft tissue tumors continues to evolve with the expanded application of molecular analysis in clinical practice. We report three cases of a unique soft tissue tumor in young children (5 months to 2 years old) displaying a purely fibromyxoid histology, with positive staining for desmin and CD34. In two cases, RNA sequencing detected a YWHAZ-PLAG1 gene fusion, while in the third case, a previously unreported EEF1A1-PLAG1 fusion was identified. PLAG1 fusions have been reported in several pathologic entities including pleomorphic adenoma, myoepithelial tumors of skin and soft tissue, and lipoblastoma, the latter occurring preferentially in young children. In these tumors, expression of a full length PLAG1 protein comes under the control of the constitutively active promoter of the partner gene in the fusion, and the current cases conform to that model. Overexpression of PLAG1 was confirmed by diffusely positive immunostaining for PLAG1 in all three cases. Our findings raise the possibility of a novel fibromyxoid neoplasm in childhood associated with these rare PLAG1 fusion variants. The only other report of a PLAG1-YWHAZ fusion occurred in a pediatric tumor diagnosed as a "fibroblastic lipoblastoma." This finding raises the possibility of a relationship with our three cases, even though our cases lacked any fat component. Further studies with regard to a shared pathogenesis are required.

Targeted RNA sequencing in the routine clinical detection of fusion genes in salivary gland tumors.

Salivary gland tumors represent a diverse group of neoplasms that occasionally pose a diagnostic challenge for pathologists, particularly with limited sampling. Gene fusions, which may reflect genetic drivers, are increasingly recognized in a subset of these neoplasms, and can be leveraged for diagnostic purposes. We performed a retrospective analysis on a cohort of 80 benign and malignant salivary gland tumors, enriched for subtypes known to harbor recurrent fusion events, to validate the diagnostic use of a targeted RNA sequencing assay to detect fusion transcripts. Testing identified fusion genes in 71% (24/34) of pleomorphic adenoma and carcinoma-ex-pleomorphic adenoma, with 56% of cases showing rearrangement of PLAG1 and 15% HMGA2. In addition to confirming known partners for these genes, novel PLAG1 fusion partners were identified, including DSTN, NTF3, and MEG3; CNOT2 was identified as a novel fusion partner for HMGA2. In adenoid cystic carcinoma, 95% of cases (19/20) were positive for a fusion event. MYB was rearranged in 60% (12/20), MYBL1 in 30% (6/20), and NFIB in 5% (1/20); two tumors exhibited novel fusion products, including NFIB-TBPL1 and MYBL1-VCPIP1. Fusion genes were identified in 64% (9/14) of cases of mucoepidermoid carcinoma; MAML2 was confirmed to partner with either CRTC1 (43%) or CRTC3 (21%). One salivary duct carcinoma was found to harbor a novel RAPGEF6-ACSL6 fusion gene. Finally, as anticipated, gene fusions were not detected in any of the five acinic cell carcinomas included in the cohort. In summary, targeted RNA sequencing represents a diagnostically useful ancillary technique for identifying a variety of existing, and novel, fusion transcripts in the classification of salivary gland neoplasms.

Non-rhabdomyosarcoma soft tissue sarcomas diagnosed in patients at a young age. An overview of clinical, pathological, and molecular findings.

OBJECTIVE: Disease spectrum in pediatric sarcoma differs substantially from adults. We report a cohort of very young children with non-rhabdomyosarcoma soft tissue sarcoma (NRSTS) detailing their molecular features, treatment, and outcome. METHODS: We report features of consecutive children (age <2 years) with NRSTS (2000-2017). Archival pathological material was re-reviewed, with additional molecular techniques applied where indicated. RESULTS: Twenty-nine patients (16 females, 55%) were identified (median age 6 months; range 0-23). Most common diagnoses included infantile fibrosarcoma (IFS, n = 14, 48%), malignant rhabdoid tumor (MRT, n = 4, 14%), and undifferentiated sarcoma (n = 4, 14%). Twenty-seven of 29 (93%) had tumor molecular characterization to confirm diagnosis. Clinical presentation included a swelling/mass (n = 23, 79%). Disease extent was localized (n = 20, 69%), locoregional (n = 6, 21%), or metastatic (n = 3, 10%). Seventeen of 29 (59%) who underwent surgery achieved complete resection (R0). Other treatments included conventional chemotherapy (n = 26, 90%), molecularly targeted therapies (n = 3, 10%), and radiation (n = 5, 17%). At last follow-up (median 3 years; range 0.3-16.4), 23 (79%) were alive, disease-free and six (21%) had died of disease. All patients with IFS were alive and all those with MRT died. A cancer predisposition syndrome (CPS) was confirmed in three of 10 (30%) genetically tested patients. CONCLUSION: We recommend tumor molecular characterization in all young patients including evaluation for CPS to optimize treatment options and prognostication.

Posttransplant Lymphoproliferative Disorder in Children: A 360-degree Perspective.

An earlier incorrect version of this article appeared online. This article was corrected on December 17, 2019.

Clinical Characteristics and Long-term Outcomes of Children With Fibrosing Pancreatitis.

OBJECTIVES: Fibrosing pancreatitis (FP) shares clinical features with autoimmune pancreatitis (AIP), although both entities have not been definitely linked. This study aimed to assess the presence of AIP criteria in an historic FP patient cohort and investigate the clinical features, management, and long-term outcomes of pediatric FP (P-FP). METHODS: Clinical data of 14 P-FP patients from Toronto and 42 P-FP cases from a literature review were collected and compared to pediatric AIP (P-AIP). Toronto P-FP patients were recontacted to assess their current health status using a brief questionnaire. RESULTS: Jaundice and abdominal pain were the symptoms at presentation in 44 of 56 (79%) and 50 of 56 (89%) P-FP patients, respectively. Common findings on cross sectional imaging were an enlarged pancreas head with narrowing of the distal common bile duct (51/54, 94%). Histopathology mainly showed gland fibrosis (39/39, 100%). Three of twelve (25%) P-FP patients had elevated IgG4 in serum. None of the patients were treated with corticosteroids, but some underwent surgical or endoscopic intervention. Toronto patients were followed for a median of 13.6 years (interquartile range: 2.9-22.8). Complications during follow-up included exocrine pancreatic insufficiency (3/14, 21%) and pancreatic gland atrophy (5/13, 38%); but none of the patients had disease relapse or developed diabetes type 3c. Five (5/14, 36%) patients developed other immune-mediated diseases over time. CONCLUSIONS: Clinical features of patients with P-FP resembled those recently described in a subgroup of P-AIP presenting with jaundice. Long-term outcome of these patients is generally good, with or without invasive interventions. As some patients may develop exocrine pancreatic insufficiency and/or other immune-mediated diseases, ongoing clinical monitoring is recommended.

Sirolimus Treatment of an Infant With Intrathoracic Kaposiform Hemangioendothelioma Complicated by Life-threatening Pleural and Pericardial Effusions.

Kaposiform hemangioendothelioma (KHE) is a rare infiltrative vascular tumor that may be associated with Kasabach-Merritt Phenomenon (KMP), which is a consumptive coagulopathy with potentially life-threatening thrombocytopenia. Management of KHE and KMP is challenging, and currently, there are no standardized validated treatment protocols. Mammalian target of rapamycin inhibitors have been shown to be effective in the treatment of KHE. We describe a term male who presented as a diagnostic dilemma with life-threatening pleural and pericardial effusions and severe thrombocytopenia. After extensive work-up the etiology for his condition was determined to be KHE with KMP. The patient was commenced on sirolimus and responded well to therapy with resolution of KMP.

Fetal Sclerotherapy for Hydropic Congenital Cystic Adenomatoid Malformations of the Lung Refractory to Steroids: A Case Report and Review of the Literature.

Microcystic congenital cystic adenomatoid malformations (CCAM), when associated with hydrops, carry a dismal prognosis. Options for treatment are limited and experimental, including antenatal corticosteroids, open fetal surgery, laser ablation and, more recently, sclerotherapy. We describe a case of a large, predominantly microcystic CCAM in a hydropic fetus treated successfully with direct interstitial injection of a sclerosant agent (3% sodium tetradecyl sulfate) at 23+3 weeks gestation, after multiple failed courses of steroids. Elective thoracoscopic right lower lobectomy was performed at 1 year of life and there have been no respiratory or other medical morbidities since. A literature review of fetal lung masses treated with sclerosants antenatally reveals that sclerotherapy may represent a novel treatment option for large hydropic microcystic CCAMs, which are unresponsive to corticosteroids. Further studies are required to evaluate the utility and safety of fetal sclerotherapy, as this may represent an alternative minimally invasive treatment option to fetal lobectomy.

Aggressive embryonal rhabdomyosarcoma in a 3-month-old boy: A clinical and molecular analysis.

Rhabdomyosarcoma (RMS) represents the most common soft tissue sarcoma in the pediatric age group. While RMS has been traditionally classified on the basis of its histological appearance (with embryonal and alveolar being most common), it is now clear that the PAX-FOXO1 fusion product drives prognosis. We report here a case of pelvic embryonal RMS in a 3-month-old male who was subsequently found to have developed brain metastases during the course of chemotherapy. Cytogenetic analysis of the brain metastases at the time of autopsy as well as next-generation sequencing analysis revealed a reciprocal translocation involving the SH3 domain containing ring finger 3 gene (SH3RF3, on chromosome 2q13) and the Lipase C gene (LIPC, on chromosome 15q21.3). Due to the poor quality of the pretreatment and postresection samples, cytogenetics and NGS analysis looking for the presence of this balanced translocation in these specimens could not be performed. To the authors' knowledge, this translocation has never been described in RMS. Further studies are needed to determine the biological and clinical implications of this novel translocation.

Solitary Hepatic Nodule Adjacent to the Right Portal Vein: A Common Finding of Alagille Syndrome?

BACKGROUND: Hepatic lesions have been described in Alagille syndrome (ALGS) in isolated case reports, and most of these have been reported to be hepatocellular carcinoma. OBJECTIVES: The aim of the present study was to determine the frequency, imaging, and histopathologic characteristics of hepatic lesions in children with ALGS. METHODS: Available abdominal imaging of children with ALGS was retrospectively reviewed to note the presence of any focal liver lesion, its location, and imaging characteristics. Other findings including signs of portal hypertension, portal lymph nodes, and splenic and renal abnormalities were also noted. Findings were correlated with pathology in available cases and with clinical follow-up. RESULTS: Of 55 children with clinically and/or genetically confirmed ALGS followed in the liver clinic, 39 (19 boys, 20 girls; mean age 8.9 years) with imaging available on picture archival and communication system were included in the study. Focal hepatic lesions were seen in 12 of the 39 (30%) children, solitary in 11 and multiple in 1. Ten of these children had a large nodule adjacent to the right portal vein. The median diameter of the lesions was 8.1 cm (range 5.6-9.8 cm). Magnetic resonance imaging features and pathology in available cases were suggestive of a regenerative nodule. α-fetoprotein levels were normal in all except 1 child who had mild elevation. CONCLUSIONS: Combining our series and previous case reports, the presence of a large nodule adjacent to the right portal vein appears to be a common finding in ALGS. The typical location, normal α-fetoprotein levels, and magnetic resonance imaging features with vessels coursing through the lesion can reliably differentiate this benign nodule from hepatocellular carcinoma.

Fatal Kawasaki disease with incomplete criteria: Correlation between optical coherence tomography and pathology.

Coronary artery aneurysm is a serious complication of Kawasaki disease (KD). A 3-month-old infant presented with severe KD 27 days after onset of fever. The patient presented with shock, inferolateral ischemia on electrocardiogram and high troponin. Echocardiography showed severe myocardial dysfunction with diffuse coronary dilation and right coronary artery aneurysm. Arterial Doppler demonstrated thrombosis of aneurysmal axillary and iliac arteries. Withdrawal of support was implemented due to multi-organ failure. Post-mortem optical coherence tomography correlated with pathology. The pulmonary artery was normal on OCT and histology. Coronary arteries showed aneurysmal dilatation, with intimal hyperplasia and preserved media on OCT. Pathology confirmed these findings, with destruction of the internal elastic lamina, luminal myofibroblastic proliferation, neovascularization, and partial disappearance of the media. This is the first report of pathologic correlation in KD with OCT at the subacute stage, which adequately identified structural wall changes.