Nuclear factor-κB activation by transforming growth factor-ß1 drives tumour microenvironment-mediated drug resistance in neuroblastoma.

BACKGROUND: Intrinsic and extrinsic factors in the tumour microenvironment (TME) contribute to therapeutic resistance. Here we demonstrate that transforming growth factor (TGF)-ß1 produced in the TME increased drug resistance of neuroblastoma (NB) cells. METHODS: Human NB cell lines were tested in vitro for their sensitivity to Doxorubicin (DOX) and Etoposide (ETOP) in the presence of tumour-associated macrophages (TAM) and mesenchymal stromal cells/cancer-associated fibroblasts (MSC/CAF). These experiments were validated in xenotransplanted and primary tumour samples. RESULTS: Drug resistance was associated with an increased expression of efflux transporter and anti-apoptotic proteins. Upregulation was dependent on activation of nuclear factor (NF)-κB by TGF-ß-activated kinase (TAK1) and SMAD2. Resistance was reversed upon pharmacologic and genetic inhibitions of NF-κB, and TAK1/SMAD2. Interleukin-6, leukaemia inhibitory factor and oncostatin M were upregulated by this TGF-ß/TAK1/NF-κB/SMAD2 signalling pathway contributing to drug resistance via an autocrine loop activating STAT3. An analysis of xenotransplanted NB tumours revealed an increased presence of phospho (p)-NF-κB in tumours co-injected with MSC/CAF and TAM, and these tumours failed to respond to Etoposide but responded if treated with a TGF-ßR1/ALK5 inhibitor. Nuclear p-NF-κB was increased in patient-derived tumours rich in TME cells. CONCLUSIONS: The data provides a novel insight into a targetable mechanism of environment-mediated drug resistance.

Comparative Clinicopathologic and Genomic Analysis of Hepatocellular Neoplasm, Not Otherwise Specified, and Hepatoblastoma.

Accurate diagnosis and treatment of hepatocellular neoplasm, not otherwise specified (HCN-NOS), poses significant challenges. Our study aimed to investigate the clinicopathologic and genomic similarities and differences between HCN-NOS and hepatoblastoma (HB) to guide diagnostic and treatment strategies. The clinicopathologic characteristics of 16 patients with HCN-NOS and 23 patients with HB were compared. Molecular studies, including the OncoKids DNA- and RNA-based next-generation sequencing panel, chromosomal microarray, and targeted Sanger sequencing analyses of CTNNB1 and TERT promoters, were employed. We found that patients with HCN-NOS were older (P < .001) and more frequently classified as high risk (P < .01), yet they showed no significant differences in alpha fetoprotein levels or survival outcomes compared with those with HB. HCN-NOS and HB had a comparable frequency of sequence variants, with CTNNB1 mutations being predominant in both groups. Notably, TERT promoter mutations (37.5%) and rare clinically significant variants (BRAF, NRAS, and KMT2D) were exclusive to HCN-NOS. HCN-NOS demonstrated a higher prevalence of gains in 1q, encompassing the MDM4 locus (17/17 vs 11/24; P < .001), as well as loss/loss of heterozygosity (LOH) of 1p (11/17 vs 6/24; P < .05) and chromosome 11 (7/17 vs 1/24; P < .01) when compared with HB. Furthermore, the recurrent loss/LOH of chromosomes 3, 4p, 9, 15q, and Y was only observed in HCN-NOS. However, no significant differences were noted in gains of chromosomes 2, 8, and 20, or loss/LOH of 4q and 11p between the 2 groups. Notably, no clinically significant gene fusions were detected in either group. In conclusion, our study reveals that HCN-NOS exhibits high-risk clinicopathologic features and greater structural complexity compared with HB. However, patients with HCN-NOS exhibit comparable alpha fetoprotein levels at diagnosis, CTNNB1 mutation rates, and survival outcomes when subjected to aggressive treatment, as compared with those with HB. These findings have the potential to enhance diagnostic accuracy and inform more effective treatments for HCN-NOS.

Norepinephrine transporter and vesicular monoamine transporter 2 tumor expression as a predictor of response to 131 I-MIBG in patients with relapsed/refractory neuroblastoma.

BACKGROUND: Prior studies suggest that norepinephrine transporter (NET) and vesicular monoamine transporter 2 (VMAT2) mediate meta-iodobenzylguanidine (MIBG) uptake and retention in neuroblastoma tumors. We evaluated the relationship between NET and VMAT2 tumor expression and clinical response to 131 I-MIBG therapy in patients with neuroblastoma. METHODS: Immunohistochemistry (IHC) was used to evaluate NET and VMAT2 protein expression levels on archival tumor samples (obtained at diagnosis or relapse) from patients with relapsed or refractory neuroblastoma treated with 131 I-MIBG. A composite protein expression H-score was determined by multiplying a semi-quantitative intensity value (0-3+) by the percentage of tumor cells expressing the protein. RESULTS: Tumor samples and clinical data were available for 106 patients, of whom 28.3% had partial response (PR) or higher. NET H-score was not significantly associated with response (≥PR), though the percentage of tumor cells expressing NET was lower among responders (median 80% for ≥PR vs. 90% for

Use of Surgical Adjuvants Does Not Decrease Recurrence of Aneurysmal Bone Cysts in Surgical Intervention With Pediatric Patients.

BACKGROUND: Aneurysmal bone cysts (ABCs) are benign active tumors often requiring intralesional curettage with or without adjuvants. The primary aim of this study was to analyze whether recurrence is influenced by the use of surgical adjuvants in pediatric patients with ABCs. Secondary aims examined recurrence rates based on age, sex, and physeal contact. METHODS: A retrospective review was performed at a tertiary pediatric hospital from 2004 to 2020. Inclusion criteria consisted of patients treated surgically for histologically confirmed ABCs with a minimum of 6 months follow-up. Patients with treatment for a recurrent tumor or incomplete records were excluded. Patient demographics, location of the lesion, treatment technique, and incidence of recurrence were collected. Statistical analyses were performed using STATA. RESULTS: There were 129 patients (74 males and 55 females) with a mean age of 11.5 ± 4.1 years and an average follow-up of 29.0 ± 25.4 months. The most common locations for ABCs were the femur and tibia. Of the patients, 53.5% had tumors abutting the physis, 28.7% had no physeal contact, and 17.8% had insufficient imaging to evaluate physeal contact. Surgical adjuvants (high-speed burr, coagulation, liquid nitrogen, and/or hydrogen peroxide) were used in 91 of the 129 cases (70.5%). There was no significant difference in recurrence when comparing those who received an adjuvant and those who did not (25.3% vs 23.7%, P = 1.000). Physeal contact was also not significantly associated with recurrence ( P = 0.146). Finally, patients younger than 6 years old were significantly more likely to have recurrence compared with those 6 years old or older (66.7% vs 21.7%, P = 0.007). CONCLUSION: Our study found no association between the use of surgical adjuvants and the risk of recurrence after intralesional curettage for ABCs. Although our study did demonstrate that patients 6 years old or younger had an increased rate of recurrence, no significant association was found regarding physeal contact or sex. These data indicate that surgical adjuvant may not affect the recurrence rates of pediatric patients with ABCs. LEVEL OF EVIDENCE: Level III. This retrospective review compares rates of recurrence based on the choice of surgical adjuvant.

Intraoperative Diagnosis for Pediatric Brain Tumors.

Central nervous system (CNS) tumors are now the most common type of solid tumor in individuals aged 0-19 years, with an incidence rate in the United States around 5 per 100,000, accounting for about 1 out of 4 childhood cancers. Pediatric pathologists encounter brain tumor cases with varying frequency, but many of these encounters begin in the context of intraoperative consultation or "frozen section." This review provides an overview of the technical aspects of intraoperative consultation specific to, or more helpful in, CNS tumors, emphasizing helpful cytologic and histologic features of the more commonly encountered pediatric CNS tumors, and illustrating some common diagnostic pitfalls and how these may be avoided.

PLAG1 Immunohistochemical Staining Is a Surrogate Marker for PLAG1 Fusions in Lipoblastomas.

BACKGROUND: The hallmark of lipoblastoma is a PLAG1 fusion. PLAG1 protein overexpression has been reported in sporadic PLAG1-rearranged lipoblastomas. METHODS: We evaluated the utility of PLAG1 immunohistochemical staining (IHC) in 34 pediatric lipomatous tumors, correlating the results with histology and conventional cytogenetics, FISH and/or next generation sequencing (NGS) results. RESULTS: The study included 24 lipoblastomas, divided into 2 groups designated as "Lipoblastoma 1" with both lipoblastoma histology and PLAG1 rearrangement (n = 16) and "Lipoblastoma 2" with lipoblastoma histology but without PLAG1 cytogenetic rearrangement (n = 8), and 10 lipomas with neither lipoblastoma histology nor a PLAG1 rearrangement. Using the presence of a fusion as the "gold standard" for diagnosing lipoblastoma (Lipoblastoma 1), the sensitivity of PLAG1 IHC was 94%. Using histologic features alone (Lipoblastoma 1 + 2), the sensitivity was 96%. Specificity, as defined by the ability to distinguish lipoma from lipoblastoma, was 100%, as there were no false positives in the lipoma group. CONCLUSIONS: Cytogenetics/molecular testing is expensive and may not be ideal for detecting PLAG1 fusions because PLAG1 fusions are often cytogenetically cryptic and NGS panels may not include all partner genes. PLAG1 IHC is an inexpensive surrogate marker of PLAG1 fusions and may be useful in distinguishing lipoblastomas from lipomas.

Asparagine plays a critical role in regulating cellular adaptation to glutamine depletion.

Many cancer cells consume large quantities of glutamine to maintain TCA cycle anaplerosis and support cell survival. It was therefore surprising when RNAi screening revealed that suppression of citrate synthase (CS), the first TCA cycle enzyme, prevented glutamine-withdrawal-induced apoptosis. CS suppression reduced TCA cycle activity and diverted oxaloacetate, the substrate of CS, into production of the nonessential amino acids aspartate and asparagine. We found that asparagine was necessary and sufficient to suppress glutamine-withdrawal-induced apoptosis without restoring the levels of other nonessential amino acids or TCA cycle intermediates. In complete medium, tumor cells exhibiting high rates of glutamine consumption underwent rapid apoptosis when glutamine-dependent asparagine synthesis was suppressed, and expression of asparagine synthetase was statistically correlated with poor prognosis in human tumors. Coupled with the success of L-asparaginase as a therapy for childhood leukemia, the data suggest that intracellular asparagine is a critical suppressor of apoptosis in many human tumors.

More Than Meets the Eye? A Cautionary Tale of Malignant Ectomesenchymoma Treated as Low-risk Orbital Rhabdomyosarcoma.

Malignant ectomesenchymoma (MEM) is a rare multiphenotypic tumor comprised of mesenchymal and neuroectodermal components. MEM is typically diagnosed in infants and younger children and outcomes are variable. The current approach for treating MEM includes targeting the more aggressive mesenchymal component of the tumor, which is often rhabdomyosarcoma. Here, we describe a case of an orbital tumor initially diagnosed and treated as low-risk rhabdomyosarcoma. Local failure prompting a second biopsy revealed neuronal differentiation consistent with a diagnosis of MEM. Intensifying therapy and local radiotherapy led to a long-term cure. This case offers a cautionary tale that while outcomes for MEM were similar to matched rhabdomyosarcoma cohorts when treated on conventional Intergroup Rhabdomyosarcoma Study Group (IRSG) III/IV protocols, treating MEM using a decreased intensity low-risk rhabdomyosarcoma regimen may not be sufficient.

Relationship of DNA methylation to mutational changes and transcriptional organization in fusion-positive and fusion-negative rhabdomyosarcoma.

Our previous study of DNA methylation in the pediatric soft tissue tumor rhabdomyosarcoma (RMS) demonstrated that fusion-positive (FP) and fusion-negative (FN) RMS tumors exhibit distinct DNA methylation patterns. To further examine the significance of DNA methylation differences in RMS, we investigated genome-wide DNA methylation profiles in discovery and validation cohorts. Unsupervised analysis of DNA methylation data identified novel distinct subsets associated with the specific fusion subtype in FP RMS and with RAS mutation status in FN RMS. Furthermore, the methylation pattern in normal muscle is most similar to the FN subset with wild-type RAS mutation status. Several biologically relevant genes were identified with methylation and expression differences between the two fusion subtypes of FP RMS or between the RAS wild-type and mutant subsets of FN RMS. Genomic localization studies showed that promoter and intergenic regions were hypomethylated and the 3' untranslated regions were hypermethylated in FP compared to FN tumors. There was also a significant difference in the distribution of PAX3-FOXO1 binding sites between genes with and without differential methylation. Moreover, genes with PAX3-FOXO1 binding sites and promoter hypomethylation exhibited the highest frequency of overexpression in FP tumors. Finally, a comparison of RMS model systems revealed that patient-derived xenografts most closely recapitulate the DNA methylation patterns found in human RMS tumors compared to cell lines and cell line-derived xenografts. In conclusion, these findings highlight the interaction of epigenetic changes with mutational alterations and transcriptional organization in RMS tumors, and contribute to improved molecular categorization of these tumors.

Systemic manifestations of extraskeletal myxoid chondrosarcoma associated with a novel t(2;22)(q34;q12) EWS translocation in a child and a review of the literature.

Extraskeletal myxoid chondrosarcoma (EMC), a soft-tissue sarcoma with unique clinicopathologic features and characteristic chromosomal translocations, is extremely rare in the pediatric population. We, herein, present the case of a 7-year-old boy with profound microcytic hypochromic anemia, poor weight gain and a mid-thoracic paraspinal mass that was identified as EMC. Systemic manifestations of localized, nonmetastatic EMC have never been described in the pediatric population, yet our patient's anemia and poor weight gain resolved after successful surgical resection of the tumor, suggesting that localized EMC can present with systemic manifestations. The tumor also contained a novel t(2;22)(q34;q12) translocation involving the EWSR1 gene, which is consistent with additional reports suggesting that a growing list of translocations can drive formation of, and potential new management strategies for, EMC.

Assessment of programmed death-ligand 1 expression and tumor-associated immune cells in pediatric cancer tissues.

BACKGROUND: Programmed death 1 (PD-1) signaling in the tumor microenvironment dampens immune responses to cancer, and blocking this axis induces antitumor effects in several malignancies. Clinical studies of PD-1 blockade are only now being initiated in pediatric patients, and little is known regarding programmed death-ligand 1 (PD-L1) expression in common childhood cancers. The authors characterized PD-L1 expression and tumor-associated immune cells (TAICs) (lymphocytes and macrophages) in common pediatric cancers. METHODS: Whole slide sections and tissue microarrays were evaluated by immunohistochemistry for PD-L1 expression and for the presence of TAICs. TAICs were also screened for PD-L1 expression. RESULTS: Thirty-nine of 451 evaluable tumors (9%) expressed PD-L1 in at least 1% of tumor cells. The highest frequency histotypes comprised Burkitt lymphoma (80%; 8 of 10 tumors), glioblastoma multiforme (36%; 5 of 14 tumors), and neuroblastoma (14%; 17 of 118 tumors). PD-L1 staining was associated with inferior survival among patients with neuroblastoma (P = .004). Seventy-four percent of tumors contained lymphocytes and/or macrophages. Macrophages were significantly more likely to be identified in PD-L1-positive versus PD-L1-negative tumors (P < .001). CONCLUSIONS: A subset of diagnostic pediatric cancers exhibit PD-L1 expression, whereas a much larger fraction demonstrates infiltration with tumor-associated lymphocytes. PD-L1 expression may be a biomarker for poor outcome in neuroblastoma. Further preclinical and clinical investigation will define the predictive nature of PD-L1 expression in childhood cancers both at diagnosis and after exposure to chemoradiotherapy. Cancer 2017;123:3807-3815. © 2017 American Cancer Society.

Fetal Lymphatic Malformations: More Variable Than We Think?

Lymphatic malformations are benign lesions that result from abnormal development of the lymphatic and venous systems. These lesions may be detected during routine prenatal ultrasound screening, and typically demonstrate imaging findings of a multiseptate cystic lesion lacking solid components, vascularity, and calcifications. We report 73 cases of prenatally detected lymphatic malformations and describe greater variability in their prenatal sonographic appearance than previously reported, including purely cystic lesions and mixed cystic and solid lesions with calcifications. Appreciation of this increased variability is important in providing accurate prenatal diagnosis, counseling, and management.

Multimodality imaging findings of massive ovarian edema in children.

BACKGROUND: Massive ovarian edema is a rare benign condition that predominantly affects childbearing women as well as preadolescent girls. It is thought to result from intermittent or partial torsion of the ovary compromising the venous and lymphatic drainage but with preserved arterial supply. The clinical features of massive ovarian edema are nonspecific and can simulate tumors, leading to unnecessary oophorectomy. OBJECTIVE: To demonstrate imaging features that should alert radiologists to consider the diagnosis of massive ovarian edema preoperatively so that fertility-sparing surgery may be considered. MATERIALS AND METHODS: We identified five girls diagnosed with massive ovarian edema at pathology. Presenting symptoms, sidedness, imaging appearance, preoperative diagnosis, and operative and histopathological findings were reviewed. RESULTS: Age range was 9.6-14.3 years (mean age: 12.5 years). Common imaging findings included ovarian enlargement with edema of the stroma, peripherally placed follicles, isointense signal on T1-W MRI and markedly hyperintense signal on T2-W MRI, preservation of color Doppler flow by US, and CT Hounsfield units below 40. The uterus was deviated to the affected side in all patients. Two of the five patients had small to moderate amounts of free pelvic fluid. Mean ovarian volume on imaging was 560 mL (range: 108-1,361 mL). CONCLUSION: While the clinical presentation of massive ovarian edema is nonspecific, an enlarged ovary with stromal edema, peripherally placed follicles and preservation of blood flow may be suggestive and wedge biopsy should be considered intraoperatively to avoid unnecessary removal of the ovary.

Giant hepatic regenerative nodules in Alagille syndrome.

BACKGROUND: Children with Alagille syndrome undergo surveillance radiologic examinations as they are at risk for developing cirrhosis and hepatocellular carcinoma. There is limited literature on the imaging of liver masses in Alagille syndrome. We report the ultrasound (US) and magnetic resonance imaging (MRI) appearances of incidental benign giant hepatic regenerative nodules in this population. OBJECTIVE: To describe the imaging findings of giant regenerative nodules in patients with Alagille syndrome. MATERIALS AND METHODS: A retrospective search of the hospital database was performed to find all cases of hepatic masses in patients with Alagille syndrome during a 10-year period. Imaging, clinical charts, laboratory data and available pathology were reviewed and analyzed and summarized for each patient. RESULTS: Twenty of 45 patients with confirmed Alagille syndrome had imaging studies. Of those, we identified six with giant focal liver masses. All six patients had large central hepatic masses that were remarkably similar on US and MRI, in addition to having features of cirrhosis. In each case, the mass was located in hepatic segment VIII and imaging showed the mass splaying the main portal venous branches at the hepatic hilum, as well as smaller portal and hepatic venous branches coursing through them. On MRI, signal intensity of the mass was isointense to liver on T1-weighted sequences in four of six patients, but hyperintense on T1 in two of six patients. In all six cases, the mass was hypointense on T2- weighted sequences. The mass post-contrast was isointense to adjacent liver in all phases in five the cases. Five out of six patients had pathological correlation demonstrating preserved ductal architecture confirming the final diagnosis of a regenerative nodule. CONCLUSION: Giant hepatic regenerative nodules with characteristic US and MR features can occur in patients with Alagille syndrome with underlying cirrhosis. Recognizing these lesions as benign giant hepatic regenerative nodules should, thereby, mitigate any need for intervention.

Xanthogranulomatous osteomyelitis of the humerus in a pediatric patient with Alagille syndrome: a case report and literature review.

Xanthogranulomatous osteomyelitis (XO) is an exceedingly rare disease characterized by infiltration of histiocytes and foamy macrophages. Both on gross examination and on radiographs, XO can mimic malignancy. We describe the case of a 5-year-old female with Alagille syndrome who presented with a pathologic fracture of the right humerus. Initial radiographs revealed multiple osteolytic lesions in the distal humerus while MRI showed a large soft tissue mass. Biopsy confirmed the diagnosis of XO, which has hitherto not been described in a patient with Alagille syndrome. The patient was admitted for IV antibiotics and taken to the operating room for an incision and debridement. Tissue cultures were obtained and grew Salmonella. Antibiotic therapy was tapered, and the patient responded to treatment. She was doing well at her 6-month follow-up visit. In the discussion section, we explore how osteopenia and immune dysregulation caused by Alagille syndrome can affect the development of XO. We summarize all previously reported cases of XO and conclude that XO presents as an osteolytic lesion that expands rapidly over the course of a few weeks. We highlight that XO can mimic sarcoma because of its mass effect but can be distinguished radiographically by the presence of surrounding sclerosis. Given the rapid onset of XO, we classify it as an acute osteomyelitis. We discuss how leukemia and Ewing sarcoma can present similarly to acute osteomyelitis. We then emphasize key features that can be used to distinguish these malignancies from acute osteomyelitis.

Histone H3 trimethylation on lysine 27 immunostaining pattern in DICER1-associated tumors.

Background: DICER1-associated tumors are heterogeneous and affect several organs. DICER1-associated primary intracranial sarcoma is associated with histone H3 trimethylation on lysine 27 (H3K27me3) loss in nucleus by immunohistochemistry. Methods: We explored the H3K27me3 immunostaining pattern in other DICER1-associated tumors. Twelve tumors from eleven patients with confirmed DICER1 mutations (sporadic and germline) data from a pancancer next-generation sequencing panel, and four tumors of pleuropulmonary blastoma (PPB) were retrieved from our database and stained with anti-H3K27me3 antibody. Results: The H3K27me3 expression in the nucleus showed heterogeneous mosaic loss in neoplastic Sertoli cell components in three of the five cases of moderately to poorly differentiated Sertoli-Leydig cell tumors. Among two tumors of DICER1-associated primary intracranial sarcoma, one showed complete loss of H3K27me3 in all neoplastic cells, whereas the other showed mosaic loss in the sarcomatous spindle cells. One DICER1-associated tumor with epithelial and mesenchymal differentiation, including pulmonary blastoma and PPB, showed mosaic loss of glandular epithelial and mesenchymal components. Four cases of type II PPB and a single case of type III PPB showed a similar mosaic loss of H3K27me3 staining restricted to large spindle cell components. All other components in all tumors-including Leydig cells; the areas of epithelial, cartilaginous, and rhabdomyomatous differentiation; and all cells of the remaining three cases (one papillary thyroid carcinoma and two cases of PPB type I)-demonstrated retained H3K27me3 staining. Conclusions: H3K27me3 expression is not universally lost in DICER1-associated tumors and thus is not predictive of DICER1 mutation status. The mosaic regional loss of H3K27me3 immunostaining is consistent in PPB type II and III, which can be a helpful diagnostic marker for these tumors and suggests a similarity to DICER1-associated intracranial sarcoma.

An Exome Capture-Based RNA-Sequencing Assay for Genome-Wide Identification and Prioritization of Clinically Important Fusions in Pediatric Tumors.

This study reports the development of an exome capture-based RNA-sequencing assay to detect recurring and novel fusions in hematologic, solid, and central nervous system tumors. The assay used Twist Comprehensive Exome capture with either fresh or formalin-fixed samples and a bioinformatic platform that provides fusion detection, prioritization, and downstream curation. A minimum of 50 million uniquely mapped reads, a consensus read alignment/fusion calling approach using four callers (Arriba, FusionCatcher, STAR-Fusion, and Dragen), and custom software were used to integrate, annotate, and rank the candidate fusion calls. In an evaluation of 50 samples, the number of calls varied substantially by caller, from a mean of 24.8 with STAR-Fusion to 259.6 with FusionCatcher; only 1.1% of calls were made by all four callers. Therefore a filtering and ranking algorithm was developed based on multiple criteria, including number of supporting reads, calling consensus, genes involved, and cross-reference against databases of known cancer-associated or likely false-positive fusions. This approach was highly effective in pinpointing known clinically relevant fusions, ranking them first in 47 of 50 samples (94%). Detection of pathogenic gene fusions in three diagnostically challenging cases highlights the importance of a genome-wide and nontargeted method for fusion detection in pediatric cancer.

Pediatric Sertoli-Leydig Cell Tumors of the Ovary: An Integrated Study of Clinicopathological Features, Pan-cancer-Targeted Next-generation Sequencing and Chromosomal Microarray Analysis From a Single Institution.

Sertoli-Leydig cell tumors (SLCTs) are currently classified into 3 molecular subtypes: DICER1 -mutant (younger patient age), FOXL2 -mutant, and DICER1/FOXL2 -wildtype. However, it is not clear whether all pediatric SLCTs are DICER1 -mutant molecular subtypes and whether other molecular genetic aberrations besides DICER1 are involved in the pathogenesis and prognosis of these tumors. We studied comprehensive data for 8 cases of pediatric SLCTs, including clinicopathological features, pan-cancer-targeted next-generation sequencing/OncoKids panel, and chromosomal microarray analysis, to further analyze the correlation among clinicopathological features, molecular genetic aberrations, and prognosis. The ages of the patients ranged from 4 to 16 years (median, 14 y). Seven cases were moderately differentiated, and one was poorly differentiated with heterologous mesenchymal elements. Two cases had heterologous epithelium or retiform elements. Follow-up was available for all 8 patients (median, 49.5 mo). Seven patients were alive without evidence of recurrence or metastasis, and only case 5 developed metastases (synchronous bilateral pulmonary tumors with rhabdomyosarcomatous differentiation). All 8 tumors were found to harbor somatic hotspot DICER1 mutations, and 5 patients carried germline DICER1 mutations (2 of them had the phenotype of DICER1 syndrome). Together with recent studies, the DICER1 mutation frequency is 100% in pediatric SLCTs (n=27, age≤16 y). Copy number alterations were detected in 3 tumors; the only recurrent copy number alterations was the gain of whole chromosome 6 in case 5 and case 8. This is the first report describing clinicopathological features and molecular alterations in pediatric SLCTs. Our results demonstrate that all pediatric SLCTs belong to the DICER1 -mutant molecular subtype, highlighting that somatic hotspot DICER1 mutation detection has high sensitivity (100%) for the auxiliary diagnosis of pediatric SLCTs (age ≤16 y). Some pediatric SLCTs harbor molecular genetic aberrations other than DICER1 mutation, and their significance needs further study.

A proteogenomic surfaceome study identifies DLK1 as an immunotherapeutic target in neuroblastoma.

Cancer immunotherapies have produced remarkable results in B-cell malignancies; however, optimal cell surface targets for many solid cancers remain elusive. Here, we present an integrative proteomic, transcriptomic, and epigenomic analysis of tumor specimens along with normal tissues to identify biologically relevant cell surface proteins that can serve as immunotherapeutic targets for neuroblastoma, an often-fatal childhood cancer of the developing nervous system. We apply this approach to human-derived cell lines (N=9) and cell/patient-derived xenograft (N=12) models of neuroblastoma. Plasma membrane-enriched mass spectrometry identified 1,461 cell surface proteins in cell lines and 1,401 in xenograft models, respectively. Additional proteogenomic analyses revealed 60 high-confidence candidate immunotherapeutic targets and we prioritized Delta-like canonical notch ligand 1 (DLK1) for further study. High expression of DLK1 directly correlated with the presence of a super-enhancer spanning the DLK1 locus. Robust cell surface expression of DLK1 was validated by immunofluorescence, flow cytometry, and immunohistochemistry. Short hairpin RNA mediated silencing of DLK1 in neuroblastoma cells resulted in increased cellular differentiation. ADCT-701, a DLK1-targeting antibody-drug conjugate (ADC), showed potent and specific cytotoxicity in DLK1-expressing neuroblastoma xenograft models. Moreover, DLK1 is highly expressed in several adult cancer types, including adrenocortical carcinoma (ACC), pheochromocytoma/paraganglioma (PCPG), hepatoblastoma, and small cell lung cancer (SCLC), suggesting potential clinical benefit beyond neuroblastoma. Taken together, our study demonstrates the utility of comprehensive cancer surfaceome characterization and credentials DLK1 as an immunotherapeutic target. Highlights: Plasma membrane enriched proteomics defines surfaceome of neuroblastomaMulti-omic data integration prioritizes DLK1 as a candidate immunotherapeutic target in neuroblastoma and other cancersDLK1 expression is driven by a super-enhancer DLK1 silencing in neuroblastoma cells results in cellular differentiation ADCT-701, a DLK1-targeting antibody-drug conjugate, shows potent and specific cytotoxicity in DLK1-expressing neuroblastoma preclinical models.

Epithelioid sarcoma is associated with a high percentage of SMARCB1 deletions.

SMARCB1 gene alterations were first described in highly malignant rhabdoid tumors of the kidney, brain (atypical teratoid/rhabdoid tumor) and soft tissue. An increasing number of tumors have now shown loss of SMARCB1 protein expression by immunohistochemistry, including the majority of epithelioid sarcomas. However, investigations of SMARCB1 gene alterations in epithelioid sarcoma have produced conflicting results. The aim of this study was to evaluate SMARCB1 status using Sanger sequencing of the coding region and multiplex ligation-dependent probe amplification, a rapid and sensitive method for detecting intragenic deletions and duplications, which has not been used in previous studies. Twenty-one epithelioid sarcomas of both classical and proximal type were selected for SMARCB1 gene testing and SMARCB1 immunohistochemistry. Nineteen of 21 (90%) epithelioid sarcomas were SMARCB1 negative by immunohistochemistry. Twelve of the 19 (63%) had adequate DNA recovery for evaluation. Ten of 12 (83%) tumors showed homozygous deletions of the gene. Two cases showed heterozygous deletions and polymorphisms, but no sequence mutations. These results confirm the high frequency of SMARCB1 deletions in epithelioid sarcoma and show that multiplex ligation-dependent probe amplification is a reliable method for detection of deletions in these cases, which can be performed on formalin-fixed, paraffin-embedded tissue. Given the high percentage of SMARCB1 alterations in epithelioid sarcoma, these findings argue against using SMARCB1 gene deletion as a tool in distinguishing them from malignant rhabdoid tumors.