Spindle cell lesions with oncogenic EGFR kinase domain aberrations: expanding the spectrum of protein kinase-related mesenchymal tumors.

EGFR aberrations are reported in a subset of myofibroblastic lesions with kinase domain duplication (EGFR-KDD) and exon 20 mutations being assigned to infantile fibrosarcomas (IFS), mesoblastic nephroma and fibrous hamartoma of infancy (FHI), respectively. In this retrospective study, we correlated molecular findings with histomorphology of 14 myofibroblastic lesions harboring such genetic changes identified by NGS. We additionally performed DNA methylation profiling (DNAmp) and immunohistochemistry. Lesions were from 10 males and 4 females with a mean age of 3 years (range, 0.3 -14) and occurred subcutaneously in the upper limbs (n = 5), lower limbs (n = 3), back/thorax (n = 5), and the nasal cavity (n = 1). Eleven were cured by surgery, including one relapsed case. Two patients were lost to follow-up. One case was very recent, and the patient was biopsied. Histologically, the lesions showed a wide spectrum varying from classic FHI (n=9) to IFS (n=1) or lipofibromatosis-like tumors (LFT-like) (n=2) or dermatofibrosarcoma protuberans-like (DFSP-like) (n=1) to a predominantly-myxoid spindle cell lesion (n=1). Immunohistochemically, all neoplasms stained with CD34, while S100 was positive in 2/14. EGFR expression was observed in 9/10 cases. Molecularly, the IFS and one LFT-like harbored EGFR-KDD, while an exon 20 mutation was identified in all FHI, one LFT-like and in the DFSP-like and predominantly myxoid spindle cell lesion. By DNAmp, all but two cases formed a well-defined cluster, demonstrating that these lesions are also epigenetically related. In conclusion, EGFR kinase domain aberrations found in FHI, IFS, LFT-like, DFSP-like and a spindle cell lesion with a predominant myxoid stroma of children and adolescents show that these neoplasms with a broad morphological spectrum belong to the group of protein kinase-related lesions with a distinct epigenetic signature. Molecular analyses, including DNAmp, help to identify and characterize this emerging category and become mandatory when targeted treatment is considered.

ALK-positive histiocytosis: a new clinicopathologic spectrum highlighting neurologic involvement and responses to ALK inhibition.

ALK-positive histiocytosis is a rare subtype of histiocytic neoplasm first described in 2008 in 3 infants with multisystemic disease involving the liver and hematopoietic system. This entity has subsequently been documented in case reports and series to occupy a wider clinicopathologic spectrum with recurrent KIF5B-ALK fusions. The full clinicopathologic and molecular spectra of ALK-positive histiocytosis remain, however, poorly characterized. Here, we describe the largest study of ALK-positive histiocytosis to date, with detailed clinicopathologic data of 39 cases, including 37 cases with confirmed ALK rearrangements. The clinical spectrum comprised distinct clinical phenotypic groups: infants with multisystemic disease with liver and hematopoietic involvement, as originally described (Group 1A: 6/39), other patients with multisystemic disease (Group 1B: 10/39), and patients with single-system disease (Group 2: 23/39). Nineteen patients of the entire cohort (49%) had neurologic involvement (7 and 12 from Groups 1B and 2, respectively). Histology included classic xanthogranuloma features in almost one-third of cases, whereas the majority displayed a more densely cellular, monomorphic appearance without lipidized histiocytes but sometimes more spindled or epithelioid morphology. Neoplastic histiocytes were positive for macrophage markers and often conferred strong expression of phosphorylated extracellular signal-regulated kinase, confirming MAPK pathway activation. KIF5B-ALK fusions were detected in 27 patients, whereas CLTC-ALK, TPM3-ALK, TFG-ALK, EML4-ALK, and DCTN1-ALK fusions were identified in single cases. Robust and durable responses were observed in 11/11 patients treated with ALK inhibition, 10 with neurologic involvement. This study presents the existing clinicopathologic and molecular landscape of ALK-positive histiocytosis and provides guidance for the clinical management of this emerging histiocytic entity.

Insertion of the CXXC domain of KMT2A into YAP1: An unusual mechanism behind the formation of a chimeric oncogenic protein.

Most neoplasia-associated gene fusions are formed through the fusion of the 5'-part of one gene with the 3'-part of another. We here describe a unique mechanism, by which a part of the KMT2A gene through an insertion replaces part of the YAP1 gene. The resulting YAP1::KMT2A::YAP1 (YKY) fusion was verified by RT-PCR in three cases of sarcoma morphologically resembling sclerosing epithelioid fibrosarcoma (SEF-like sarcoma). In all cases, a portion (exons 4/5-6) encoding the CXXC domain of KMT2A was inserted between exon 4/5 and exon 8/9 of YAP1. The inserted sequence from KMT2A thus replaced exons 5/6-8 of YAP1, which encode an important regulatory sequence of YAP1. To evaluate the cellular impact of the YKY fusion, global gene expression profiles from fresh frozen and formalin-fixed YKY-expressing sarcomas were compared with control tumors. The effects of the YKY fusion, as well as YAP1::KMT2A and KMT2A::YAP1 fusion constructs, were further studied in immortalized fibroblasts. Analysis of differentially upregulated genes revealed significant overlap between tumors and cell lines expressing YKY, as well as with previously reported YAP1 fusions. Pathway analysis of upregulated genes in cells and tumors expressing YKY revealed an enrichment of genes included in key oncogenic signaling pathways, such as Wnt and Hedgehog. As these pathways are known to interact with YAP1, it seems likely that the pathogenesis of sarcomas with the YKY fusion is linked to distorted YAP1 signaling.

GNA11-mutated Sturge-Weber syndrome has distinct neurological and dermatological features.

BACKGROUND AND PURPOSE: Sturge-Weber syndrome (SWS) is a neurocutaneous disorder characterized by clinical manifestations involving the brain, eye and skin. SWS is commonly caused by somatic mutations in G protein subunit Alpha Q (GNAQ). Five cases of subunit Alpha 11 (GNA11) mutations have been reported. We studied phenotypic features of GNA11-SWS and compared them with those of classic SWS. METHODS: Within two European multidisciplinary centers we looked for patients with clinical characteristics of SWS and a GNA11 mutation. Clinical and radiological data were collected retrospectively and prospectively. RESULTS: We identified three patients with SWS associated with a somatic GNA11 mutation. All had disseminated capillary malformation (CM) and hyper- or hypotrophy of an extremity. At birth, the CMs of the face, trunk and limbs were pink and patchy, and slowly darkened with age, evolving to a purple color. Two of the patients had glaucoma. All had neurological symptoms and moderate brain atrophy with a lower degree of severity than that classically associated with SWS. Susceptibility-weighted imaging (SWI) and contrast-enhanced fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging demonstrated the best sensitivity to reveal the pial angiomas. CONCLUSIONS: We have differentiated two distinct clinical/radiological phenotypes of SWS; GNAQ- and GNA11-SWS. The classic GNAQ-SWS is characterized by a homogeneous dark-red CM, commonly associated with underlying soft tissue hypertrophy. The CM in GNA11-SWS is more reticulate and darkens with time, and the neurological picture is milder. SWI and post-contrast FLAIR sequences appear to be necessary to demonstrate leptomeningeal angiomatosis. Anti-epileptic medication or future targeted therapies may be useful, as in classic SWS.

Dermal lipofibromatosis-like neural tumor.

BACKGROUND: Lipofibromatosis-like neural tumor (LPF-NT) is a rare soft tissue typically occurring in the subcutis, characterized by a cellular proliferation of CD34- and S100-protein positive spindle-shaped tumor cells with an infiltrative growth pattern. OBJECTIVE: To describe five cases arising mainly in the dermis in order to expand their morphologic spectrum. METHODS: H&E slides were reviewed, and all cases were stained for CD34, SOX10, S100, ALK, and NTRK1 and some of them with additional staining. RESULTS: Patients were three males and two females with a mean age of 44.8 years (14-68 years). Histopathologically, all cases were characterized by a dense dermal infiltration by monomorphous, mildly atypical, plump to spindle-shaped tumor cells, staining diffusely positive for CD34, S100, and NTRK1 but were negative for S100, EMA, NKIC3, MNF116, SMA, ALK, and desmin. LIMITATIONS: Limited clinical information. CONCLUSION: LPL-NT can be located mainly in the dermis. Sixty percent of our cases showed typical areas of LPL-NT intermingled with more plump cells like the ones in fibrous hamartoma of infancy. We recommend a panel of CD34, S100, and NTRK1 antibodies not only in subcutaneous spindle cell neoplasms but also in the ones predominantly involving the dermis in order to make an accurate diagnosis.

Atypical fibroxanthoma and pleomorphic dermal sarcoma: Is superficial infiltration in subcutaneous tissue acceptable in AFX?

BACKGROUND: Atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) are rare cutaneous neoplasms forming a spectrum. Case reports with recurrences and metastasis have been published despite the current view that AFX is benign. The aim of this study was to identify clinical and histopathological features that predict tumor recurrence. METHODS: A retrospective review of AFX and PDS cases was performed. Clinical characteristics were obtained from patient records. RESULTS: A total of 29 AFX and 23 PDS cases were identified. Review led to re-classification of 12 cases (18%). In 14/50 (26.9%) cases a recurrence occurred. Recurrences were significantly more likely to occur when the tumor showed any infiltration in the subcutaneous fat (100% vs 43.2%, p = 0.000) or when the tumor diameter exceeded 2 cm (46.2% vs 16.2%, p = 0.030). CONCLUSIONS: This study shows that histopathological distinction between AFX and PDS remains difficult with reclassification in 12 out of 52 (18%) cases upon review. All AFX cases solely confined to the dermis behaved benign. We therefore advocate to classify all cases with any form of subcutaneous extension as PDS, and only lesions without as AFX. This contrasts with the current general opinion in which superficial subcutaneous invasion is still accepted in AFX.

Genomic and transcriptomic characterization of desmoplastic small round cell tumors.

Desmoplastic small round cell tumor (DSRCT) is a highly aggressive soft tissue tumor primarily affecting children and young adults. Most cases display a pathognomonic EWSR1-WT1 gene fusion, presumably constituting the primary driver event. Little is, however, known about secondary genetic changes that may affect tumor progression. We here studied 25 samples from 19 DSRCT patients using single nucleotide polymorphism arrays and found that all samples had copy number alterations. The most common imbalances were gain of chromosomes/chromosome arms 1/1q and 5/5p and loss of 6/6q and 16/16q, all occurring in at least eight of the patients. Five cases showed homozygous deletions, affecting a variety of known tumor suppressor genes, for example, CDKN2A and NF1. As almost all patients died of their disease, the impact of individual imbalances on survival could not be evaluated. Global gene expression analysis using mRNA sequencing on fresh-frozen samples from seven patients revealed a distinct transcriptomic profile, with enrichment of genes involved in neural differentiation. Two genes - GJB2 and GAL - that showed higher expression in DSRCT compared to control tumors could be further investigated for their potential as diagnostic markers at the protein level.

Myxoid pleomorphic liposarcoma-a clinicopathologic, immunohistochemical, molecular genetic and epigenetic study of 12 cases, suggesting a possible relationship with conventional pleomorphic liposarcoma.

Myxoid pleomorphic liposarcoma is a recently defined subtype of liposarcoma, which preferentially involves the mediastinum of young patients and shows mixed histological features of conventional myxoid liposarcoma and pleomorphic liposarcoma. While myxoid pleomorphic liposarcoma is known to lack the EWSR1/FUS-DDIT3 fusions characteristic of the former, additional genetic data are limited. To further understand this tumor type, we extensively examined a series of myxoid pleomorphic liposarcomas by fluorescence in situ hybridization (FISH), shallow whole genome sequencing (sWGS) and genome-wide DNA methylation profiling. The 12 tumors occurred in 6 females and 6 males, ranging from 17 to 58 years of age (mean 33 years, median 35 years), and were located in the mediastinum (n = 5), back, neck, cheek and leg, including thigh. Histologically, all cases consisted of relatively, bland, abundantly myxoid areas with a prominent capillary vasculature, admixed with much more cellular and less myxoid foci containing markedly pleomorphic spindled cells, numerous pleomorphic lipoblasts and elevated mitotic activity. Using sWGS, myxoid pleomorphic liposarcomas were found to have complex chromosomal alterations, including recurrent large chromosomal gains involving chromosomes 1, 6-8, 18-21 and losses involving chromosomes 13, 16 and 17. Losses in chromosome 13, in particular loss in 13q14 (including RB1, RCTB2, DLEU1, and ITM2B genes), were observed in 4 out of 8 cases analyzed. Additional FISH analyses confirmed the presence of a monoallelic RB1 deletion in 8/12 cases. Moreover, nuclear Rb expression was deficient in all studied cases. None showed DDIT3 gene rearrangement or MDM2 gene amplification. Using genome-wide DNA methylation profiling, myxoid pleomorphic liposarcomas and conventional pleomorphic liposarcomas formed a common methylation cluster, which segregated from conventional myxoid liposarcomas. While the morphologic, genetic and epigenetic characteristics of myxoid pleomorphic liposarcoma suggest a link with conventional pleomorphic liposarcoma, its distinctive clinical features support continued separate classification for the time being.

Intimal sarcomas and undifferentiated cardiac sarcomas carry mutually exclusive MDM2, MDM4, and CDK6 amplifications and share a common DNA methylation signature.

Undifferentiated mesenchymal tumors arising from the inner lining (intima) of large arteries are classified as intimal sarcomas (ISA) with MDM2 amplification as their molecular hallmark. Interestingly, undifferentiated pleomorphic sarcomas (UPS) of the heart have recently been suggested to represent the cardiac analog of ISA due to morphological overlap and high prevalence of MDM2 amplifications in both neoplasms. However, little is known about ISAs and cardiac UPS without MDM2 amplifications and molecular data supporting their common classification is sparse. Here, we report a series of 35 cases comprising 25 ISAs of the pulmonary artery, one ISA of the renal artery and 9 UPS of the left atrium. Tumors were analyzed utilizing the Illumina Infinium MethylationEPIC BeadChip array, enabling copy number profile generation and unsupervised DNA methylation analysis. DNA methylation patterns were investigated using t-distributed stochastic neighbor embedding (t-SNE) analysis. Histologically, all ISAs and UPS of the left atrium resembled extra-cardiac UPS. All cases exhibited highly complex karyotypes with overlapping patterns between ISA and UPS. 29/35 cases showed mutually exclusive amplifications in the cell-cycle associated oncogenes MDM2 (25/35), MDM4 (2/35), and CDK6 (2/35). We further observed recurrent co-amplifications in PDGFRA (21/35), CDK4 (15/35), TERT (11/35), HDAC9 (9/35), and CCND1 (4/35). Sporadic co-amplifications occurred in MYC, MYCN, and MET (each 1/35). The tumor suppressor CDKN2A/B was frequently deleted (10/35). Interestingly, DNA methylation profiling (t-SNE) revealed an overlap of ISA and cardiac UPS. This "ISA" methylation signature was distinct from potential histologic and molecular mimics. In conclusion, our data reveal MDM4 and CDK6 amplifications in ISAs and UPS of the left atrium, lacking MDM2 amplification. We further report novel co-amplifications of various oncogenes, which may have therapeutic implications. Finally, the genetic and epigenetic concordance of ISAs and UPS of the left atrium further supports a shared pathogenesis and common classification.

Curettage and cryosurgery for enchondroma and atypical cartilaginous tumors of the long bones: Oncological results of a large series.

BACKGROUND AND OBJECTIVES: Intralesional surgical treatment is the preferred therapy for atypical cartilaginous tumors (ACTs) of the long bones in many institutions. However, the literature is still controversial regarding intralesional treatment versus wide resection. Due to the relative rarity of these tumors, studies reporting on the results of intralesional treatment are often small sample studies. METHODS: We retrospectively analyzed the oncological results of 55 enchondromas, 119 ACTs, and 5 chondrosarcomas grade 2 (CS2) treated with curettage and cryosurgery between the years 2004 and 2017 at our institution. The median follow-up period was 53 months (range, 24-169 months). RESULTS: In total, seven cases (three ACT, four CS2) recurred. Residual tumor was detected in 20 cases. Three cases underwent secondary curettage and cryosurgery due to local recurrence. Four cases underwent wide resection and reconstruction due to local recurrence with aggressive imaging characteristics. In total, 20 postoperative complications were seen. CONCLUSION: Curettage and cryosurgery for enchondroma and ACT show very good oncological results with a low recurrence rate and acceptable complication rate. Curettage and cryosurgery is reliable as a surgical treatment for enchondroma and ACT. Further research should define the criteria for determining which specific cartilaginous tumors necessitate surgical treatment.

Loss of H3K27me3 occurs in a large subset of embryonal rhabdomyosarcomas: Immunohistochemical and molecular analysis of 25 cases.

Loss of histone 3 lysine 27 trimethylation (H3K27me3) has been described as a diagnostic marker for malignant peripheral nerve sheath tumor (MPNST), also discriminating MPNST with rhabdomyoblastic differentiation (malignant Triton tumor) from rhabdomyosarcoma (RMS). We studied the immunohistochemical expression of H3K27me3 in embryonal RMSs (ERMSs), performed methylation profiling in order to support the diagnosis and RNA-sequencing for comparison of the transcriptome of H3K27me3-positive and -negative cases. Of the 25 ERMS patients, 17 were males and 8 were females with an age range from 1 to 67 years (median, 6 years). None were known with neurofibromatosis type 1. One patient had Li-Fraumeni syndrome. Tumor localization included paratesticular (n = 9), genitourinary (n = 6), head/neck (n = 5), retroperitoneal (n = 4) and lower arm (n = 1). Five MPNSTs served as reference group. All ERMS had classical features including a variable spindle cell component. Immunohistochemical loss (partial or complete) of H3K27me3 was detected in 18/25 cases (72%). Based on methylation profiling, 22/22 cases were classified as ERMS. Using RNA sequencing, the ERMS group (n = 14) had a distinct gene expression profile in contrast to MPNSTs, confirming that the H3K27me3 negative ERMS cases do not represent malignant Triton tumors. When comparing H3K27me3-negative and -positive ERMSs, gene set enrichment analysis revealed differential expression of genes related to histone acetylation and normal muscle function with H3K27me3 negative ERMSs being associated with acetylation. Conclusion: Loss of H3K27me3 frequently occurs in ERMSs and correlates with H3K27 acetylation. H3K27me3 is not a suitable marker to differentiate ERMS (with spindle cell features) from malignant Triton tumor.

PHF1 fusions cause distinct gene expression and chromatin accessibility profiles in ossifying fibromyxoid tumors and mesenchymal cells.

Ossifying fibromyxoid tumor (OFMT) is a soft tissue tumor frequently displaying gene fusions, most of which affect the PHF1 gene. PHF1 encodes plant homeodomain finger protein 1, which is involved in various processes regulating gene transcription, including those orchestrated by the polycomb repressor complex 2. Here, a series of 37 OFMTs, including 18 typical, 9 atypical, and 10 malignant variants, was analyzed with regard to transcriptomic features, gene fusion and copy number status, and/or single-nucleotide variants. The effects on gene expression and chromatin accessibility of three detected fusions (EP400-PHF1, MEAF6-PHF1, and PHF1-TFE3) were further evaluated in fibroblasts. Genomic imbalances showed a progression-related pattern, with more extensive copy number changes among atypical/malignant lesions than among typical OFMTs; loss of the RB1 gene was restricted to atypical/malignant OFMTs, occurring in one-third of the cases. RNA sequencing identified fusion transcripts in >80% of the cases analyzed, including a novel CSMD1-MEAF6. The gene-expression profile of OFMT was distinct from that of other soft tissue tumors, with extensive transcriptional upregulation of genes in OFMT. These findings were largely recapitulated in gene fusion-expressing fibroblast lines, suggesting that genes involved in, e.g., Wnt signaling and/or being regulated through trimethylation of lysine 27 in histone 3 (H3K27me3) are pivotal for OFMT development. The genes showing differentially higher expression in fusion-expressing cells paralleled increased chromatin accessibility, as revealed by ATAC sequencing. Thus, the present study suggests that OFMT develops through gene fusions that have extensive epigenetic consequences.

Sclerosing epithelioid mesenchymal neoplasm of the pancreas - a proposed new entity.

We have encountered pancreatic tumors with unique histologic features, which do not conform to any of the known tumors of the pancreas or other anatomical sites. We aimed to define their clinicopathologic features and whether they are characterized by recurrent molecular signatures. Eight cases were identified; studied histologically and by immunohistochemistry. Selected cases were also subjected to whole-exome sequencing (WES; n = 4), RNA-sequencing (n = 6), Archer FusionPlex assay (n = 5), methylation profiling using the Illumina MethylationEPIC (850k) array platform (n = 6), and TERT promoter sequencing (n = 5). Six neoplasms occurred in females. The mean age was 43 years (range: 26-75). Five occurred in the head/neck of the pancreas. All patients were treated surgically; none received neoadjuvant/adjuvant therapy. All patients are free of disease after 53 months of median follow-up (range: 8-94). The tumors were well-circumscribed, and the median size was 1.8 cm (range: 1.3-5.8). Microscopically, the unencapsulated tumors had a geographic pattern of epithelioid cell nests alternating with spindle cell fascicles. Some areas showed dense fibrosis, in which enmeshed tumor cells imparted a slit-like pattern. The predominant epithelioid cells had scant cytoplasm and round-oval nuclei with open chromatin. The spindle cells displayed irregular, hyperchromatic nuclei. Mitoses were rare. No lymph node metastases were identified. All tumors were positive for vimentin, CD99 and cytokeratin (patchy), while negative for markers of solid pseudopapillary neoplasm, neuroendocrine, acinar, myogenic/rhabdoid, vascular, melanocytic, or lymphoid differentiation, gastrointestinal stromal tumor as well as MUC4. Whole-exome sequencing revealed no recurrent somatic mutations or amplifications/homozygous deletions in any known oncogenes or tumor suppressor genes. RNA-sequencing and the Archer FusionPlex assay did not detect any recurrent likely pathogenic gene fusions. Single sample gene set enrichment analysis revealed that these tumors display a likely mesenchymal transcriptomic program. Unsupervised analysis (t-SNE) of their methylation profiles against a set of different mesenchymal neoplasms demonstrated a distinct methylation pattern. Here, we describe pancreatic neoplasms with unique morphologic/immunophenotypic features and a distinct methylation pattern, along with a lack of abnormalities in any of key genetic drivers, supporting that these neoplasms represent a novel entity with an indolent clinical course. Given their mesenchymal transcriptomic features, we propose the designation of "sclerosing epithelioid mesenchymal neoplasm" of the pancreas.

Neurofibromatosis-associated malignant peripheral nerve sheath tumors in children have a worse prognosis: A nationwide cohort study.

BACKGROUND: Malignant peripheral nerve sheath tumors (MPNST) are rare and aggressive non-rhabdomyoblastic soft-tissue sarcomas (NRSTS) in children. This study set out to investigate clinical presentation, treatment modalities, and factors associated with survival in pediatric MPNST using Dutch nationwide databases. METHODS: Data were obtained from the Netherlands Cancer Registry (NCR) and the Dutch Pathology Database (PALGA) from 1989 to 2017. All primary MPNSTs were collected. Demographic differences were analyzed between adult and pediatric (age ≤18 years) MPNST. In children, demographic and treatment differences between neurofibromatosis type 1 (NF1) and non-NF1 were analyzed. A Cox proportional hazard model was constructed for localized pediatric MPNSTs. RESULTS: A total of 70/784 MPNST patients were children (37.1% NF1). Children did not present differently from adults. In NF1 children, tumor size was more commonly large (> 5 cm, 92.3% vs 59.1%). Localized disease was primarily resected in 90.6%, and radiotherapy was administered in 37.5%. Non-NF1 children tended to receive chemotherapy more commonly (39.5% vs 26.9%). Overall, estimated five-year survival rates of localized NF1-MPNST was 52.4% (SE: 10.1%) compared with 75.8% (SE: 7.1%) in non-NF1 patients. The multivariate model showed worse survival in NF1 patients (HR: 2.98; 95% CI, 1.17-7.60, P = 0.02) and increased survival in patients diagnosed after 2005 (HR: 0.20; 95% CI, 0.06-0.69, P = 0.01). No treatment factors were independently associated with survival. CONCLUSION: Pediatric MPNSTs have presentations similar to adult MPNSTs. In children, NF1 patients present with larger tumors, but are treated similarly to non-NF1 MPNSTs. In localized pediatric MPNST, NF1 is associated with worse survival. Promisingly, survival has increased for pediatric MPNSTs after 2005.

Treatment of malignant peripheral nerve sheath tumors in pediatric NF1 disease.

BACKGROUND: Malignant peripheral nerve sheath tumors (MPNSTs) are rare yet highly aggressive soft tissue sarcomas. Children with neurofibromatosis type 1 (NF1) have a 10% lifetime risk for development of MPNST. Prognosis remains poor and survival seems worse for NF1 patients. METHODS: This narrative review highlights current practices and pitfalls in the management of MPNST in pediatric NF1 patients. RESULTS: Preoperative diagnostics can be challenging, but PET scans have shown to be useful tools. More recently, functional MRI holds promise as well. Surgery remains the mainstay treatment for these patients, but careful planning is needed to minimize postoperative morbidity. Functional reconstructions can play a role in improving functional status. Radiotherapy can be administered to enhance local control in selected cases, but care should be taken to minimize radiation effects as well as reduce the risk of secondary malignancies. The exact role of chemotherapy has yet to be determined. Reports on the efficacy of chemotherapy vary as some report lower effects in NF1 populations. Promisingly, survival seems to ameliorate in the last few decades and response rates of chemotherapy may increase in NF1 populations when administering it as part of standard of care. However, in metastasized disease, response rates remain poor. New systemic therapies are therefore desperately warranted and multiple trials are currently investigating the role of drugs. Targeted drugs are nevertheless not yet included in first line treatment. CONCLUSION: Both research and clinical efforts benefit from multidisciplinary approaches with international collaborations in this rare malignancy.

Kaposiform hemangioendothelioma and tufted angioma - (epi)genetic analysis including genome-wide methylation profiling.

Kaposiform hemangioendothelioma (KHE) is a locally aggressive vascular condition of childhood and is clinicopathologically related to tufted angioma (TA), a benign skin lesion. Due to their rarity molecular data are scarce. We investigated 7 KHE and 3 TA by comprehensive mutational analysis and genome-wide methylation profiling and compared the clustering, also with vascular malformations. Lesions were from 7 females and 3 males. The age range was 2 months to 9 years with a median of 10 months. KHEs arose in the soft tissue of the thigh (n = 2), retroperitoneum (n = 1), thoracal/abdominal (n = 1), supraclavicular (n = 1) and neck (n = 1). One patient presented with multiple lesions without further information. Two patients developed a Kasabach-Merritt phenomenon. TAs originated in the skin of the shoulder (n = 2) and nose/forehead (n = 1). Of the 5 KHEs and 2 TAs investigated by DNA sequencing, one TA showed a hot spot mutation in NRAS, and one KHE a mutation in RAD50. Unsupervised hierarchical clustering analysis indicated a common methylation pattern of KHEs and TAs, which separated from the homogeneous methylation pattern of vascular malformations. In conclusion, methylation profiling provides further evidence for KHEs and TAs potentially forming a spectrum of one entity. Using next generation sequencing, heterogeneous mutations were found in a subset of cases (2/7) without the presence of GNA14 mutations, previously reported in KHE and TA.

Comprehensive molecular and clinicopathological analysis of vascular malformations: A study of 319 cases.

Vascular malformations are part of overgrowth syndromes characterized by somatic mosaic mutations or rarely by germline mutations. Due to their similarities and diversity, clinicopathological classification can be challenging. A comprehensive targeted Next Generation Sequencing screen using Unique Molecular Identifiers with a technical sensitivity of 1% mutant alleles was performed for frequently mutated positions in ≥21 genes on 319 formalin-fixed paraffin-embedded samples. In 132 out of 319 cases pathogenic mosaic mutations were detected affecting genes previously linked to vascular malformations e.g. PIK3CA (n=80), TEK (TIE2) (n=11), AKT1 (n=1), GNAQ (n=7), GNA11 (n=4), IDH1 (n=3), KRAS (n=9), and NRAS (n=1). Six cases harbored a combination of mutations in PIK3CA and in GNA11 (n=2), GNAQ (n=2), or IDH1 (n=2). Aberrations in PTEN and RASA1 with a variant allele frequency approaching 50% suggestive of germline origin were identified in six out of 102 cases tested; four contained a potential second hit at a lower allele frequency. Ninety-one of the total 142 pathogenic mutations were present at a variant allele frequency <10% illustrating the importance of sensitive molecular analysis. Clinicopathological characteristics showed a broad spectrum and overlap when correlated with molecular data. Sensitive screening of recurrently mutated genes in vascular malformations may help to confirm the diagnosis and reveals potential therapeutic options with a significant contribution of PIK3CA/mTOR and RAS-MAPK pathway mutations. The co-existence of two activating pathogenic mutations in parallel pathways illustrates potential treatment challenges and underlines the importance of multigene testing. Detected germline mutations have major clinical impact.

Calcifying fibrous tumor and inflammatory myofibroblastic tumor are epigenetically related: A comparative genome-wide methylation study.

Based on histological findings, calcifying fibrous tumor (CFT) may be a late (burned out) stage of inflammatory myofibroblastic tumor (IMT). This concept, however, has not been proven by molecular means. Five CFTs were analyzed for IMT-related rearrangements in ALK, ROS1 and RET using fluorescence in situ hybridization (FISH). Additionally, genome-wide methylation patterns were investigated and compared with IMT (n = 7), leiomyoma (n = 7), angioleiomyoma (n = 9), myopericytoma (n = 7) and reactive soft tissue lesions (n = 10) using unsupervised hierarchical cluster analysis and t distributed stochastic neighbor embedding. CFT patients, 4 females and 1 male, had a median age of 20 years ranging from 7 to 43 years. Two patients were younger than 18 years old. The tumors originated in the abdomen (n = 4) and axilla (n = 1). Histologically, all lesions were (multi) nodular and hypocellular consisting of bland looking (myo)fibroblasts embedded in a collagenous matrix with calcifications. FISH analysis brought up negative results for ALK, RET and ROS1 rearrangements. However, genome-wide methylation analysis revealed overlapping methylation patterns of CFT and IMT forming a distinct homogeneous methylation cluster with exception of one case clustering with myopericytoma/angioleiomyoma. In conclusion, DNA methylation profiling supports the concept that CFT and IMT represent both ends of a spectrum of one entity with CFT being the burn out stage of IMT.

A clinicopathological study and prognostic factor analysis of 177 salivary duct carcinoma patients from The Netherlands.

Salivary duct carcinoma (SDC) is a subtype of salivary gland cancer with a dismal prognosis and a need for better prognostication and novel treatments. The aim of this national cohort study was to investigate clinical outcome, prognostic factors, androgen receptor (AR) and human epidermal growth factor receptor 2 (HER2) expression. SDC patients diagnosed between 1990 and 2014 were identified by the Nationwide Network and Registry of Histo- and Cytopathology in the Netherlands (PALGA). Subsequently, medical records were evaluated and pathological diagnoses reviewed. Data were analyzed for overall survival (OS), disease-free survival (DFS), distant metastasis-free survival (DMFS) and prognostic factors. AR was evaluated by immunohistochemistry (IHC), HER2 by IHC and fluorescent in-situ hybridization. A total of 177 patients were included. The median age was 65 years, 75% were male. At diagnosis, 68% presented with lymph node metastases and 6% with distant metastases. Median OS, DFS and DMFS were 51, 23 and 26 months, respectively. In patients presenting without distant metastases, the absolute number of positive lymph nodes was associated with poor OS and DMFS in a multivariable analysis. AR and HER2 were positive in 161/168 (96%) and 44/153 (29%) tumors, respectively, and were not prognostic factors. SDC has a dismal prognosis with primary lymph node involvement in the majority of patients. The absolute number of lymph node metastases was found to be the only prognostic factor for DMFS and OS. AR expression and-to a lesser extent-HER2 expression hold promise for systemic treatment in the metastatic and eventually adjuvant setting.

Array-based DNA-methylation profiling in sarcomas with small blue round cell histology provides valuable diagnostic information.

Undifferentiated solid tumors with small blue round cell histology and expression of CD99 mostly resemble Ewing sarcoma. However, they also may include other tumors such as mesenchymal chondrosarcoma, synovial sarcoma, or small cell osteosarcoma. Definitive classification usually requires detection of entity-specific mutations. While this approach identifies the majority of Ewing sarcomas, a subset of lesions remains unclassified and, therefore, has been termed "Ewing-like sarcomas" or small blue round cell tumors not otherwise specified. We developed an approach for further characterization of small blue round cell tumors not otherwise specified using an array-based DNA-methylation profiling approach. Data were analyzed by unsupervised clustering and t-distributed stochastic neighbor embedding analysis and compared with a reference methylation data set of 460 well-characterized prototypical sarcomas encompassing 18 subtypes. Verification was performed by additional FISH analyses, RNA sequencing from formalin-fixed paraffin-embedded material or immunohistochemical marker analyses. In a cohort of more than 1,000 tumors assumed to represent Ewing sarcomas, 30 failed to exhibit the typical EWS translocation. These tumors were subjected to methylation profiling and could be assigned to Ewing sarcoma in 14 (47%), to small blue round cell tumors with CIC alteration in 6 (20%), to small blue round cell tumors with BCOR alteration in 4 (13%), to synovial sarcoma and to malignant rhabdoid tumor in 2 cases each. One single case each was allotted to mesenchymal chondrosarcoma and adamantinoma. 12/14 tumors classified as Ewing sarcoma could be verified by demonstrating either a canonical EWS translocation evading initial testing, by identifying rare breakpoints or fusion partners. The methylation-based assignment of the remaining small blue round cell tumors not otherwise specified also could be verified by entity-specific molecular alterations in 13/16 cases. In conclusion, array-based DNA-methylation analysis of undifferentiated tumors with small blue round cell histology is a powerful tool for precisely classifying this diagnostically challenging tumor group.