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.

Subpleural pulmonary cysts in children: Associations beyond Trisomy 21.

BACKGROUND: Small air-filled peripheral subpleural cysts are a well-described feature of pulmonary anatomy at computerized tomographic (CT) scan in children with Trisomy 21, yet only anecdotally described in association with other pathologies. The significance of these cysts is unknown. OBJECTIVE: To investigate and explore the pathogenesis of these subpleural cysts in children. MATERIALS AND METHODS: A retrospective review of 16 cases with subpleural cysts diagnosed on CT chest was performed. The distribution, location, and ancillary CT findings were recorded. Hospital charts were reviewed for clinical details, especially cardiac abnormalities, pulmonary artery hypertension (PAH) and genetic associations. Histopathological and clinical correlative data were recorded. RESULTS: Eleven of the 16 children (69%) were found to have an underlying chromosomal or genetic abnormality, six of whom had Trisomy 21. The remaining 5 of the 16 cases (21%) had miscellaneous disorders without an identifiable genetic basis. The most common co-morbidities were cardiac abnormalities (81%) and PAH (62.5%). Regardless of their underlying etiologies, the cysts were present bilaterally in most cases (14/16, 88%). We observed both the postnatal development and the progression of cysts in our cohort. On long-term follow-up, there were five deaths (31%) and six cases (38%) requiring maintenance oxygen therapy due to chronic hypoxia. Two cases (12.5%) became completely asymptomatic after correction of their underlying abnormalities. CONCLUSION: Subpleural cysts are not exclusive to Trisomy 21 and may be seen in other inherited or acquired causes, likely due to altered alveolar growth. We suspect these cysts are a sign of an underlying developmental disorder with variable clinical effect, especially in children with congenital cardiac disease.

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.

Use of a combined transient elastography and biochemical strategy to determine liver fibrosis in pediatric intestinal failure.

BACKGROUND & AIMS: Non-invasive monitoring of intestinal failure (IF) associated liver disease is an ongoing challenge in children with IF. Our objective was to develop a combined algorithm of clinical, transient elastography (TE) and biochemical parameters to identify liver fibrosis in this population. METHODS: A retrospective cohort study of IF patients followed by our intestinal rehabilitation program between November 2015 to October 2019. Patients with a liver biopsy and TE were included. Demographic and liver function tests were collected. Fibrosis on liver biopsies was graded using the modified Scheuer score. Decision tree based algorithms classified low (F0-F1) versus high (F2-F4) fibrosis scores based on a combination of TE, biochemical and demographic parameters, using 6-fold classification error, sensitivity and specificity cross-validation (CV) scores. RESULTS: 42 patients (74% male, median age 7.6 (4.6; 42.7) months) were evaluated. Median length of PN therapy was 182 (121; 556) days. High fibrosis was present in 40.5% with a median TE of 12.1 (6.7; 12.9) kPa in high fibrosis children. An algorithm, based on cut-off values for TE of 11.3 kPa and AST of 40 U/L, and grouping of the underlying etiology resulted in a correct classification of 88.1% of the pathology scores; with sensitivity 0.82 (95% CI 0.57; 0.96), specificity 0.92 (95% CI 0.74; 0.99), positive predictive value 0.88 (95% CI 0.64; 0.96) and negative predictive value 0.88 (95% CI 0.73; 0.96). The CV classification error was 28.6%, CV sensitivity 72.2% and CV specificity 75.5%. CONCLUSIONS: This algorithm shows promising results that could simplify non-invasive monitoring of liver fibrosis in children with IF. Validation in additional IF cohorts is needed.

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.

PRAME protein expression in DICER1-related tumours.

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

Diverse Oncogenic Fusions and Distinct Gene Expression Patterns Define the Genomic Landscape of Pediatric Papillary Thyroid Carcinoma.

Pediatric papillary thyroid carcinoma (PPTC) is clinically distinct from adult-onset disease. Although there are higher rates of metastasis and recurrence in PPTC, prognosis remains highly favorable. Molecular characterization of PPTC has been lacking. Historically, only 40% to 50% of childhood papillary thyroid carcinoma (PTC) were known to be driven by genomic variants common to adult PTC; oncogenic drivers in the remainder were unknown. This contrasts with approximately 90% of adult PTC driven by a discrete number of variants. In this study, 52 PPTCs underwent candidate gene testing, followed in a subset by whole-exome and transcriptome sequencing. Within these samples, candidate gene testing identified variants in 31 (60%) tumors, while exome and transcriptome sequencing identified oncogenic variants in 19 of 21 (90%) remaining tumors. The latter were enriched for oncogenic fusions, with 11 nonrecurrent fusion transcripts, including two previously undescribed fusions, STRN-RET and TG-PBF. Most fusions were associated with 3' receptor tyrosine kinase (RTK) moieties: RET, MET, ALK, and NTRK3. For advanced (distally metastatic) tumors, a driver variant was described in 91%. Gene expression analysis defined three clusters that demonstrated distinct expression of genes involved in thyroid differentiation and MAPK signaling. Among RET-CCDC6-driven tumors, gene expression in pediatric tumors was distinguishable from that in adults. Collectively, these results show that the genomic landscape of pediatric PTC is different from adult PTC. Moreover, they identify genomic drivers in 98% of PPTCs, predominantly oncogenic fusion transcripts involving RTKs, with a pronounced impact on gene expression. Notably, most advanced tumors were driven by a variant for which targeted systemic therapy exists. SIGNIFICANCE: This study highlights important distinctions between the genomes and transcriptomes of pediatric and adult papillary thyroid carcinoma, with implications for understanding the biology, diagnosis, and treatment of advanced disease in children.

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.

Canadian Consensus for Biomarker Testing and Treatment of TRK Fusion Cancer in Pediatric Patients.

Neurotrophic tyrosine receptor kinase gene fusions (NTRK) are oncogenic drivers present at a low frequency in most tumour types (<5%), and at a higher frequency (>80%) in a small number of rare tumours (e.g., infantile fibrosarcoma [IFS]) and considered mutually exclusive with other common oncogenic drivers. Health Canada recently approved two tyrosine receptor kinase (TRK) inhibitors, larotrectinib (for adults and children) and entrectinib (for adults), for the treatment of solid tumours harbouring NTRK gene fusions. In Phase I/II trials, these TRK inhibitors have demonstrated promising overall response rates and tolerability in patients with TRK fusion cancer who have exhausted other treatment options. In these studies, children appear to have similar responses and tolerability to adults. In this report, we provide a Canadian consensus on when and how to test for NTRK gene fusions and when to consider treatment with a TRK inhibitor for pediatric patients with solid tumours. We focus on three pediatric tumour types: non-rhabdomyosarcoma soft tissue sarcoma/unspecified spindle cell tumours including IFS, differentiated thyroid carcinoma, and glioma. We also propose a tumour-agnostic consensus based on the probability of the tumour harbouring an NTRK gene fusion. For children with locally advanced or metastatic TRK fusion cancer who have either failed upfront therapy or lack satisfactory treatment options, TRK inhibitor therapy should be considered.

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.

Spermatogenesis in pre-pubertal boys with Leydig cell neoplasms suggests paracrine stimulation by testosterone.

INTRODUCTION: Pediatric Leydig cell tumors (LCTs) represent approximately 4% of pre-pubertal testicular tumors and are known to cause precocious puberty secondary to testosterone production. While gonadotropins and testosterone are known to initiate spermatogenesis beginning in puberty, it is yet to be determined if a similar phenomenon is triggered by isolated testosterone production in prepubescent boys. OBJECTIVE: To determine if testicular pathology in pre-pubertal pediatric patients with LCTs exhibit spermatogenesis secondary to paracrine testosterone stimulation. STUDY DESIGN: We reviewed patients who underwent orchiectomy for a testicular tumor from 2003-17. We included patients with LCTs and compared them to children with non-LCT pathology (teratomas and epidermoid cysts). We excluded other pathologies and tumors in pubertal patients. Data were collected on the presence of spermatogenesis on pathology, tumor markers and serum hormone results. RESULTS: Orchiectomy for testicular tumors were completed in 66 patients, of which 20 were included in the non-LCT group and 9 in the LCT group. Two of the 9 LCT patients had bilateral pathology. Age at presentation was 6.3 ± 5.8 years for the non-LCT group vs. 8.4 ± 1.6 years for LCTs (p = 0.261). Spermatogenesis was detected in 7 (64%) LCT specimens vs 2 (10%) non-LCT specimens (p = 0.002). Age of the spermatogenesis patients in the non-LCT group (11.08 ± 2.5 years) was older than LCT ones (8.3 ± 2.0 years), suggesting that spermatogenesis in the non-LCT group may be due to early pubertal development. The summary figure demonstrates spermatogenesis identified in a pre-pubertal LCT patient. DISCUSSION: In this study, pre-pubertal males with LCTs were identified to have pathology evidence of spermatogenesis compared to controls with non-LCT pathology. This represents the first study assessing paracrine testosterone effects on spermatogenesis in pre-pubertal patients with LCTs. In contrast, adult literature on LCTs primarily report on resulting concerns for fertility, gynecomastia and testicular atrophy. CONCLUSION: LCTs can induce spermatogenesis in prepubertal patients. This reinforces the hypothesis that paracrine testosterone signaling plays a role in spermatogenesis. Our findings could help explore novel fertility preservation opportunities in children.

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.

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.