High-resolution array CGH identifies common mechanisms that drive embryonal rhabdomyosarcoma pathogenesis

Genomic profiling of pleomorphic rhabdomyosarcoma reveals a genomic signature distinct from that of embryonal rhabdomyosarcoma

Pleomorphic rhabdomyosarcoma (PRMS) is a rare and highly aggressive sarcoma, occurring mostly in the deep soft tissues of middle-aged adults and showing a variable degree of skeletal muscle differentiation. The diagnosis is challenging as pathologic features overlap with embryonal rhabdomyosarcoma (ERMS), malignant Triton tumor, and other pleomorphic sarcomas. As recurrent genetic alterations underlying PRMS have not been described to date, ancillary molecular diagnostic testing is not useful in subclassification. Herein, we perform genomic profiling of a well-characterized cohort of 14 PRMS, compared to a control group of 23 ERMS and other pleomorphic sarcomas (undifferentiated pleomorphic sarcoma and pleomorphic liposarcoma) using clinically validated DNA-targeted Next generation sequencing (NGS) panels (MSK-IMPACT). The PRMS cohort included eight males and six females, with a median age of 53 years (range 31-76 years). Despite similar tumor mutation burdens, the genomic landscape of PRMS, with a high frequency of TP53 (79%) and RB1 (43%) alterations, stood in stark contrast to ERMS, with 4% and 0%, respectively. CDKN2A deletions were more common in PRMS (43%), compared to ERMS (13%). In contrast, ERMS harbored somatic driver mutations in the RAS pathway and loss of function mutations in BCOR, which were absent in PRMS. Copy number variations in PRMS showed multiple chromosomal arm-level changes, most commonly gains of chr17p and chr22q and loss of chr6q. Notably, gain of chr8, commonly seen in ERMS (61%) was conspicuously absent in PRMS. The genomic profiles of other pleomorphic sarcomas were overall analogous to PRMS, showing shared alterations in TP53, RB1, and CDKN2A. Overall survival and progression-free survival of PRMS were significantly worse (p < 0.0005) than that of ERMS. Our findings revealed that the molecular landscape of PRMS aligns with other adult pleomorphic sarcomas and is distinct from that of ERMS. Thus, NGS assays may be applied in select challenging cases toward a refined classification. Finally, our data corroborate the inclusion of PRMS in the therapeutic bracket of pleomorphic sarcomas, given that their clinical outcomes are comparable.

Sequential genomic analysis using a multisample/multiplatform approach to better define rhabdomyosarcoma progression and relapse

The genomic spectrum of rhabdomyosarcoma (RMS) progression from primary to relapse is not fully understood. In this pilot study, we explore the sensitivity of various targeted and whole-genome NGS platforms in order to assess the best genomic approach of using liquid biopsy in future prospective clinical trials. Moreover, we investigate 35 paired primary/relapsed RMS from two contributing institutions, 18 fusion-positive (FP-RMS) and 17 fusion-negative RMS (FN-RMS) by either targeted DNA or whole exome sequencing (WES). In 10 cases, circulating tumor DNA (ctDNA) from multiple timepoints through clinical care and progression was analyzed for feasibility of liquid biopsy in monitoring treatment response/relapse. ctDNA alterations were evaluated using a targeted 36-gene custom RMS panel at high coverage for single-nucleotide variation and fusion detection, and a shallow whole-genome sequencing for copy number variation. FP-RMS have a stable genome with relapse, with common secondary alterations CDKN2A/B, MYCN, and CDK4 present at diagnosis and impacting survival. FP-RMS lacking major secondary events at baseline acquire recurrent MYCN and AKT1 alterations. FN-RMS acquire a higher number of new alterations, most commonly SMARCA2 missense mutations. ctDNA analyses detect pathognomonic variants in all RMS patients within our collection at diagnosis, regardless of type of alterations, and confirmed at relapse in 86% of FP-RMS and 100% FN-RMS. Moreover, a higher number of fusion reads is detected with increased disease burden and at relapse in patients following a fatal outcome. These results underscore patterns of tumor progression and provide rationale for using liquid biopsy to monitor treatment response.

The Potential for Targeting AVIL and Other Actin-Binding Proteins in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common pediatric soft-tissue cancer with a survival rate below 27% for high-risk children despite aggressive multi-modal therapeutic interventions. After decades of research, no targeted therapies are currently available. Therapeutically targeting actin-binding proteins, although promising, has historically been challenging. Recent advances have made this possibility more salient, including our lab's identification of advillin (AVIL), a novel oncogenic actin-binding protein that plays a role in many cytoskeletal functions. AVIL is overexpressed in many RMS cell lines, patient-derived xenograft models, and a cohort of 30 clinical samples of both the alveolar (ARMS) and embryonal (ERMS) subtypes. Overexpression of AVIL in mesenchymal stem cells induces neoplastic transformation both in vitro and in vivo, and reversing overexpression through genetic modulation reverses the transformation. This suggests a critical role of AVIL in RMS tumorigenesis and maintenance. As an actin-binding protein, AVIL would not traditionally be considered a druggable target. This perspective will address the feasibility of targeting differentially expressed actin-binding proteins such as AVIL therapeutically, and how critical cell infrastructure can be damaged in a cancer-specific manner.

The spectrum of cell death in sarcoma

The balance between cell death and cell survival is a highly coordinated process by which cells break down and remove unnecessary or harmful materials in a controlled, highly regulated, and compartmentalized manner. Cell exposure to various stresses, such as oxygen starvation, a lack of nutrients, or exposure to radiation, can initiate autophagy. Autophagy is a carefully orchestrated process with multiple steps, each regulated by specific genes and proteins. Autophagy proteins impact cellular maintenance and cell fate in response to stress, and targeting this process is one of the most promising methods of anti-tumor therapy. It is currently not fully understood how autophagy affects different types of tumor cells, which makes it challenging to predict outcomes when this process is manipulated. In this review, we will explore the mechanisms of autophagy and investigate it as a potential and promising therapeutic target for aggressive sarcomas.

Identify potential driver genes for PAX-FOXO1 fusion-negative rhabdomyosarcoma through frequent gene co-expression network mining

Background

Rhabdomyosarcoma (RMS) is a soft tissue sarcoma usually originated from skeletal muscle. Currently, RMS classification based on PAX-FOXO1 fusion is widely adopted. However, compared to relatively clear understanding of the tumorigenesis in the fusion-positive RMS, little is known for that in fusion-negative RMS (FN-RMS).

Methods

We explored the molecular mechanisms and the driver genes of FN-RMS through frequent gene co-expression network mining (fGCN), differential copy number (CN) and differential expression analyses on multiple RMS transcriptomic datasets.

Results

We obtained 50 fGCN modules, among which five are differentially expressed between different fusion status. A closer look showed 23% of Module 2 genes are concentrated on several cytobands of chromosome 8. Upstream regulators such as MYC, YAP1, TWIST1 were identified for the fGCN modules. Using in a separate dataset we confirmed that, comparing to FP-RMS, 59 Module 2 genes show consistent CN amplification and mRNA overexpression, among which 28 are on the identified chr8 cytobands. Such CN amplification and nearby MYC (also resides on one of the above cytobands) and other upstream regulators (YAP1, TWIST1) may work together to drive FN-RMS tumorigenesis and progression. Up to 43.1% downstream targets of Yap1 and 45.8% of the targets of Myc are differentially expressed in FN-RMS vs. normal comparisons, which also confirmed the driving force of these regulators.

Discussion

We discovered that copy number amplification of specific cytobands on chr8 and the upstream regulators MYC, YAP1 and TWIST1 work together to affect the downstream gene co-expression and promote FN-RMS tumorigenesis and progression. Our findings provide new insights for FN-RMS tumorigenesis and offer promising targets for precision therapy. Experimental investigation about the functions of identified potential drivers in FN-RMS are in progress.

Case Report: An NTRK1 fusion-positive embryonal rhabdomyosarcoma: clinical presentations, pathological characteristics and genotypic analyses

Rhabdomyosarcoma (RMS) is a prevalent form of soft tissue sarcoma that primarily affects children. Pediatric RMS is characterized by two distinct histological variants: embryonal (ERMS) and alveolar (ARMS). ERMS is a malignant tumor with primitive characteristics resembling the phenotypic and biological features of embryonic skeletal muscles. With the widespread and growing application of advanced molecular biological technologies, such as next-generation sequencing (NGS), it has been possible to determine the oncogenic activation alterations of many tumors. Specifically for soft tissue sarcomas, the determination of tyrosine kinase gene and protein related changes can be used as diagnostic aids and may be used as predictive markers for targeted tyrosine kinase inhibition therapy. Our study reports a rare and exceptional case of an 11-year-old patient diagnosed with ERMS, who tested positive for MEF2D-NTRK1 fusion. The case report presents a comprehensive overview of the clinical, radiographic, histopathological, immunohistochemical, and genetic characteristics of a palpebral ERMS. Furthermore, this study sheds light on an uncommon occurrence of NTRK1 fusion-positive ERMS, which may provide theoretical basis for therapy and prognosis.

Haploinsufficiency of the lysosomal sialidase NEU1 results in a model of pleomorphic rhabdomyosarcoma in mice

Rhabdomyosarcoma, the most common pediatric sarcoma, has no effective treatment for the pleomorphic subtype. Still, what triggers transformation into this aggressive phenotype remains poorly understood. Here we used Ptch1+/-/ETV7TG/+/- mice with enhanced incidence of rhabdomyosarcoma to generate a model of pleomorphic rhabdomyosarcoma driven by haploinsufficiency of the lysosomal sialidase neuraminidase 1. These tumors share mostly features of embryonal and some of alveolar rhabdomyosarcoma. Mechanistically, we show that the transforming pathway is increased lysosomal exocytosis downstream of reduced neuraminidase 1, exemplified by the redistribution of the lysosomal associated membrane protein 1 at the plasma membrane of tumor and stromal cells. Here we exploit this unique feature for single cell analysis and define heterogeneous populations of exocytic, only partially differentiated cells that force tumors to pleomorphism and promote a fibrotic microenvironment. These data together with the identification of an adipogenic signature shared by human rhabdomyosarcoma, and likely fueling the tumor's metabolism, make this model of pleomorphic rhabdomyosarcoma ideal for diagnostic and therapeutic studies.

Canonical Hedgehog Pathway and Noncanonical GLI Transcription Factor Activation in Cancer

The Hedgehog signaling pathway is one of the fundamental pathways required for development and regulation of postnatal regeneration in a variety of tissues. The pathway has also been associated with cancers since the identification of a mutation in one of its components, PTCH, as the cause of Basal Cell Nevus Syndrome, which is associated with several cancers. Our understanding of the pathway in tumorigenesis has expanded greatly since that initial discovery over two decades ago. The pathway has tumor-suppressive and oncogenic functions depending on the context of the cancer. Furthermore, noncanonical activation of GLI transcription factors has been reported in a number of tumor types. Here, we review the roles of canonical Hedgehog signaling pathway and noncanonical GLI activation in cancers, particularly epithelial cancers, and discuss an emerging concept of the distinct outcomes that these modes have on cancer initiation and progression.

Evolving classification of rhabdomyosarcoma

Rhabdomyosarcomas comprise the single largest category of soft tissue sarcomas in children and adolescents in the United States, occurring in 4.5 million people aged below 20 years. Based on the clinicopathological features and genetic abnormalities identified, rhabdomyosarcomas are classified into embryonal, alveolar, spindle cell/sclerosing and pleomorphic subtypes. Each subtype shows distinctive morphology and has characteristic genetic abnormalities. This review discusses the evolution of the classification of rhabdomyosarcoma to the present day, together with a discussion of key histomorphological and genetic features of each subtype and the diagnostic approach to these tumours.

Molecular analysis of 10 pleomorphic rhabdomyosarcomas reveals potential prognostic markers and druggable targets

Pleomorphic rhabdomyosarcoma (PRMS) is a rare and aggressive adult sarcoma with a median overall survival of less than 2 years. Most PRMS do not respond to conventional chemotherapy and/or radiation, and targeted therapies are nonexistent as few PRMS have undergone the molecular characterization necessary to identify therapeutic options. To date, complex structural and few recurrent regional copy alterations have been reported in the PRMS cases evaluated by cytogenetic and comparative genomic hybridization. Thus, there remains an urgent need for more comprehensive molecular profiling to both understand disease pathogenesis and to identify potentially actionable targets. Ten PRMS resection cases were retrieved from institutional archives and clinicopathologic demographics were recorded. All tumors were subjected to DNA-based targeted next-generation sequencing (NGS) of 340 cancer-related genes while a subset (six cases) underwent gene-expression profiling of 770 genes. Alterations identified by NGS included genes involved in cell cycle regulation (90%), the RAS/MAPK and AKT pathways (80%), telomere maintenance (40%), chromatin remodeling (40%), and DNA repair (20%), as well as the cAMP-signaling pathway (10%). Microsatellite instability was absent in all cases, and tumor mutational burden was predominantly low. Gene expression profiling revealed up-regulation of many of the same pathways, including the RTK/MAPK, AKT/PIK3CA/mTOR, Wnt, Hedgehog and JAK/STAT pathways. Survival analysis demonstrated patients with concurrent biallelic inactivation of CDKN2A and TP53 showed significantly shorter overall survival (median: 2 vs. 50 months). Our integrated molecular characterization identified not only potentially targetable alterations, but also prognostic markers for stratification of PRMS patients.

Genetic Characterization, Current Model Systems and Prognostic Stratification in PAX Fusion-Negative vs. PAX Fusion-Positive Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and adolescents and accounts for approximately 2% of soft tissue sarcomas in adults. It is subcategorized into distinct subtypes based on histological features and fusion status (PAX-FOXO1/VGLL2/NCOA2). Despite advances in our understanding of the pathobiological and molecular landscape of RMS, the prognosis of these tumors has not significantly improved in recent years. Developing a better understanding of genetic abnormalities and risk stratification beyond the fusion status are crucial to developing better therapeutic strategies. Herein, we aim to highlight the genetic pathways/abnormalities involved, specifically in fusion-negative RMS, assess the currently available model systems to study RMS pathogenesis, and discuss available prognostic factors as well as their importance for risk stratification to achieve optimal therapeutic management.

Synthetic essentiality between PTEN and core dependency factor PAX7 dictates rhabdomyosarcoma identity

PTEN promoter hypermethylation is nearly universal and PTEN copy number loss occurs in ~25% of fusion-negative rhabdomyosarcoma (FN-RMS). Here we show Pten deletion in a mouse model of FN-RMS results in less differentiated tumors more closely resembling human embryonal RMS. PTEN loss activated the PI3K pathway but did not increase mTOR activity. In wild-type tumors, PTEN was expressed in the nucleus suggesting loss of nuclear PTEN functions could account for these phenotypes. Pten deleted tumors had increased expression of transcription factors important in neural and skeletal muscle development including Dbx1 and Pax7. Pax7 deletion completely rescued the effects of Pten loss. Strikingly, these Pten;Pax7 deleted tumors were no longer FN-RMS but displayed smooth muscle differentiation similar to leiomyosarcoma. These data highlight how Pten loss in FN-RMS is connected to a PAX7 lineage-specific transcriptional output that creates a dependency or synthetic essentiality on the transcription factor PAX7 to maintain tumor identity.

Protein Arginine Methyltransferase (PRMT) Inhibitors-AMI-1 and SAH Are Effective in Attenuating Rhabdomyosarcoma Growth and Proliferation in Cell Cultures

Rhabdomyosarcoma (RMS) is a malignant soft tissue cancer that develops mostly in children and young adults. With regard to histopathology, four rhabdomyosarcoma types are distinguishable: embryonal, alveolar, pleomorphic and spindle/sclerosing. Currently, increased amounts of evidence indicate that not only gene mutations, but also epigenetic modifications may be involved in the development of RMS. Epigenomic changes regulate the chromatin architecture and affect the interaction between DNA strands, histones and chromatin binding proteins, thus, are able to control gene expression. The main aim of the study was to assess the role of protein arginine methyltransferases (PRMT) in the cellular biology of rhabdomyosarcoma. In the study we used two pan-inhibitors of PRMT, called AMI-1 and SAH, and evaluated their effects on proliferation and apoptosis of RMS cells. We observed that AMI-1 and SAH reduce the invasive phenotype of rhabdomyosarcoma cells by decreasing their proliferation rate, cell viability and ability to form cell colonies. In addition, microarray analysis revealed that these inhibitors attenuate the activity of the PI3K-Akt signaling pathway and affect expression of genes related to it.

Molecular mechanisms underpinning sarcomas and implications for current and future therapy

Sarcomas are complex mesenchymal neoplasms with a poor prognosis. Their clinical management is highly challenging due to their heterogeneity and insensitivity to current treatments. Although there have been advances in understanding specific genomic alterations and genetic mutations driving sarcomagenesis, the underlying molecular mechanisms, which are likely to be unique for each sarcoma subtype, are not fully understood. This is in part due to a lack of consensus on the cells of origin, but there is now mounting evidence that they originate from mesenchymal stromal/stem cells (MSCs). To identify novel treatment strategies for sarcomas, research in recent years has adopted a mechanism-based search for molecular markers for targeted therapy which has included recapitulating sarcomagenesis using in vitro and in vivo MSC models. This review provides a comprehensive up to date overview of the molecular mechanisms that underpin sarcomagenesis, the contribution of MSCs to modelling sarcomagenesis in vivo, as well as novel topics such as the role of epithelial-to-mesenchymal-transition (EMT)/mesenchymal-to-epithelial-transition (MET) plasticity, exosomes, and microRNAs in sarcomagenesis. It also reviews current therapeutic options including ongoing pre-clinical and clinical studies for targeted sarcoma therapy and discusses new therapeutic avenues such as targeting recently identified molecular pathways and key transcription factors.

Context-dependent modulation of aggressiveness of pediatric tumors by individual oncogenic RAS isoforms

A prototypic pediatric cancer that frequently shows activation of RAS signaling is embryonal rhabdomyosarcoma (ERMS). ERMS also show aberrant Hedgehog (HH)/GLI signaling activity and can be driven by germline mutations in this pathway. We show, that in ERMS cell lines derived from sporadic tumors i.e. from tumors not caused by an inherited genetic variant, HH/GLI signaling plays a subordinate role, because oncogenic mutations in HRAS, KRAS, or NRAS (collectively named oncRAS) inhibit the main HH target GLI1 via the MEK/ERK-axis, but simultaneously increase proliferation and tumorigenicity. oncRAS also modulate expression of stem cell markers in an isoform- and context-dependent manner. In Hh-driven murine ERMS that are caused by a Patched mutation, oncHRAS and mainly oncKRAS accelerate tumor development, whereas oncNRAS induces a more differentiated phenotype. These features occur when the oncRAS mutations are induced at the ERMS precursor stage, but not when induced in already established tumors. Moreover, in contrast to what is seen in human cell lines, oncRAS mutations do not alter Hh signaling activity and marginally affect expression of stem cell markers. Together, all three oncRAS mutations seem to be advantageous for ERMS cell lines despite inhibition of HH signaling and isoform-specific modulation of stem cell markers. In contrast, oncRAS mutations do not inhibit Hh-signaling in Hh-driven ERMS. In this model, oncRAS mutations seem to be advantageous for specific ERMS populations that occur within a specific time window during ERMS development. In addition, this window may be different for individual oncRAS isoforms, at least in the mouse.

Fibroblast Growth Factor Receptor (FGFR) Signaling in GIST and Soft Tissue Sarcomas

Sarcomas are a heterogeneous group of rare malignancies originating from mesenchymal tissues with limited therapeutic options. Recently, alterations in components of the fibroblast growth factor receptor (FGFR) signaling pathway have been identified in a range of different sarcoma subtypes, most notably gastrointestinal stromal tumors, rhabdomyosarcomas, and liposarcomas. These alterations include genetic events such as translocations, mutations, and amplifications as well as transcriptional overexpression. Targeting FGFR has therefore been proposed as a novel potential therapeutic approach, also in light of the clinical activity shown by multi-target tyrosine kinase inhibitors in specific subtypes of sarcomas. Despite promising preclinical evidence, thus far, clinical trials have enrolled very few sarcoma patients and the efficacy of selective FGFR inhibitors appears relatively low. Here, we review the known alterations of the FGFR pathway in sarcoma patients as well as the preclinical and clinical evidence for the use of FGFR inhibitors in these diseases. Finally, we discuss the possible reasons behind the current clinical data and highlight the need for biomarker stratification to select patients more likely to benefit from FGFR targeted therapies.

Glasdegib in newly diagnosed acute myeloid leukemia

INTRODUCTION

Acute myeloid leukemia (AML) is an aggressive blood cancer that proves fatal for the majority of affected individuals. Older patients are particularly vulnerable due to more unfavorable disease biology and diminished ability to tolerate intensive induction chemotherapy (ICT). Safer, more efficacious therapies are desperately needed.

AREAS COVERED

We briefly summarize the challenges facing AML treatment and introduce the rapidly expanding therapeutic landscape. Our focus is on the Hedgehog (Hh) pathway and how preclinical evidence has spurred the clinical development of selective inhibitors for oncology indications. Glasdegib is the first Hh pathway inhibitor approved for the treatment of a hematologic malignancy, and we review its pharmacology, safety, efficacy, and potential clinical impact in AML patients.

EXPERT OPINION

Advances in the mechanistic understanding of AML have started to translate into improved therapeutic options for patients with contraindications to ICT. Glasdegib improved overall survival in this population when combined with low-dose cytarabine. While an encouraging development for these difficult to treat patients, alternative combination therapy approaches such as venetoclax plus azacitidine have gained greater clinical traction. Further investigation of glasdegib combination strategies and predictive biomarkers, particularly in regard to overcoming chemoresistance and preventing relapse, is needed to better define its clinical utility.

Functional imaging of RAS pathway targeting in malignant peripheral nerve sheath tumor cells and xenografts

BACKGROUND

Malignant peripheral nerve sheath tumor (MPNST) is an aggressive form of soft-tissue sarcoma (STS) in children. Despite intensive therapy, relatively few children with metastatic and unresectable disease survive beyond three years. RAS pathway activation is common in MPNST, suggesting MEK pathway inhibition as a targeted therapy, but the impact on clinical outcome has been small to date.

PROCEDURE

We conducted preclinical pharmacokinetic (PK) and pharmacodynamic studies of two MEK inhibitors, trametinib and selumetinib, in two MPNST models and analyzed tumors for intratumor drug levels. We then investigated 3'-deoxy-3'-[¹⁸ F]fluorothymidine (¹⁸ F-FLT) PET imaging followed by ¹⁸ F-FDG PET/CT imaging of MPNST xenografts coupled to short-term or longer-term treatment with selumetinib focusing on PET-based imaging as a biomarker of MEK inhibition.

RESULTS

Trametinib decreased pERK expression in MPNST xenografts but did not prolong survival or decrease Ki67 expression. In contrast, selumetinib prolonged survival of animals bearing MPNST xenografts, and this correlated with decreased pERK and Ki67 staining. PK studies revealed a significantly higher fraction of unbound selumetinib within a responsive MPNST xenograft model. Thymidine uptake, assessed by ¹⁸ F-FLT PET/CT, positively correlated with Ki67 expression in different xenograft models and in response to selumetinib.

CONCLUSION

The ability of MEK inhibitors to control MPNST growth cannot simply be predicted by serum drug levels or drug-induced changes in pERK expression. Tumor cell proliferation assessed by ¹⁸ F-FLT PET imaging might be useful as an early response marker to targeted therapies, including MEK inhibition, where a primary effect is cell-cycle arrest.

Genetic Predisposition to Solid Pediatric Cancers

Progresses over the past years have extensively improved our capacity to use genome-scale analyses—including high-density genotyping and exome and genome sequencing—to identify the genetic basis of pediatric tumors. In particular, exome sequencing has contributed to the evidence that about 10% of children and adolescents with tumors have germline genetic variants associated with cancer predisposition. In this review, we provide an overview of genetic variations predisposing to solid pediatric tumors (medulloblastoma, ependymoma, astrocytoma, neuroblastoma, retinoblastoma, Wilms tumor, osteosarcoma, rhabdomyosarcoma, and Ewing sarcoma) and outline the biological processes affected by the involved mutated genes. A careful description of the genetic basis underlying a large number of syndromes associated with an increased risk of pediatric cancer is also reported. We place particular emphasis on the emerging view that interactions between germline and somatic alterations are a key determinant of cancer development. We propose future research directions, which focus on the biological function of pediatric risk alleles and on the potential links between the germline genome and somatic changes. Finally, the importance of developing new molecular diagnostic tests including all the identified risk germline mutations and of considering the genetic predisposition in screening tests and novel therapies is emphasized.

Phenotypic profiling with a living biobank of primary rhabdomyosarcoma unravels disease heterogeneity and AKT sensitivity

Cancer therapy is currently shifting from broadly used cytotoxic drugs to patient-specific precision therapies. Druggable driver oncogenes, identified by molecular analyses, are present in only a subset of patients. Functional profiling of primary tumor cells could circumvent these limitations, but suitable platforms are unavailable for most cancer entities. Here, we describe an in vitro drug profiling platform for rhabdomyosarcoma (RMS), using a living biobank composed of twenty RMS patient-derived xenografts (PDX) for high-throughput drug testing. Optimized in vitro conditions preserve phenotypic and molecular characteristics of primary PDX cells and are compatible with propagation of cells directly isolated from patient tumors. Besides a heterogeneous spectrum of responses of largely patient-specific vulnerabilities, profiling with a large drug library reveals a strong sensitivity towards AKT inhibitors in a subgroup of RMS. Overall, our study highlights the feasibility of in vitro drug profiling of primary RMS for patient-specific treatment selection in a co-clinical setting.

Patient-specific precision medicine approaches are important for future cancer therapies. Here, the authors show that functional drug profiling with Rhabdomyosarcoma cells isolated from PDX and primary patient tumors uncovers patient-specific vulnerabilities.

Advanced pharmacological therapies for neurofibromatosis type 1-related tumors

Neurofibromatosis Type 1 (NF1) is an autosomal dominant tumor-predisposition disorder that is caused by a heterozygous loss of function variant in the NF1 gene, which encodes a protein called neurofibromin. The absence of neurofibromin causes increased activity in the Rat sarcoma protein (RAS) signalling pathway, which results in an increased growth and cell proliferation. As a result, both oncological and non-oncological comorbidities contribute to a high morbidity and mortality in these patients. Optic pathways gliomas, plexiform neurofibromas and malignant peripheral nerve sheath tumor (MPNST) are the most frequent NF1-associated tumors. The treatment of these complications is often challenging, since surgery may not be feasible due to the location, size, and infiltrative nature of these tumors, and standard chemotherapy or radiotherapy are burdened by significant toxicity and risk for secondary malignancies. For these reasons, following the novel discoveries of the pathophysiological mechanisms that lead to cell proliferation and tumorigenesis in NF1 patients, emerging drugs targeting specific signalling pathways (i.e. the MEK/ERK cascade), have been developed with promising results.

Integrative Bayesian Analysis Identifies Rhabdomyosarcoma Disease Genes

Identifying oncogenic drivers and tumor suppressors remains a challenge in many forms of cancer, including rhabdomyosarcoma. Anticipating gene expression alterations resulting from DNA copy-number variants to be particularly important, we developed a computational and experimental strategy incorporating a Bayesian algorithm and CRISPR/Cas9 "mini-pool" screen that enables both genome-scale assessment of disease genes and functional validation. The algorithm, called iExCN, identified 29 rhabdomyosarcoma drivers and suppressors enriched for cell-cycle and nucleic-acid-binding activities. Functional studies showed that many iExCN genes represent rhabdomyosarcoma line-specific or shared vulnerabilities. Complementary experiments addressed modes of action and demonstrated coordinated repression of multiple iExCN genes during skeletal muscle differentiation. Analysis of two separate cohorts revealed that the number of iExCN genes harboring copy-number alterations correlates with survival. Our findings highlight rhabdomyosarcoma as a cancer in which multiple drivers influence disease biology and demonstrate a generalizable capacity for iExCN to unmask disease genes in cancer.

Molecular Characterization of a Rare Dedifferentiated Liposarcoma With Rhabdomyosarcomatous Differentiation in a 24 Year Old

Aims. The aim of this study was to identify potential driver genetic alterations in a dedifferentiated liposarcoma (DDLPS) with rhabdomyosarcomatous differentiation. Methods and Results. A 24-year-old female underwent resection of an abdominal mass, which on a previous biopsy demonstrated rhabdomyosarcomatous differentiation concerning for embryonal rhabdomyosarcoma. Histologically the resected tumor displayed a high-grade sarcoma with rhabdomyosarcomatous differentiation in the background of well-differentiated liposarcoma consistent with DDLPS. Fluorescence in situ hybridization confirmed MDM2 amplification, as did array-based copy number profiling. Whole-exome sequencing revealed a somatic FGFR1 hotspot mutation and RNA sequencing an LMNB2-MAP2K6 fusion only within the dedifferentiated component. Conclusions. This study represents an in-depth examination of a rare DDLPS with rhabdomyosarcomatous differentiation in a young individual. Additionally, it is also instructive of a potential pitfall when assessing for MDM2 amplification in small biopsies. Despite exhaustive analysis, mutation and gene copy number analysis did not identify any molecular events that would underlie the rhabdomyoblastic differentiation. Our understanding of what causes some tumors to dedifferentiate as well as undergo divergent differentiation is limited, and larger studies are needed.

MiRNAs as Players in Rhabdomyosarcoma Development

Rhabdomyosarcoma (RMS), the most common soft tissue sarcoma of childhood and adolescence, is a rare but aggressive malignancy that originates from immature mesenchymal cells committed to skeletal muscle differentiation. Although RMS is, generally, responsive to the modern multimodal therapeutic approaches, the prognosis of RMS depends on multiple variables and for some patients the outcome remains dismal. Further comprehension of the molecular and cellular biology of RMS would lead to identification of novel therapeutic targets. MicroRNAs (miRNAs) are small non-coding RNAs proved to function as key regulators of skeletal muscle cell fate determination and to play important roles in RMS pathogenesis. The purpose of this review is to better delineate the role of miRNAs as a biomarkers or functional leaders in RMS development, so to possibly elucidate some of RMS molecular mechanisms and potentially therapeutically target them to improve clinical management of pediatric RMS.

The current landscape of rhabdomyosarcomas: an update

Rhabdomyosarcomas are malignancies associated with a rhabdomyoblastic phenotype which can be demonstrated morphologically or by immunohistochemistry for MYOD1 and myogenin. Rhabdomyosarcomas are currently subdivided into 4 types in the 2013 WHO classification of tumors of soft tissue and bone, including embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, spindle cell/sclerosing rhabdomyosarcoma, and pleomorphic rhabdomyosarcoma. Recent studies have significantly impacted this classification with the emergence of three distinct new subtypes of rhabdomyosarcomas, namely rhabdomyosarcoma with MYOD1 mutations, rhabdomyosarcoma with TFCP2 fusions, and rhabdomyosarcoma with VGLL2/NCOA2 fusions. Although all these tumors share the terminology "rhabdomyosarcoma," their morphology, clinical behavior, and underlying molecular alterations are dramatically different. Finally, the presence of a rhabdomyoblastic phenotype within a tumor is by no means a diagnostic of a rhabdomyosarcoma, as this may be seen in many other mesenchymal malignancies, such as mesenchymal chondrosarcomas, malignant peripheral nerve sheaths tumors, and biphenotypic sinonasal sarcomas. In this review, we present the main clinical, morphological, and molecular features of these tumors and discuss the evolution of the current classification.

GEFT protein expression in digestive tract malignant tumors and its clinical significance

Guanine nucleotide exchange factor T (GEFT), a member of the Rho guanine nucleotide exchange factor family, is expressed in a variety of tumors. In the present study, the expression and clinical significance of GEFT in malignant digestive tract tumors was assessed. Tumor and adjacent control samples from 180 patients were tested. Positive GEFT expression rates were 80, 83.33 and 86.67% in esophageal squamous carcinoma (ESCC), gastric carcinoma (GC) and colorectal cancer (CRC), respectively. GEFT expression was associated with diffuse type carcinoma according to the Lauren classification (χ²=12.525, P=0.002) and tumor-node-metastasis (TNM) stages III/IV (χ²=4.033, P=0.045) in GC, and with vessel carcinoma embolus (χ²=7.890, P=0.005) and lymph node metastasis (χ²=5.455, P=0.020) in CRC, but was not associated with other clinicopathological parameters. Patients with high levels of GEFT protein expression had a less favorable outcome compared with patients with low levels of GEFT expression in patients with CRC (χ²=3.876, P=0.049). However, a significant association was not found between GEFT expression and overall survival in patients with ESCC (χ²=0.040, P=0.842) or GC (χ²=0.501, P=0.479). The rate of human epidermal growth factor receptor 2 upregulation in patients with GC was 13.33% and it was associated with nerve invasion (χ²=4.005, P=0.045) and TNM stages III/IV (χ²=5.600, P=0.018). Mismatch repair protein (MMRP) defect was observed in six cases, and the KRAS mutation rate was 26.67% in patients with CRC. GEFT expression was significantly correlated with MMRP (r=-0.285, P=0.027) and KRAS mutation in patients with CRC (r=0.697, P<0.001). These findings revealed frequent GEFT upregulation in malignant digestive tract tumors, which may have promoted tumor development. GEFT expression in CRC may be associated with microsatellite instability and KRAS mutation status, suggesting that GEFT may be a potential therapeutic target for patients with CRC.

Rhabdomyosarcoma arising from retroperitoneal teratoma in an infantile neurofibromatosis type 1 patient

We herein report the case of a 2-year-old girl with neurofibromatosis type 1 (NF1), who presented with a 12-cm mass in the right retroperitoneum and underwent tumor resection. Histologically, the tumor was composed of two distinct components: one was teratoma, showing mature morphology; and the other was embryonal rhabdomyosarcoma. An interphase fluorescence in situ hybridization (FISH) analysis of the rhabdomyosarcoma component revealed the absence of isochromosome 12p. Although it is well known that rhabdomyosarcoma occurs in infantile NF1, and that rhabdomyosarcoma can arise from teratoma as a somatic-type malignancy, to the best of our knowledge, this is the first case of an infantile NF1 patient, who developed rhabdomyosarcoma within a retroperitoneal teratoma. The absence of chromosome 12p alteration suggests a possibility that the rhabdomyosarcoma occurred due to the NF1 background, not as a somatic-type malignancy of germ cell tumor.

NF1 mutations identify molecular and clinical subtypes of lung adenocarcinomas

The tumor suppressor gene neurofibromin 1 (NF1) is a major regulator of the RAS-MAPK pathway. NF1 mutations occur in lung cancer but were not extensively explored. We hypothesized that NF1-mutated tumors could define a specific population with a distinct clinical and molecular profile. We performed NF1 sequencing using next generation sequencing (NGS) in 154 lung adenocarcinoma surgical specimens with known KRAS, EGFR, TP53, BRAF, HER2, and PIK3CA status, to evaluate the molecular and clinical specificities of NF1-mutated lung cancers. Clinical data were retrospectively collected, and their associations with molecular profiles assessed. In this series, 24 tumors were NF1 mutated (17.5%) and 11 were NF1 deleted (8%). There was no mutation hotspot. NF1 mutations were rarely associated with other RAS-MAPK pathway mutations. Most of patients with NF1 alterations were males (74.3%) and smokers (74.3%). Overall survival and disease-free survival were statistically better in patients with NF1 alterations (N = 34) than in patients with KRAS mutations (N = 30) in univariate analysis. Our results confirm that NF1 is frequently mutated and represents a distinct molecular and clinical subtype of lung adenocarcinoma.

Histiocyte-rich rhabdomyoblastic tumor: rhabdomyosarcoma, rhabdomyoma, or rhabdomyoblastic tumor of uncertain malignant potential? A histologically distinctive rhabdomyoblastic tumor in search of a place in the classification of skeletal muscle neoplasms

Skeletal muscle tumors are traditionally classified as rhabdomyoma or rhabdomyosarcoma. We have identified an unusual adult rhabdomyoblastic tumor not clearly corresponding to a previously described variant of rhabdomyoma or rhabdomyosarcoma, characterized by a very striking proliferation of non-neoplastic histiocytes, obscuring the underlying tumor. Ten cases were identified in nine males and one female with a median age of 43 years (range 23-69 years). Tumors involved the deep soft tissues of the trunk (N = 4), lower limbs (N = 4), and neck (N = 2). Tumors were well-circumscribed, nodular masses, frequently surrounded by a fibrous capsule containing lymphoid aggregates and sometimes calcifications. Numerous foamy macrophages, multinucleated Touton-type giant cells, and sheets/fascicles of smaller, often spindled macrophages largely obscured the underlying desmin, MyoD1, and myogenin-positive rhabdomyoblastic tumor. Cases were wild type for MYOD1 and no other mutations or rearrangements characteristic of a known subtype of rhabdomyoma or rhabdomyosarcoma were identified. Two of four cases successfully analyzed using a next-generation sequencing panel of 170 common cancer-related genes harbored inactivating NF1 mutations. Next-generation sequencing showed no gene fusions. Clinical follow (nine patients; median 9 months; mean 23 months; range 3-124 months) showed all patients received wide excision; four patients also received adjuvant radiotherapy and none received chemotherapy. At the time of last follow-up, all patients were alive and without disease; no local recurrences or distant metastases occurred. We hypothesize that these unusual tumors represent rhabdomyoblastic tumors of uncertain malignant potential. Possibly over time they should be relegated to a new category of skeletal muscle tumors of intermediate (borderline) malignancy.

Update on Myogenic Sarcomas

Myogenic sarcomas include soft tissue sarcomas that show skeletal muscle differentiation (rhabdomyosarcoma) and those with smooth muscle differentiation (leiomyosarcoma). Rhabdomyosarcomas are more common in the pediatric age group and leiomyosarcomas occur more often in the adult population. Based on the clinico-pathologic features and genetic abnormalities identified, the rhabdomyosarcomas are classified into embryonal, alveolar, spindle cell/sclerosing, and pleomorphic subtypes. Each subtype shows distinctive morphology and has characteristic genetic abnormalities. In this update on myogenic sarcomas, each entity is discussed with special emphasis on recent updates in genetic findings and the diagnostic approach to these tumors.

A review of soft-tissue sarcomas: translation of biological advances into treatment measures

Soft-tissue sarcomas are rare malignant tumors arising from connective tissues and have an overall incidence of about five per 100,000 per year. While this diverse family of malignancies comprises over 100 histological subtypes and many molecular aberrations are prevalent within specific sarcomas, very few are therapeutically targeted. Instead of utilizing molecular signatures, first-line sarcoma treatment options are still limited to traditional surgery and chemotherapy, and many of the latter remain largely ineffective and are plagued by disease resistance. Currently, the mechanism of sarcoma oncogenesis remains largely unknown, thus necessitating a better understanding of pathogenesis. Although substantial progress has not occurred with molecularly targeted therapies over the past 30 years, increased knowledge about sarcoma biology could lead to new and more effective treatment strategies to move the field forward. Here, we discuss biological advances in the core molecular determinants in some of the most common soft-tissue sarcomas - liposarcoma, angiosarcoma, leiomyosarcoma, rhabdomyosarcoma, Ewing's sarcoma, and synovial sarcoma - with an emphasis on emerging genomic and molecular pathway targets and immunotherapeutic treatment strategies to combat this confounding disease.

Functional screening of FGFR4-driven tumorigenesis identifies PI3K/mTOR inhibition as a therapeutic strategy in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma and outcomes have stagnated, highlighting a need for novel therapies. Genomic analysis of RMS has revealed that alterations in the receptor tyrosine kinase (RTK)/RAS/PI3K axis are common and that FGFR4 is frequently mutated or overexpressed. Although FGFR4 is a potentially druggable receptor tyrosine kinase, its functions in RMS are undefined. This study tested FGFR4-activating mutations and overexpression for the ability to generate RMS in mice. Murine tumor models were subsequently used to discover potential therapeutic targets and to test a dual PI3K/mTOR inhibitor in a preclinical setting. Specifically, we provide the first mechanistic evidence of differential potency in the most common human RMS mutations, V550E or N535K, compared to FGFR4^wt overexpression as murine myoblasts expressing FGFR4^V550E undergo higher rates of cellular transformation, engraftment into mice, and rapidly form sarcomas that highly resemble human RMS. Murine tumor cells overexpressing FGFR4^V550E were tested in an in vitro dose-response drug screen along with human RMS cell lines. Compounds were grouped by target class, and potency was determined using average percentage of area under the dose-response curve (AUC). RMS cells were highly sensitive to PI3K/mTOR inhibitors, in particular, GSK2126458 (omipalisib) was a potent inhibitor of FGFR4^V550E tumor-derived cell and human RMS cell viability. FGFR4^V550E-overexpressing myoblasts and tumor cells had low nanomolar GSK2126458 EC₅₀ values. Mass cytometry using mouse and human RMS cell lines validated GSK2126458 specificity at single-cell resolution, decreasing the abundance of phosphorylated Akt as well as decreasing phosphorylation of the downstream mTOR effectors 4ebp1, Eif4e, and S6. Moreover, PI3K/mTOR inhibition also robustly decreased the growth of RMS tumors in vivo. Thus, by developing a preclinical platform for testing novel therapies, we identified PI3K/mTOR inhibition as a promising new therapy for this devastating pediatric cancer.

Functional screening of FGFR4-driven tumorigenesis identifies PI3K/mTOR inhibition as a therapeutic strategy in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma and outcomes have stagnated, highlighting a need for novel therapies. Genomic analysis of RMS has revealed that alterations in the receptor tyrosine kinase (RTK)/RAS/PI3K axis are common and that FGFR4 is frequently mutated or overexpressed. Although FGFR4 is a potentially druggable receptor tyrosine kinase, its functions in RMS are undefined. This study tested FGFR4-activating mutations and overexpression for the ability to generate RMS in mice. Murine tumor models were subsequently used to discover potential therapeutic targets and to test a dual PI3K/mTOR inhibitor in a preclinical setting. Specifically, we provide the first mechanistic evidence of differential potency in the most common human RMS mutations, V550E or N535K, compared to FGFR4^wt overexpression as murine myoblasts expressing FGFR4^V550E undergo higher rates of cellular transformation, engraftment into mice, and rapidly form sarcomas that highly resemble human RMS. Murine tumor cells overexpressing FGFR4^V550E were tested in an in vitro dose-response drug screen along with human RMS cell lines. Compounds were grouped by target class, and potency was determined using average percentage of area under the dose-response curve (AUC). RMS cells were highly sensitive to PI3K/mTOR inhibitors, in particular, GSK2126458 (omipalisib) was a potent inhibitor of FGFR4^V550E tumor-derived cell and human RMS cell viability. FGFR4^V550E-overexpressing myoblasts and tumor cells had low nanomolar GSK2126458 EC₅₀ values. Mass cytometry using mouse and human RMS cell lines validated GSK2126458 specificity at single-cell resolution, decreasing the abundance of phosphorylated Akt as well as decreasing phosphorylation of the downstream mTOR effectors 4ebp1, Eif4e, and S6. Moreover, PI3K/mTOR inhibition also robustly decreased the growth of RMS tumors in vivo. Thus, by developing a preclinical platform for testing novel therapies, we identified PI3K/mTOR inhibition as a promising new therapy for this devastating pediatric cancer.

Hedgehog Pathway Drives Fusion-Negative Rhabdomyosarcoma Initiated From Non-myogenic Endothelial Progenitors

Rhabdomyosarcoma (RMS) is a pediatric soft tissue sarcoma that histologically resembles embryonic skeletal muscle. RMS occurs throughout the body and an exclusively myogenic origin does not account for RMS occurring in sites devoid of skeletal muscle. We previously described an RMS model activating a conditional constitutively active Smoothened mutant (SmoM2) with aP2-Cre. Using genetic fate mapping, we show SmoM2 expression in Cre-expressing endothelial progenitors results in myogenic transdifferentiation and RMS. We show that endothelium and skeletal muscle within the head and neck arise from Kdr-expressing progenitors, and that hedgehog pathway activation results in aberrant expression of myogenic specification factors as a potential mechanism driving RMS genesis. These findings suggest that RMS can originate from aberrant development of non-myogenic cells.

Multiplexed in vivo homology-directed repair and tumor barcoding enables parallel quantification of Kras variant oncogenicity

Large-scale genomic analyses of human cancers have cataloged somatic point mutations thought to initiate tumor development and sustain cancer growth. However, determining the functional significance of specific alterations remains a major bottleneck in our understanding of the genetic determinants of cancer. Here, we present a platform that integrates multiplexed AAV/Cas9-mediated homology-directed repair (HDR) with DNA barcoding and high-throughput sequencing to simultaneously investigate multiple genomic alterations in de novo cancers in mice. Using this approach, we introduce a barcoded library of non-synonymous mutations into hotspot codons 12 and 13 of Kras in adult somatic cells to initiate tumors in the lung, pancreas, and muscle. High-throughput sequencing of barcoded Kras HDR alleles from bulk lung and pancreas reveals surprising diversity in Kras variant oncogenicity. Rapid, cost-effective, and quantitative approaches to simultaneously investigate the function of precise genomic alterations in vivo will help uncover novel biological and clinically actionable insights into carcinogenesis.

A Novel Notch-YAP Circuit Drives Stemness and Tumorigenesis in Embryonal Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), a cancer characterized by skeletal muscle features, is the most common soft-tissue sarcoma of childhood. While low- and intermediate-risk groups have seen improved outcomes, high-risk patients still face a 5-year survival rate of <30%, a statistic that has not changed in over 40 years. Understanding the biologic underpinnings of RMS is critical. The developmental pathways of Notch and YAP have been identified as potent but independent oncogenic signals that support the embryonal variant of RMS (eRMS). Here, the cross-talk between these pathways and the impact on eRMS tumorigenesis is reported. Using human eRMS cells grown as three-dimensional (3D) rhabdospheres, which enriches in stem cells, it was found that Notch signaling transcriptionally upregulates YAP1 gene expression and YAP activity. Reciprocally, YAP transcriptionally upregulates the Notch ligand genes JAG1 and DLL1 and the core Notch transcription factor RBPJ This bidirectional circuit boosts expression of key stem cell genes, including SOX2, which is functionally required for eRMS spheres. Silencing this circuit for therapeutic purposes may be challenging, because the inhibition of one node (e.g., pharmacologic Notch blockade) can be rescued by upregulation of another (constitutive YAP expression). Instead, dual inhibition of Notch and YAP is necessary. Finally, supporting the existence of this circuit beyond a model system, nuclear Notch and YAP protein expression are correlated in human eRMS tumors, and YAP suppression in vivo decreases Notch signaling and SOX2 expression.Implications: This study identifies a novel oncogenic signaling circuit driving eRMS stemness and tumorigenesis, and provides evidence and rationale for combination therapies co-targeting Notch and YAP. Mol Cancer Res; 15(12); 1777-91. ©2017 AACR.

Congenital Eyelid Rhabdomyosarcoma

Rhabdomyosarcoma is the most common type of soft tissue sarcoma in children. The authors present a rare case of eyelid rhabdomyosarcoma in a newborn, who was found to have a reddish eyelid tumor in his OD. A mass with a clear margin, confined to the upper eyelid, was revealed using orbital MRI. Intralesional steroids were injected under the impression of a capillary hemangioma and the tumor shrank initially, but grew rapidly later. Therefore, a debulking surgery was performed and the final diagnosis was embryonal rhabdomyosarcoma. After the operation, metastases still occurred despite the treatment with chemotherapy and concurrent radiation. The patient expired at 6 months of age. In an autopsy, a neuroblastoma was incidentally found in his left adrenal gland. Early biopsy may help lead to an early correct diagnosis and avoid metastases in similar cases.

Distinctive Head and Neck Bone and Soft Tissue Neoplasms

Benign and malignant primary bone and soft tissue lesions of the head and neck are rare. The uncommon nature of these tumors, combined with the complex anatomy of the head and neck, pose diagnostic challenges to pathologists. This article describes the pertinent clinical, radiographic, and pathologic features of selected bone and soft tissue tumors involving the head and neck region, including angiofibroma, glomangiopericytoma, rhabdomyosarcoma, biphenotypic sinonasal sarcoma, chordoma, chondrosarcoma, and osteosarcoma. Emphasis is placed on key diagnostic pitfalls, differential diagnosis, and the importance of correlating clinical and radiographic information, particularly for tumors involving bone.

Update on molecular findings in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common malignant soft tissue tumour in children and adolescents. Histologically RMS resembles developing fetal striated skeletal muscle. RMS is stratified into different histological subtypes which appear to influence management plans and patient outcome. Importantly, molecular classification of RMS seems to more accurately capture the true biology and clinical course and prognosis of RMS to guide therapeutic decisions. The identification of PAX-FOXO1 fusion status in RMS is one of the most important updates in the risk stratification of RMS. There are several genes close to PAX that are frequently altered including the RAS family, FGFR4, PIK3CA, CTNNB1, FBXW7, and BCOR. As with most paediatric blue round cell tumours and sarcomas, chemotherapy is the key regimen for RMS therapy. Currently there are no direct inhibitors against PAX-FOXO1 fusion oncoproteins and targeting epigenetic cofactors is limited to clinical trials. Failure of therapy in RMS is usually related to drug resistance and metastatic disease. Through this review we have highlighted most of the molecular aspects in RMS and have attempted to correlate with RMS classification, treatment and prognosis.

Use of liquid biopsies to monitor disease progression in a sarcoma patient: a case report

BACKGROUND

Many patients experience local recurrence or metastases after receiving potentially curative treatment, and early detection of these events is important for disease control. Recent technological advances make it possible to use blood plasma containing circulating cell-free tumour DNA (ctDNA) as a liquid biopsy. In this case report we show how serial liquid biopsies can be used to monitor the disease course and detect disease recurrence in a sarcoma patient.

CASE PRESENTATION

A 55-year-old male presented with a rapidly growing, painful palpable mass in the left groin region, and a biopsy revealed a high-grade malignant spindle cell sarcoma. No metastases were detected on radiologic imaging scans. Using targeted resequencing with a custom 900 cancer gene panel, eight somatic mutations among them KRAS and NF1, were identified in the primary tumour. Targeted resequencing of plasma cell-free DNA (ctDNA) collected before and after surgery and at disease progression confirmed the presence of six of eight mutations at all three time points. The ctDNA level, estimated from the somatic allele frequencies of these six mutations, was high in plasma taken at the time of surgery, at levels similar to the primary tumour. Detection of low levels of ctDNA three days after surgery indicated persistent microscopic disease. Repeated radiologic imaging six weeks postoperatively showed widespread metastatic disease in the lungs, skeleton and the pelvic region. At this time point there was a dramatic increase in the ctDNA level, reflecting the disease progression of the patient. The patient had an unusually aggressive cancer, and succumbed to the disease 13 weeks after surgery.

CONCLUSIONS

This case report demonstrated that targeted resequencing of ctDNA from longitudinal collected plasma can be used to monitor disease progression in a soft tissue sarcoma patient, including manifestation of metastatic disease. The ctDNA represented the genomic profile of the tumour, supporting clinical use of liquid biopsies to identify tumour-specific mutations as well as recurrent disease.

Discovering novel oncogenic pathways and new therapies using zebrafish models of sarcoma

Sarcoma is a type of cancer affecting connective, supportive, or soft tissue of mesenchymal origin. Despite rare incidence in adults (<1%), over 15% of pediatric cancers are sarcoma. Sadly, both adults and children with relapsed or metastatic disease have devastatingly high rates of mortality. Current treatment options for sarcoma include surgery, radiation, and/or chemotherapy; however, significant limitations exist with respect to the efficacy of these strategies. Strong impetus has been placed on the development of novel therapies and preclinical models for uncovering mechanisms involved in the development, progression, and therapy resistance of sarcoma. Over the past 15 years, the zebrafish has emerged as a powerful genetic model of human cancer. High genetic conservation when combined with a unique susceptibility to develop sarcoma has made the zebrafish an effective tool for studying these diseases. Transgenic and gene-activation strategies have been employed to develop zebrafish models of rhabdomyosarcoma, malignant peripheral nerve sheath tumors, Ewing's sarcoma, chordoma, hemangiosarcoma, and liposarcoma. These models all display remarkable molecular and histopathological conservation with their human cancer counterparts and have offered excellent platforms for understanding disease progression in vivo. Short tumor latency and the amenability of zebrafish for ex vivo manipulation, live imaging studies, and tumor cell transplantation have allowed for efficient study of sarcoma initiation, growth, self-renewal, and maintenance. When coupled with facile chemical genetic approaches, zebrafish models of sarcoma have provided a strong translational tool to uncover novel drug pathways and new therapeutic strategies.

Hedgehog Pathway in Pediatric Cancers: They're Not Just for Brain Tumors Anymore

The Hedgehog (HH) pathway regulates fundamental processes in embryonic development, including stem cell maintenance, cell differentiation, tissue polarity, and cell proliferation. In the vertebrate pathway, Sonic hedgehog (SHH) binds to Patched1 (PTCH1), which relieves its inhibition of Smoothened (SMO), allowing the GLI family of transcription factors to translocate to the nucleus and activate HH target genes such as GLI1, GLI2, PTCH1, CYCLIN D1, BCL-2, and MYCN. The HH pathway is also an active participant in tumorigenesis. In 1996, loss-of-function mutation in PTCH1 was discovered to be the cause of nevoid basal cell carcinoma syndrome (NBCCS, or Gorlin syndrome), an autosomal dominant disease associated with increased rates of basal cell carcinoma (BCC), medulloblastoma (MB), and rarely, rhabdomyosarcoma. It is now estimated that 100% of sporadic BCC and up to 20% to 30% of MB also harbor activating HH pathway mutations. Together, these discoveries firmly established the linkage between HH pathway activation and cancer development. Intense research has since been focused on further defining the role of the HH pathway in BCC and MB and potential therapeutic strategies to inhibit HH signaling. Early clinical trials of SMO inhibitors have shown promising results in the treatment of adult BCC and SHH-driven MB. More recently, a number of other pediatric cancers have been reported to show HH activity, making these tumors potential candidates for HH inhibitor therapy. To date however, no HH pathway mutations have been identified in other pediatric cancers. This review will describe the HH pathway signaling in development and cancer with a focus on recent evidence for HH pathway activation in central nervous system (CNS) and non-CNS pediatric cancers.

Hepatocyte Growth Factor-mediated satellite cells niche perturbation promotes development of distinct sarcoma subtypes

Embryonal Rhabdomyosarcoma (ERMS) and Undifferentiated Pleomorphic Sarcoma (UPS) are distinct sarcoma subtypes. Here we investigate the relevance of the satellite cell (SC) niche in sarcoma development by using Hepatocyte Growth Factor (HGF) to perturb the niche microenvironment. In a Pax7 wild type background, HGF stimulation mainly causes ERMS that originate from satellite cells following a process of multistep progression. Conversely, in a Pax7 null genotype ERMS incidence drops, while UPS becomes the most frequent subtype. Murine EfRMS display genetic heterogeneity similar to their human counterpart. Altogether, our data demonstrate that selective perturbation of the SC niche results in distinct sarcoma subtypes in a Pax7 lineage-dependent manner, and define a critical role for the Met axis in sarcoma initiation. Finally, our results provide a rationale for the use of combination therapy, tailored on specific amplifications and activated signaling pathways, to minimize resistance emerging from sarcomas heterogeneity.

DOI:http://dx.doi.org/10.7554/eLife.12116.001

Soft tissue sarcomas are rare cancers that originate in tissues such as muscles, tendons, cartilage and fat. These cancers are further classified into subtypes based on their appearance. For example, rhabdomyosarcoma cells resemble the cells that normally develop into muscle, while other soft tissue tumors that do not look like a distinct cell type are called undifferentiated pleomorphic sarcomas. Recent experiments have suggested that although these subtypes appear different, they may both arise from the cells that build muscles. However, this had not been confirmed.

Morena et al. investigated whether changing the environment – also known as the “niche” – of muscle stem cells could influence what type of sarcoma developed in mice that were prone to cancer. Normally muscle stem cells in an adult only regenerate injured muscles, and need to receive the correct cues before they divide. Among these cues is a protein called Hepatocyte Growth Factor (or HGF for short), which is produced by cells in the muscle stem cells’ niche.

Morena et al. engineered mice so that the production of HGF in the muscles could be switched on or off at will. Mice that were already prone to cancer and produced a lot of HGF tended to develop rhabdomyosarcomas. However, when HGF was turned on in similar mice that also lacked normal muscle stem cells, the resulting sarcomas were predominantly undifferentiated pleomorphic sarcomas. These data indicate that rhabdomyosarcomas probably originate from muscle stem cells, whereas undifferentiated pleomorphic sarcomas develop from other cells in the niche.

Lastly, Morena et al. studied the sarcomas in their mice in more detail and observed that, similar to what has been found in human rhabdomyosarcomas, individual tumors had different genetic mutations. These differences make it difficult to treat sarcomas with a single anti-cancer drug. However, the new results suggest that a combination of targeted drugs may prove effective in blocking tumor growth and in preventing resistance.

DOI:http://dx.doi.org/10.7554/eLife.12116.002

A Polymorphism in the FGFR4 Gene Is Associated With Risk of Neuroblastoma and Altered Receptor Degradation

BACKGROUND

Outcomes for children with high-risk neuroblastoma are poor, and improved understanding of the mechanisms underlying neuroblastoma pathogenesis, recurrence, and treatment resistance will lead to improved outcomes. Aberrant growth factor receptor expression and receptor tyrosine kinase signaling are associated with the pathogenesis of many malignancies. A germline polymorphism in the FGFR4 gene is associated with increased receptor expression and activity and with decreased survival, treatment resistance, and aggressive disease for many malignancies. We therefore investigated the role of this FGFR4 polymorphism in neuroblastoma pathogenesis.

MATERIALS AND METHODS

Germline DNA from neuroblastoma patients and matched controls was assessed for the FGFR4 Gly/Arg388 polymorphism by RT-PCR. Allele frequencies were assessed for association with neuroblastoma patient outcomes and prognostic features. Degradation rates of the FGFR4 Arg388 and Gly388 receptors and rates of receptor internalization into the late endosomal compartment were measured.

RESULTS

Frequency of the FGFR4 AA genotype and the prevalence of the A allele were significantly higher in patients with neuroblastoma than in matched controls. The Arg388 receptor demonstrated slower degradation than the Gly388 receptor in neuroblastoma cells and reduced internalization into multivesicular bodies.

CONCLUSIONS

The FGFR4 Arg388 polymorphism is associated with an increased prevalence of neuroblastoma in children, and this association may be linked to differences in FGFR4 degradation rates. Our study provides the first evidence of a role for FGFR4 in neuroblastoma, suggesting that FGFR4 genotype and the pathways regulating FGFR4 trafficking and degradation may be relevant for neuroblastoma pathogenesis.

Identification of a novel synthetic lethality of combined inhibition of hedgehog and PI3K signaling in rhabdomyosarcoma

We previously reported that aberrant HH pathway activation confers a poor prognosis in rhabdomyosarcoma (RMS). Searching for new treatment strategies we therefore targeted HH signaling. Here, we identify a novel synthetic lethality of concomitant inhibition of HH and PI3K/AKT/mTOR pathways in RMS by GLI1/2 inhibitor GANT61 and PI3K/mTOR inhibitor PI103. Synergistic drug interaction is confirmed by calculation of combination index (CI < 0.2). Similarly, genetic silencing of GLI1/2 significantly increases PI103-induced apoptosis. GANT61 and PI103 also synergize to induce apoptosis in cultured primary RMS cells emphasizing the clinical relevance of this combination. Importantly, GANT61/PI103 cotreatment suppresses clonogenic survival, three-dimensional sphere formation and tumor growth in an in vivo model of RMS. Mechanistic studies reveal that GANT61 and PI103 cooperate to trigger caspase-dependent apoptosis via the mitochondrial pathway, as demonstrated by several lines of evidence. First, GANT61/PI103 cotreatment increases mRNA and protein expression of NOXA and BMF, which is required for apoptosis, since knockdown of NOXA or BMF significantly reduces GANT61/PI103-induced apoptosis. Second, GANT61/PI103 cotreatment triggers BAK/BAX activation, which contributes to GANT61/PI103-mediated apoptosis, since knockdown of BAK provides protection. Third, ectopic expression of BCL-2 or non-degradable phospho-mutant MCL-1 significantly rescue GANT61/PI103-triggered apoptosis. Fourth, GANT61/PI103 cotreatment initiate activation of the caspase cascade via apoptosome-mediated cleavage of the initiator caspase-9, as indicated by changes in the cleavage pattern of caspases (e.g. accumulation of the caspase-9 p35 cleavage fragment) upon addition of the caspase inhibitor zVAD.fmk. Thus, combined GLI1/2 and PI3K/mTOR inhibition represents a promising novel approach for synergistic apoptosis induction and tumor growth reduction with implications for new treatment strategies in RMS.

Emerging molecular-targeted therapies in early-phase clinical trials and preclinical models

Within the context of modern cooperative group trials, modification of standard cytotoxic chemotherapy has not improved survival in patients with rhabdomyosarcoma (RMS) over the last 30 years. There is need and interest to incorporate novel targeted anticancer agents into the treatment plans for children and adolescents with newly diagnosed RMS; however, targets directly driven by FOXO1 translocation remain elusive, and molecular events driving translocation negative tumors similarly remain ill-defined. Thus, alternate pathways driving the tumors require identification and targeting. Herein, we describe targeted therapies that could be of interest in RMS, but whose inclusion in clinical trials is thus far limited by scientific and regulatory criteria. Sorafenib, pazopanib, crizotinib, TH-302, aurora-kinase inhibitors, and anaplastic lymphoma kinase (ALK)/c-MET inhibitors will be discussed. The current preclinical and clinical data available, as well as limitations and challenges for each, will be outlined.

Histone Deacetylase Inhibitors Antagonize Distinct Pathways to Suppress Tumorigenesis of Embryonal Rhabdomyosarcoma

Embryonal rhabdomyosarcoma (ERMS) is the most common soft tissue cancer in children. The prognosis of patients with relapsed or metastatic disease remains poor. ERMS genomes show few recurrent mutations, suggesting that other molecular mechanisms such as epigenetic regulation might play a major role in driving ERMS tumor biology. In this study, we have demonstrated the diverse roles of histone deacetylases (HDACs) in the pathogenesis of ERMS by characterizing effects of HDAC inhibitors, trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA; also known as vorinostat) in vitro and in vivo. TSA and SAHA suppress ERMS tumor growth and progression by inducing myogenic differentiation as well as reducing the self-renewal and migratory capacity of ERMS cells. Differential expression profiling and pathway analysis revealed downregulation of key oncogenic pathways upon HDAC inhibitor treatment. By gain-of-function, loss-of-function, and chromatin immunoprecipitation (ChIP) studies, we show that Notch1- and EphrinB1-mediated pathways are regulated by HDACs to inhibit differentiation and enhance migratory capacity of ERMS cells, respectively. Our study demonstrates that aberrant HDAC activity plays a major role in ERMS pathogenesis. Druggable targets in the molecular pathways affected by HDAC inhibitors represent novel therapeutic options for ERMS patients.

The NF1 gene revisited - from bench to bedside

Neurofibromatosis type 1 (NF1) is a relatively common tumour predisposition syndrome related to germline aberrations of NF1, a tumour suppressor gene. The gene product neurofibromin is a negative regulator of the Ras cellular proliferation pathway, and also exerts tumour suppression via other mechanisms.

Recent next-generation sequencing projects have revealed somatic NF1 aberrations in various sporadic tumours. NF1 plays a critical role in a wide range of tumours. NF1 alterations appear to be associated with resistance to therapy and adverse outcomes in several tumour types.

Identification of a patient's germline or somatic NF1 aberrations can be challenging, as NF1 is one of the largest human genes, with a myriad of possible mutations. Epigenetic factors may also contribute to inadequate levels of neurofibromin in cancer cells.

Clinical trials of NF1-based therapeutic approaches are currently limited. Preclinical studies on neurofibromin-deficient malignancies have mainly been on malignant peripheral nerve sheath tumour cell lines or xenografts derived from NF1 patients. However, the emerging recognition of the role of NF1 in sporadic cancers may lead to the development of NF1-based treatments for other tumour types. Improved understanding of the implications of NF1 aberrations is critical for the development of novel therapeutic strategies.