Histology, Fusion Status, and Outcome in Alveolar Rhabdomyosarcoma With Low-Risk Clinical Features: A Report From the Children's Oncology Group

Significance of fusion status, Oberlin risk factors, local and maintenance treatment in pediatric and adolescent patients with metastatic rhabdomyosarcoma: Data of the European Soft Tissue Sarcoma Registry SoTiSaR

BACKGROUND

Outcome of primary metastatic rhabdomyosarcoma (RMS) is poor. Certain risk factors as fusion status, Oberlin score, and local treatment of primary tumor are known to influence prognosis.

PROCEDURE

Patients with metastatic RMS were treated according to Cooperative Weichteilsarkom Studiengruppe (CWS) guidance with chemotherapy (CHT), radiotherapy (RT) excluding total lung irradiation (TLI), complete resection of the primary tumor, and metastasectomy if possible. Kaplan-Meier estimators and Cox proportional hazard models were used to examine event-free survival (EFS) and overall survival (OS) involving also landmark analyses.

RESULTS

In the European Soft Tissue Sarcoma Registry SoTiSaR (2009-2018), 211 patients were analyzed. Many patients had fusion-positive alveolar RMS (n = 83; 39%). Median age was 9.4 years [0.1-19.7 years]. Treatment primarily consisted of CHT with CEVAIE (carboplatin, epirubicine, vincristine, actinomycin-D, ifosfamide, etoposide: 86%, other regimens: 14%), RT (71%), resection of primary tumor (37%), metastasectomy (19%), and lymph node sampling/dissection (21%). Maintenance treatment (MT) (oral trofosfamide, idarubicin, etoposide) was added in 74% of patients. Oberlin factors, fusion status, and MT were predictive for EFS and OS. MT with O-TIE was not improving outcome when adjusting for the immortal time bias. Local treatment of the primary tumor and radical irradiation (except TLI) improved EFS, not OS, when adjusting for the Oberlin score. Patients with fusion-negative alveolar RMS (n = 9) had an excellent outcome with a 5-year EFS and OS of 100%, compared to patients with embryonal RMS (49%/62%), PAX7- (22%/47%) and PAX3/FOXO1-positive ARMS (10/13%), respectively (p < .001).

CONCLUSIONS

Prognosis of metastatic RMS primarily depends on fusion status and Oberlin score. Fusion status needs to be considered in future trials to optimize treatment outcome. The role of radical irradiation needs further investigation.

Genomic and Epigenetic Changes Drive Aberrant Skeletal Muscle Differentiation in Rhabdomyosarcoma

Rhabdomyosarcoma (RMS), the most common soft-tissue sarcoma in children and adolescents, represents an aberrant form of skeletal muscle differentiation. Both skeletal muscle development, as well as regeneration of adult skeletal muscle are governed by members of the myogenic family of regulatory transcription factors (MRFs), which are deployed in a highly controlled, multi-step, bidirectional process. Many aspects of this complex process are deregulated in RMS and contribute to tumorigenesis. Interconnected loops of super-enhancers, called core regulatory circuitries (CRCs), define aberrant muscle differentiation in RMS cells. The transcriptional regulation of MRF expression/activity takes a central role in the CRCs active in skeletal muscle and RMS. In PAX3::FOXO1 fusion-positive (PF+) RMS, CRCs maintain expression of the disease-driving fusion oncogene. Recent single-cell studies have revealed hierarchically organized subsets of cells within the RMS cell pool, which recapitulate developmental myogenesis and appear to drive malignancy. There is a large interest in exploiting the causes of aberrant muscle development in RMS to allow for terminal differentiation as a therapeutic strategy, for example, by interrupting MEK/ERK signaling or by interfering with the epigenetic machinery controlling CRCs. In this review, we provide an overview of the genetic and epigenetic framework of abnormal muscle differentiation in RMS, as it provides insights into fundamental mechanisms of RMS malignancy, its remarkable phenotypic diversity and, ultimately, opportunities for therapeutic intervention.

Exosome-Based Liquid Biopsy Approaches in Bone and Soft Tissue Sarcomas: Review of the Literature, Prospectives, and Hopes for Clinical Application

The knowledge of exosome impact on sarcoma development and progression has been implemented in preclinical studies thanks to technological advances in exosome isolation. Moreover, the clinical relevance of liquid biopsy is well established in early diagnosis, prognosis prediction, tumor burden assessment, therapeutic responsiveness, and recurrence monitoring of tumors. In this review, we aimed to comprehensively summarize the existing literature pointing out the clinical relevance of detecting exosomes in liquid biopsy from sarcoma patients. Presently, the clinical utility of liquid biopsy based on exosomes in patients affected by sarcoma is under debate. The present manuscript collects evidence on the clinical impact of exosome detection in circulation of sarcoma patients. The majority of these data are not conclusive and the relevance of liquid biopsy-based approaches in some types of sarcoma is still insufficient. Nevertheless, the utility of circulating exosomes in precision medicine clearly emerged and further validation in larger and homogeneous cohorts of sarcoma patients is clearly needed, requiring collaborative projects between clinicians and translational researchers for these rare cancers.

Cutaneous Metastasis of Alveolar Rhabdomyosarcoma in a Child

ABSTRACT

Rhabdomyosarcoma (RMS) is one of the most common soft tissue sarcomas in children. This lesion is classically included in the generic group of "small round blue cell tumors" along with other entities that share similar microscopic features. Although the head and neck region is a frequent site for primary tumors, cutaneous metastases of RMS involving this anatomical location are rare in the pediatric population. We report a case of a 12-year old girl previously diagnosed with a primary alveolar RMS involving the left maxillary sinus, presenting with a metastatic lesion on the skin of the left temple area. Along with a brief review of the previous case reports on the topic, we highlight the initial immunohistochemistry panel useful for diagnosing this tumor.

Molecular testing of rhabdomyosarcoma in clinical trials to improve risk stratification and outcome: A consensus view from European paediatric Soft tissue sarcoma Study Group, Children's Oncology Group and Cooperative Weichteilsarkom-Studiengruppe

Rhabdomyosarcomas (RMSs) are the most common soft tissue sarcomas in children/adolescents less than 18 years of age with an annual incidence of 1-2/million. Inter/intra-tumour heterogeneity raise challenges in clinical, pathological and biological research studies. Risk stratification in European and North American clinical trials previously relied on clinico-pathological features, but now, incorporates PAX3/7-FOXO1-fusion gene status in the place of alveolar histology. International working groups propose a coordinated approach through the INternational Soft Tissue SaRcoma ConsorTium to evaluate the specific genetic abnormalities and generate and integrate molecular and clinical data related to patients with RMS across different trial settings. We review relevant data and present a consensus view on what molecular features should be assessed. In particular, we recommend the assessment of the MYOD1-LR122R mutation for risk escalation, as it has been associated with poor outcomes in spindle/sclerosing RMS and rare RMS with classic embryonal histopathology. The prospective analyses of rare fusion genes beyond PAX3/7-FOXO1 will generate new data linked to outcomes and assessment of TP53 mutations and CDK4 amplification may confirm their prognostic value. Pathogenic/likely pathogenic germline variants in TP53 and other cancer predisposition genes should also be assessed. DNA/RNA profiling of tumours at diagnosis/relapse and serial analyses of plasma samples is recommended where possible to validate potential molecular biomarkers, identify new biomarkers and assess how liquid biopsy analyses can have the greatest benefit. Together with the development of new molecularly-derived therapeutic strategies that we review, a synchronised international approach is expected to enhance progress towards improved treatment assignment, management and outcomes for patients with RMS.

An update on rhabdomyosarcoma risk stratification and the rationale for current and future Children's Oncology Group clinical trials

Children and adolescents with rhabdomyosarcoma (RMS) comprise a heterogeneous population with variable overall survival rates ranging between approximately 6% and 100% depending on defined risk factors. Although the risk stratification of patients has been refined across five decades of collaborative group studies, molecular prognostic biomarkers beyond FOXO1 fusion status have yet to be incorporated prospectively in upfront risk-based therapy assignments. This review describes the evolution of risk-based therapy and the current risk stratification, defines a new risk stratification incorporating novel biomarkers, and provides the rationale for the current and upcoming Children's Oncology Group RMS studies.

An Integrative Morphologic and Molecular Approach for Diagnosis of Rhabdomyosarcoma and Subclassification of Rhabdomyosarcoma

CONTEXT.—

Rhabdomyosarcoma, the most common soft tissue sarcoma of children, is currently classified into the following 4 subtypes: embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma, spindle cell/sclerosing rhabdomyosarcoma, and pleomorphic rhabdomyosarcoma, based on recent molecular genetic knowledge and morphologic features.

OBJECTIVE.—

To highlight the most recent advances of molecular genetic alterations, and to familiarize pathologists with most recent genotype and phenotype correlation in rhabdomyosarcoma.

DATA SOURCES.—

Data were derived from the World Health Organization Classification of Soft Tissue and Bone Tumors, fifth edition, recently published literature (PubMed), and clinical practice experience.

CONCLUSIONS.—

Current classification has been significantly impacted by genotype and phenotype correlation, especially with PAX-FOXO1 fusion-positive rhabdomyosarcoma versus fusion-negative rhabdomyosarcoma, and with emergence of 3 distinct new subtypes of spindle cell/sclerosing rhabdomyosarcoma. Although all rhabdomyosarcomas were considered to be a single diagnostic entity in the past, they are now considered to be a group of histologically similar but biologically diverse entities because their clinical behavior and underlying molecular alterations dramatically differ. This review outlines recent molecular genetic developments, corresponding morphologic features, and current challenges faced by pathologists in daily practice.

Methylation profiling reveals novel molecular classes of rhabdomyosarcoma

Rhabdomyosarcomas (RMS) represent a family of aggressive soft tissue sarcomas that present in both children and adults. Pathologic risk stratification for RMS has been based on histologic subtype, with poor outcomes observed in alveolar rhabdomyosarcoma (ARMS) and the adult-type pleomorphic rhabdomyosarcoma (PRMS) compared to embryonal rhabdomyosarcoma (ERMS). Genomic sequencing studies have expanded the spectrum of RMS, with several new molecularly defined entities, including fusion-driven spindle cell/sclerosing rhabdomyosarcoma (SC/SRMS) and MYOD1-mutant SC/SRMS. Comprehensive genomic analysis has previously defined the mutational and copy number spectrum for the more common ERMS and ARMS and revealed corresponding methylation signatures. Comparatively, less is known about epigenetic correlates for the rare SC/SRMS or PRMS histologic subtypes. Herein, we present exome and RNA sequencing, copy number analysis, and methylation profiling of the largest cohort of molecularly characterized RMS samples to date. In addition to ARMS and ERMS, we identify two novel methylation subtypes, one having SC/SRMS histology and defined by MYOD1 p. L122R mutations and the other matching adult-type PRMS. Selected tumors from adolescent patients grouped with the PRMS methylation class, expanding the age range of these rare tumors. Limited follow-up data suggest that pediatric tumors with MYOD1-mutations are associated with an aggressive clinical course.

PAX3-NCOA1 alveolar rhabdomyosarcoma of the tongue: A rare entity with challenging diagnosis and management

Alveolar rhabdomyosarcoma (ARMS) is associated with PAX3/PAX7-FOXO1 fusion, which confers specific clinic and biologic characteristics with inferior outcomes. A minority of tumors still histologically classified as "true" ARMS lack the canonical PAX-FOXO1 fusion but have new molecular alterations. We present the first case of PAX3-NCOA1 ARMS with clinical data and follow-up in a two-year-old girl with ARMS of the tongue and nodal extension, treated with chemotherapy, hemi glossectomy, lymph node dissection, and brachytherapy to conserve oral function and limit long-term sequelae. Given the rarity of such variant fusion in ARMS, international collaboration is required to evaluate its prognostic value.

A Comprehensive Circulating Tumor DNA Assay for Detection of Translocation and Copy-Number Changes in Pediatric Sarcomas

Most circulating tumor DNA (ctDNA) assays are designed to detect recurrent mutations. Pediatric sarcomas share few recurrent mutations but rather are characterized by translocations and copy-number changes. We applied Cancer Personalized Profiling by deep Sequencing (CAPP-Seq) for detection of translocations found in the most common pediatric sarcomas. We also applied ichorCNA to the combined off-target reads from our hybrid capture to simultaneously detect copy-number alterations (CNA). We analyzed 64 prospectively collected plasma samples from 17 patients with pediatric sarcoma. Translocations were detected in the pretreatment plasma of 13 patients and were confirmed by tumor sequencing in 12 patients. Two of these patients had evidence of complex chromosomal rearrangements in their ctDNA. We also detected copy-number changes in the pretreatment plasma of 7 patients. We found that ctDNA levels correlated with metastatic status and clinical response. Furthermore, we detected rising ctDNA levels before relapse was clinically apparent, demonstrating the high sensitivity of our assay. This assay can be utilized for simultaneous detection of translocations and CNAs in the plasma of patients with pediatric sarcoma. While we describe our experience in pediatric sarcomas, this approach can be applied to other tumors that are driven by structural variants.

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.

Clinical characteristics and outcomes of infants compared with children diagnosed with rhabdomyosarcoma: Analysis of surveillance, epidemiology and end results data from 2000 to 2016

BACKGROUND

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood, but occurs infrequently in infants (<1 year). Historically, infants with RMS have worse overall survival compared to other pediatric age groups.

AIM

This study aims to assess the clinical features and treatment factors associated with survival comparing infants to children aged 1-9 years diagnosed with RMS.

METHODS

Children aged <10 years diagnosed with RMS between 2000 and 2016 were identified using the SEER database. Descriptive statistics were used to assess demographic, clinical, and treatment characteristics of infants and children with RMS. Kaplan-Meier estimates and Cox proportional hazards regression were performed to assess for factors associated with survival.

RESULTS

Age <1 year was independently associated with an increased risk of mortality. Compared to children aged 1-9 years, fewer infants received standard of care therapy, that is, chemotherapy combined with local control (surgery and/or radiation; 86.8 vs. 75.7%; p = .009). In comparing the frequency of specific treatment modalities (used alone or in combination with other modalities), infants were less likely to receive radiation therapy (34.0 vs. 66.4%; p < .001) and more likely to receive surgery (68.9 vs. 57.5%; p = .02) than children aged 1-9 years. Across age groups, chemotherapy combined with local control was significantly associated with reduced mortality. Alveolar histology, metastatic disease, and Hispanic ethnicity were negatively associated with survival.

CONCLUSIONS

Age of <1 year was an independent risk factor for increased mortality from RMS compared to ages 1-9 years. Fewer infants were treated with chemotherapy combined with local control, the therapy associated with best survival in all age groups. Other factors contributing to differences in survival should be further explored.

Second-line therapy in young patients with relapsed or refractory orbital rhabdomyosarcoma

OBJECTIVE

Localized orbital rhabdomyosarcoma (oRMS) has an overall favourable prognosis with more than 90% of survival. Little is known about the best strategy in recurrent/refractory (R/R) cases. The purpose is to examine the characteristics of patients with R/R-oRMS, focusing on local therapy.

METHODS

This is bicentric retrospective study. Analysis is of young patients (<30 years) with R/R-oRMS who were treated from 1989 to 2018 at the Institut Curie and Gustave Roussy Cancer Campus, France.

RESULTS

Twenty-seven out of 162 patients (17%) with oRMS presented with R/R disease. 6 of these patients had alveolar RMS (22%), 3 of whom had initial parameningeal extension (11%). During first-line treatment, 18 patients (67%) had orbital radiotherapy. Median age at R/R was 10 years (ranges: 4-28) after a delay of 19 months from diagnosis (ranges: 3-40). Tumoral events were local relapses (22 cases), local progression (3 cases) or regional relapses (2 cases). Second-line treatments included chemotherapy (27 cases), radiotherapy (16 cases), surgery (exenteration; 8 cases) and metastasis/ nodal removal (3 cases). After a median follow-up of 99 months (range: 10-306), 4 patients died and 23 are in complete remission (CR) without treatment. One patient had subsequent relapse treated with exenteration and brachytherapy until a new tumour remission. Five-year event-free and overall survivals after first tumour event are, respectively, 84.4% (95% confidence interval: 71.5%-98.8%) and 85.8% (95% confidence interval: 72.1%-100.0%) CONCLUSION: R/R-oRMS is a rare situation. Second-line therapy is efficient in this location, sometime at the cost of lifesaving mutilating surgery. Second-line local therapy needs therefore to consider local radiotherapy if possible or complete wide surgery.

Alveolar rhabdomyosarcoma with regional nodal involvement: Results of a combined analysis from two cooperative groups

BACKGROUND

Treatment of children and adolescents with alveolar rhabdomyosarcoma (ARMS) and regional nodal involvement (N1) have been approached differently by North American and European cooperative groups. In order to define a better therapeutic strategy, we analyzed two studies conducted between 2005 and 2016 by the European paediatric Soft tissue sarcoma Study Group (EpSSG) and Children's Oncology Group (COG).

METHODS

We retrospectively identified patients with ARMS N1 enrolled in either EpSSG RMS2005 or in COG ARST0531. Chemotherapy in RMS2005 comprised ifosfamide + vincristine + dactinomycin + doxorubicin (IVADo), IVA and maintenance (vinorelbine, cyclophosphamide); in ARST0531, it consisted of either vincristine + dactinomycin + cyclophosphamide (VAC) or VAC alternating with vincristine + irinotecan (VI). Local treatment was similar in both protocols.

RESULTS

The analysis of the clinical characteristics of 239 patients showed some differences between study groups: in RMS2005, advanced Intergroup Rhabdomyosarcoma Study Group (IRS) and large tumors predominated. There were no differences in outcomes between the two groups: 5-year event-free survival (EFS), 49% (95% confidence interval [CI]: 39-59) and 44% (95% CI: 30-58), and overall survival (OS), 51% (95% CI: 41-61) and 53.6% (95% CI: 40-68) in RMS2005 and ARST0531, respectively. In RMS2005, EFS of patients with FOXO1-positive tumors was significantly inferior to those with FOXO1-negative (49.3% vs 73%, P = .034). In contrast, in ARST0531, EFS of patients with FOXO1-positive tumors was 45% compared with 43.8% for those with FOXO1-negative.

CONCLUSIONS

The outcome of patients with ARMS N1 was similar in both protocols. However, patients with FOXO1 fusion-negative tumors enrolled in RMS2005 showed a significantly better outcome, suggesting that different strategies of chemotherapy may have an impact in the outcome of this subgroup of patients.

Pathology of childhood rhabdomyosarcoma: A consensus opinion document from the Children's Oncology Group, European Paediatric Soft Tissue Sarcoma Study Group, and the Cooperative Weichteilsarkom Studiengruppe

The diagnosis and classification of rhabdomyosarcoma (RMS) has undergone several shifts over the last 30 years. While the main diagnostic categories remained the same, changes in the histologic criteria necessary for diagnosis, as well as varied reliance on immunohistochemical and molecular data over time, have created confusion, particularly regarding how these shifts impacted risk stratification and enrollment onto clinical trials. The goal of this report is to review the evolution and current status of RMS diagnosis, focusing on diagnostic criteria in the Children's Oncology Group (COG), the European Paediatric Soft Tissue Sarcoma Group (EpSSG), and the Cooperative Weichteilsarkom Studiengruppe (CWS). In addition, we emphasize research tools used to classify RMS and address biological questions within current clinical trials run by each group. The INternational Soft Tissue SaRcoma ConsorTium (INSTRuCT) initiative will maximize potential to optimize risk stratification by recognizing and accounting for differences in historical data and current practices.

Relapsed Rhabdomyosarcoma

Relapsed rhabdomyosarcoma (RMS) represents a significant therapeutic challenge. Nearly one-third of patients diagnosed with localized RMS and over two-thirds of patients with metastatic RMS will experience disease recurrence following primary treatment, generally within three years. Clinical features at diagnosis, including primary site, tumor invasiveness, size, stage, and histology impact likelihood of relapse and prognosis post-relapse. Aspects of initial treatment, including extent of surgical resection, use of radiotherapy, and chemotherapy regimen, are also associated with post-relapse outcomes, as are features of the relapse itself, including time to relapse and extent of disease involvement. Although there is no standard treatment for patients with relapsed RMS, several general principles, including tissue biopsy confirmation of diagnosis, assessment of post-relapse prognosis, determination of the feasibility of additional local control measures, and discussion of patient goals, should all be part of the approach to care. Patients with features suggestive of a favorable prognosis, which include those with botryoid RMS or stage 1 or group I embryonal RMS (ERMS) who have had no prior treatment with cyclophosphamide, have the highest chance of achieving long-term cure when treated with a multiagent chemotherapy regimen at relapse. Unfortunately, patients who do not meet these criteria represent the majority and have poor outcomes when treated with such regimens. For this group, strong consideration should be given for enrollment on a clinical trial.

Locoregional Control and Survival in Children, Adolescents, and Young Adults With Localized Head and Neck Alveolar Rhabdomyosarcoma-The French Experience

INTRODUCTION

The head and neck (HN) are the most frequent sites of pediatric rhabdomyosarcoma (RMS). Alveolar RMS (ARMS) represents ~20% of all RMS cases and frequently spread to lymph nodes (LNs). The aim was to report locoregional control, event-free survival (EFS), and overall survival (OS), according to clinical and pathological features, LN staging, and treatment modalities.

METHODS

The study included all patients prospectively enrolled in EpSSG RMS 2005 study under 21 years of age with localized HN ARMS and diagnosed between 2005 and 2016 in France. Medical data including imaging, surgical report, and radiation therapy planes were analyzed.

RESULTS

Forty-eight patients (median age 6 years; range 4 months-21 years), corresponding to 30 parameningeal and 18 non-parameningeal ARMS, were included. There were 33 boys (69%). Tumor locations included the following: orbit (n = 7) among which four cases had bone erosion, paranasal sinuses and nasal cavity (n = 16), deep facial spaces (n = 10), nasolabial fold (n = 8), and other non-parameningeal HN sites (n = 7). A fusion transcript of PAX3-FOXO1 or PAX7-FOXO1 was expressed in 33 of the 45 cases (73%) with molecular analysis. At diagnosis, 10 patients had primary resection of the primary tumor (PRPT) (none with microscopic complete resection) and 9 had LN staging. After induction chemotherapy, 26 patients (54%) had secondary resection of the primary tumor (SRPT) and 13 patients (27%) had cervical LN dissection. A total of 43 patients (90%) were treated with radiation therapy.With a median follow-up of 7 years (range 2-13 years), 5-year OS and EFS were 78% (95% CI, 63-88%) and 66% (95% CI, 51-78%), respectively. We observed 16 events (10 deaths): 4 local, 4 regional, 1 local and regional, and 7 metastatic. In univariate analysis, OS was only superior for patients under 10 years of age (p = 0.002), while FOXO1-negative ARMS, SRPT for parameningeal ARMS, and LN surgery were associated with significantly better EFS.

CONCLUSION

Our study confirms a better outcome for fusion-negative ARMS and ARMS in children under 10 years. Moreover, LN surgery and SRPT of parameningeal tumor may improve EFS of ARMS. Larger studies are needed to confirm our findings.

Survival outcomes of patients with localized FOXO1 fusion-positive rhabdomyosarcoma treated on recent clinical trials: A report from the Soft Tissue Sarcoma Committee of the Children's Oncology Group

BACKGROUND

The objective of this analysis was to evaluate the clinical factors influencing survival outcomes in patients with localized (clinical group I-III), FOXO1 fusion-positive rhabdomyosarcoma (RMS).

METHODS

Patients with confirmed FOXO1 fusion-positive RMS who were enrolled on 3 completed clinical trials for localized RMS were included in the analytic cohort. Outcomes were analyzed using the Kaplan-Meier method to estimate event-free survival (EFS) and overall survival (OS), and the curves were compared using the log-rank test. A Cox proportional hazards regression model was used to perform multivariate analysis of prognostic factors that were significant in the univariate analysis.

RESULTS

The estimated 4-year EFS and OS of 269 patients with localized, FOXO1 fusion-positive RMS was 53% (95% CI, 47%-59%) and 69% (95% CI, 63%-74%), respectively. Univariate analysis revealed that several known favorable clinical characteristics, including age at diagnosis between 1 and 9 years, complete surgical resection, tumor size ≤5 cm, favorable tumor site, absence of lymph node involvement, confinement to the anatomic site of origin, and PAX7-FOXO1 fusion, were associated with improved outcomes. Multivariate analysis identified older age (≥10 years) and large tumor size (>5 cm) as independent, adverse prognostic factors for EFS within this population, and patients who had both adverse features experienced substantially inferior outcomes.

CONCLUSIONS

Patients with localized, FOXO1 fusion-positive RMS can be further risk stratified based on clinical features at diagnosis, and older patients with large primary tumors have the poorest prognosis.

Pharmacologic Inhibition of Ezrin-Radixin-Moesin Phosphorylation is a Novel Therapeutic Strategy in Rhabdomyosarcoma

Intermediate and high-risk rhabdomyosarcoma (RMS) patients have poor prognosis with available treatment options, highlighting a clear unmet need for identification of novel therapeutic strategies. Ezrin-radixin-moesin (ERM) family members are membrane-cytoskeleton linker proteins with well-defined roles in tumor metastasis, growth, and survival. ERM protein activity is regulated by dynamic changes in the phosphorylation at a conserved threonine residue in their C-terminal actin-binding domain. Interestingly, ERM family member, ezrin, has elevated expression in the RMS tissue. Despite this, the translational scope of targeting ERM family proteins in these tumors through pharmacological inhibition has never been considered. This study investigates the inhibition of ERM phosphorylation using a small molecule pharmacophore NSC668394 as a potential strategy against RMS. Upon in vitro treatment with NSC668394, RMS cells exhibit a dose-dependent decrease in cell viability and proliferation, with induction of caspase-3 cleavage and apoptosis. siRNA-mediated knockdown of individual ERM protein expression revealed that each regulates RMS survival to a different degree. In vivo administration of NSC668394 in RMS xenografts causes significant decrease in tumor growth, with no adverse effect on body weight. Collectively, this study highlights the importance of the active conformation of ERM proteins in RMS progression and survival and supports pharmacologic inhibition of these proteins as a novel therapeutic approach.

Update on pediatric rhabdomyosarcoma: A report from the APSA Cancer Committee

BACKGROUND/PURPOSE

Rhabdomyosarcoma is the most common soft tissue sarcoma in children and young adults and requires multimodality treatment. The purpose of this review is to present an update on risk stratification as well as surgical and medical management strategies in pediatric rhabdomyosarcoma.

METHODS

A comprehensive review of the current literature on pediatric rhabdomyosarcoma, including the most recent Children's Oncology Group studies and several international collaboratives, was performed by the authors and key findings were summarized in the manuscript.

RESULTS

FOXO1 fusion status is a stronger prognostic factor than histology and is now used for risk stratification in treatment protocols. For assessment of regional nodal involvement, FDG-PET-CT shows poor sensitivity and specificity to detect histologically confirmed nodal metastasis. Thus, surgical assessment of regional lymph nodes is required for rhabdomyosarcoma of the extremities or trunk as well as paratesticular rhabdomyosarcoma in patients ≥10 years of age, although adherence to surgical guidelines remains poor. Hemiscrotectomy performed for scrotal violation in paratesticular rhabdomyosarcoma has not shown an improvement in event free survival and is not recommended.

CONCLUSIONS

Surgical and medical treatment strategies for rhabdomyosarcoma in children continue to evolve. This review provides current evidence-based treatment standards with an emphasis on surgical care.

TYPE OF STUDY

Review.

LEVEL OF EVIDENCE

Level IV.

Intratumoral Translocation Positive Heterogeneity in Pediatric Alveolar Rhabdomyosarcoma Tumors Correlates to Patient Survival Prognosis

Alveolar rhabdomyosarcoma (ARMS) is characterized by one of three translocation states: t(2;13) (q35;q14) producing PAX3-FOXO1, t(1;13) (p36;q14) producing PAX7-FOXO1, or translocation-negative. Tumors with t(2;13) are associated with greater disease severity and mortality than t(1;13) positive or translocation negative patients. Consistent with this fact, previous work concluded that a molecular analysis of RMS translocation status is essential for the accurate determination of prognosis and diagnosis. However, despite this knowledge, most diagnoses rely on histology and in some cases utilize fluorescence in situ hybridization (FISH) probes unable to differentiate between translocation products. Along these same lines, diagnostic RT-PCR analysis, which can differentiate translocation status, is unable to determine intratumoral translocation heterogeneity, making it difficult to determine if heterogeneity exists and whether correlations exist between this heterogeneity and patient outcomes. Using newly developed FISH probes, we demonstrate that intratumoral heterogeneity exists in ARMS tumors with respect to the presence or absence of the translocation product. We found between 3 and 98% of cells within individual tumor samples contained a translocation event with a significant inverse correlation (R² = 0.66, p = 0.001) between the extent of intratumoral translocation heterogeneity and failure-free survival of patients. Taken together, these results provide additional support for the inclusion of the molecular analysis of these tumors and expand on this idea to support determining the extent of intratumoral translocation heterogeneity in the diagnosis of ARMS to improve diagnostic and prognostic indicators for patients with these tumors.

A multidisciplinary approach to soft-tissue sarcoma of the extremities

INTRODUCTION

Soft-tissue sarcoma (STS) denotes a group of rare and highly heterogeneous malignant tumors of mesenchymal origin. Accurate histological diagnosis is critical for selecting appropriate treatment. Complete tumor resection is the primary treatment for STS, and the efficacies of radiotherapy and chemotherapy have been tested in the adjuvant setting to improve oncological outcomes. Because most STS lesions arise in the extremities, preserving limb function and managing limb impairment after radical local treatment represent significant challenges.

AREAS COVERED

This article reviews the current front-line treatments for patients with extremity STS and discusses the multidisciplinary team-based efforts needed to improve oncological outcomes and survivorship.

EXPERT OPINION

Given the rarity, variety, and complexity of STS, a multidisciplinary approach involving experts in various disciplines is vital for improving outcomes in patients ranging from diagnosis to survivorship. A major challenge is building a sustainable system in each region permitting all patients with extremity STS to be treated at high-volume centers with multidisciplinary teams dedicated to this rare and complex disease.

Do children and adolescents with completely resected alveolar rhabdomyosarcoma require adjuvant radiation? A report from the Children's Oncology Group

BACKGROUND

The role of adjuvant radiotherapy (RT) remains unclear in patients with localized, completely resected (group I) alveolar rhabdomyosarcoma (ARMS).

PROCEDURE

Patients with group I ARMS enrolled on any one of three prior Children's Oncology Group (COG) clinical trials (D9602, D9803, or ARST0531) were analyzed. All patients received systemic chemotherapy and 36 Gy adjuvant RT (if given) to the primary site at week 12 or week 4 for D9602/D9803 and ARST0531, respectively.

RESULTS

Thirty-six patients with group I ARMS were treated on D9602 (n = 6), D9803 (n = 17), or ARST0531 (n = 13), of whom 24 (67%) were male. The median age was 4.1 years (range, 0.8-45.8). Twenty (56%) patients had an unfavorable primary site, and 10 (28%) had tumors > 5 cm. FOXO1-fusion status was negative, positive, and unknown in 10 (28%), 15 (42%), and 11 (30%) tumors, respectively. Twenty-two (61%) patients received RT. Overall, the four-year event-free survival (EFS) and overall survival (OS) were 70.8% and 88.3%, respectively. Patients with FOXO1 positivity who received RT had superior EFS compared with those who did not (77.8% vs 16.7%; P = 0.03). Among 10 patients who were FOXO1 negative, the outcome was similar with or without RT.

CONCLUSIONS

Although limited by a small sample size, data from this study support the routine use of adjuvant RT in patients with FOXO1-positive disease even after complete resection. Additionally, omitting adjuvant RT is rational for patients with FOXO1-negative ARMS and will be prospectively investigated in the current COG trial ARST1431.

MRI of Rhabdomyosarcoma and Other Soft-Tissue Sarcomas in Children

Soft-tissue sarcomas in children comprise a heterogeneous group of entities with variable manifestation depending on the age of the patient and the location of the tumor. MRI is the modality of choice for evaluating musculoskeletal soft-tissue tumors and plays a paramount role in both initial diagnosis and assessment of tumor response during and after treatment. Conventional MRI sequences, such as T1- and T2-weighted imaging, offer morphologic information, which is important for localizing the lesion and describing anatomic relationships but not accurate for determining its malignant or benign nature and may be limited in differentiating tumor response from therapy-related changes. Advanced multiparametric MRI offers further functional information that can help with these tasks by using different imaging sequences and biomarkers. The authors present the role of MRI in rhabdomyosarcoma and other soft-tissue sarcomas in children, emphasizing a multiparametric approach with focus on the utility and potential added value of diffusion-weighted imaging (DWI) and dynamic contrast-enhanced MRI in characterization and staging, determination of pretreatment extent, and evaluation of tumor response and recurrence after treatment. ^©RSNA, 2020.

Prognostic Value of Circulating IGFBP2 and Related Autoantibodies in Children with Metastatic Rhabdomyosarcomas

Insulin-like growth factor-binding protein 2 (IGFBP2) is a tumor-associated protein measurable in patients’ biopsies and blood samples. Increased IGFBP2 expression correlates with tumor severity in rhabdomyosarcoma (RMS). Thus, we examined the plasmatic IGFBP2 levels in 114 RMS patients and 15 healthy controls by ELISA assay in order to evaluate its value as a plasma biomarker for RMS. Additionally, we looked for the presence of a humoral response against IGBFP2 protein measurable by the production of anti-IGFBP2 autoantibodies. We demonstrated that both circulating IGFBP2 protein and autoantibodies were significantly higher in RMS patients with respect to controls and their combination showed a better discriminative capacity. IGFBP2 protein identified metastatic patients with worse event-free survival, whereas both IGFBP2 and anti-IGFBP2 antibodies negatively correlated with overall survival. Our study suggests that IGFBP2 and anti-IGFBP2 antibodies are useful for diagnostic and prognostic purposes, mainly as independent negative prognostic markers in metastatic patients. This is the first study that reports a specific humoral response in RMS plasma samples and proves the value of blood-based biomarkers in improving risk assessment and outcome of metastatic RMS patients.

Extensive Clonal Branching Shapes the Evolutionary History of High-Risk Pediatric Cancers

Darwinian evolution of tumor cells remains underexplored in childhood cancer. We here reconstruct the evolutionary histories of 56 pediatric primary tumors, including 24 neuroblastomas, 24 Wilms tumors, and 8 rhabdomyosarcomas. Whole-genome copy-number and whole-exome mutational profiling of multiple regions per tumor were performed, followed by clonal deconvolution to reconstruct a phylogenetic tree for each tumor. Overall, 88% of the tumors exhibited genetic variation among primary tumor regions. This variability typically emerged through collateral phylogenetic branching, leading to spatial variability in the distribution of more than 50% (96/173) of detected diagnostically informative genetic aberrations. Single-cell sequencing of 547 individual cancer cells from eight solid pediatric tumors confirmed branching evolution to be a fundamental underlying principle of genetic variation in all cases. Strikingly, cell-to-cell genetic diversity was almost twice as high in aggressive compared with clinically favorable tumors (median Simpson index of diversity 0.45 vs. 0.88; P = 0.029). Similarly, a comparison of multiregional sampling data from a total of 274 tumor regions showed that new phylogenetic branches emerge at a higher frequency per sample and carry a higher mutational load in high-risk than in low-risk tumors. Timelines based on spatial genetic variation showed that the mutations most influencing relapse risk occur at initiation of clonal expansion in neuroblastoma and rhabdomyosarcoma, whereas in Wilms tumor, they are late events. Thus, from an evolutionary standpoint, some high-risk childhood cancers are born bad, whereas others grow worse over time. SIGNIFICANCE: Different pediatric cancers with a high risk of relapse share a common generic pattern of extensively branching evolution of somatic mutations. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/7/1512/F1.large.jpg.

Soft Tissue Special Issue: Skeletal Muscle Tumors: A Clinicopathological Review

Skeletal muscle tumors are classified into rhabdomyoma and embryonal, alveolar, spindle cell/sclerosing and pleomorphic rhabdomyosarcoma according to WHO classifications of tumors. These tumors arise mostly in the head and neck and, in childhood, represent the largest subset of soft tissue tumors. Although these skeletal muscle tumors show common immunoexpression of two myogenic regulatory factors, MyoD1 and myogenin, their molecular biological backgrounds are quite different. Therefore, treatment regimens vary a great deal depending on the histological subtype. Histopathologically, rhabdomyoma is characterized by well-demarcated lesions with no invasion of the surrounding tissue. Embryonal rhabdomyosarcoma is composed of primitive mesenchymal cells in various stages of myogenesis and shows heterogeneous nuclear staining for myogenin. Alveolar rhabdomyosarcoma, on the other hand, shows a proliferation of uniform primitive round cells arranged in alveolar patterns. The tumor cells at the periphery of alveolar structures adhere in a single layer to the fibrous septa. Diffuse and strong nuclear immunoexpression for myogenin is observed. In genetic backgrounds, almost all alveolar rhabdomyosarcomas contain a characteristic fusion gene such as PAX3/7-FOXO1. Spindle cell/sclerosing rhabdomyosarcoma is characterized by fascicularly arranged spindle-shaped cells or dense hyalinized collagenous matrix. NCOR2- or VGLL2-related gene fusions or MYOD1 (p.L122R) mutation is commonly recognized. Epithelioid rhabdomyosarcoma is a rare variant of rhabdomyosarcoma that shows a proliferation of epithelioid tumor cells having large vesicular nuclei, prominent nucleoli, and amphophilic to eosinophilic cytoplasm arranged in sheets. As these characteristic histological and molecular features are present in each subtype, it is possible to diagnose skeletal muscle tumors accurately.

Current and Future Treatment Strategies for Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children, and can be subcategorized histologically and/or based on PAX-FOXO1 fusion gene status. Over the last four decades, there have been no significant improvements in clinical outcomes for advanced and metastatic RMS patients, underscoring a need for new treatment options for these groups. Despite significant advancements in our understanding of the genomic landscape and underlying biological mechanisms governing RMS that have informed the identification of novel therapeutic targets, development of these therapies in clinical trials has lagged far behind. In this review, we summarize the current frontline multi-modality therapy for RMS according to pediatric protocols, highlight emerging targeted therapies and immunotherapies identified by preclinical studies, and discuss early clinical trial data and the implications they hold for future clinical development.

Spindle and Round Cell Sarcoma With EWSR1-PATZ1 Gene Fusion: A Sarcoma With Polyphenotypic Differentiation

The evolving classification of round cell sarcomas is driven by molecular alterations. EWSR1-PATZ1 fusion positive spindle and round cell sarcoma is one such new tumor entity. Herein, we report 2 EWSR1-PATZ1 fusion positive spindle and round cell sarcomas with overlapping histologic features and polyphenotypic differentiation. The intra-abdominal tumors affected female patients, 31-and 53-year old. Both tumors showed sheets and nests of round to spindle cells, fine chromatin, tiny conspicuous nucleoli, moderate cytoplasm, and thick bands of intratumoral fibrosis. On immunohistochemistry, both tumors showed positivity for CD99, desmin, myogenin, MyoD1, S100, Sox10, CD34, and GFAP and were negative for keratin. Fluorescence in situ hybridization revealed rearrangement at EWSR1 locus. Next-generation sequencing-based RNA fusion assay revealed EWSR1-PATZ1 fusion in both cases. EWSR1-PATZ1 fusion positive spindle and round cell sarcomas show abundant intratumoral fibrosis and polyphenotypic differentiation, thus mimicking a range of tumors including desmoplastic small round cell tumor. The precise classification of this spindle and round cell sarcoma and its relationship to the Ewing sarcoma family of tumors remains to be determined.

The PAX3-FOXO1 oncogene alters exosome miRNA content and leads to paracrine effects mediated by exosomal miR-486

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. The alveolar subtype (ARMS) is clinically more aggressive, and characterized by an oncogenic fusion protein PAX3-FOXO1 that drives oncogenic cellular properties. Exosomes are small, secreted vesicles that affect paracrine signaling. We show that PAX3-FOXO1 transcript alters exosome content of C2C12 myoblasts, leading to pro-tumorigenic paracrine effects in recipient cells. Microarray analysis revealed alteration in miRNA content of exosomes, affecting cellular networks involved in cell metabolism, growth signaling, and cellular invasion. Overexpression and knockdown studies showed that miR-486-5p is an effector of PAX3-FOXO1, and mediates its paracrine effects in exosomes, including promoting recipient cell migration, invasion, and colony formation. Analysis of human RMS cells showed miR-486-5p is enriched in both cells and exosomes, and to a higher extent in ARMS subtypes. Analysis of human serum samples showed that miR-486-5p is enriched in exosomes of patients with RMS, and follow-up after chemotherapy showed decrease to control values. Our findings identify a novel role of both PAX3-FOXO1 and its downstream effector miR-486-5p in exosome-mediated oncogenic paracrine effects of RMS, and suggest its possible use as a biomarker.

Gene fusions and chimeric RNAs, and their implications in cancer

Gene fusions are appreciated as ideal cancer biomarkers and therapeutic targets. Chimeric RNAs are traditionally thought to be products of gene fusions, and thus, also cancer-specific. Recent research has demonstrated that chimeric RNAs can be generated by intergenic splicing in the absence of gene fusion, and such chimeric RNAs are also found in normal physiology. These new findings challenge the traditional theory of chimeric RNAs exclusivity to cancer, and complicates use of chimeric RNAs in cancer detection. Here, we provide an overview of gene fusions and chimeric RNAs, and emphasize their differences. We note that gene fusions are able to generate chimeric RNAs in accordance with the central dogma of biology, and that chimeric RNAs may also be able to influence the generation of the gene fusions per the “horse before the cart” hypothesis. We further expand upon the “horse before the cart” hypothesis, summarizing current evidence in support of the theory and exploring its potential impact on the field.

Refinement of risk stratification for childhood rhabdomyosarcoma using FOXO1 fusion status in addition to established clinical outcome predictors: A report from the Children's Oncology Group

Background

Previous studies of the prognostic importance of FOXO1 fusion status in patients with rhabdomyosarcoma (RMS) have had conflicting results. We re‐examined risk stratification by adding FOXO1 status to traditional clinical prognostic factors in children with localized or metastatic RMS.

Methods

Data from six COG clinical trials (D9602, D9802, D9803, ARST0331, ARTS0431, ARST0531; two studies each for low‐, intermediate‐ and high‐risk patients) accruing previously untreated patients with RMS from 1997 to 2013 yielded 1727 evaluable patients. Survival tree regression for event‐free survival (EFS) was conducted to recursively select prognostic factors for branching and split. Factors included were age, FOXO1, clinical group, histology, nodal status, number of metastatic sites, primary site, sex, tumor size, and presence of metastases in bone/bone marrow, soft tissue, effusions, lung, distant lymph nodes, and other sites. Definition and outcome of the proposed risk groups were compared to existing systems and cross‐validated results.

Results

The 5‐year EFS and overall survival (OS) for evaluable patients were 69% and 79%, respectively. Extent of disease (localized versus metastatic) was the first split (EFS 73% vs 30%; OS 84% vs. 42%). FOXO1 status (positive vs negative) was significant in the second split both for localized (EFS 52% vs 78%; OS 65% vs 88%) and metastatic disease (EFS 6% vs 46%; OS 19% vs 58%).

Conclusions

After metastatic status, FOXO1 status is the most important prognostic factor in patients with RMS and improves risk stratification of patients with localized RMS. Our findings support incorporation of FOXO1 status in risk stratified clinical trials.

Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and represents a high-grade neoplasm of skeletal myoblast-like cells. Decades of clinical and basic research have gradually improved our understanding of the pathophysiology of RMS and helped to optimize clinical care. The two major subtypes of RMS, originally characterized on the basis of light microscopic features, are driven by fundamentally different molecular mechanisms and pose distinct clinical challenges. Curative therapy depends on control of the primary tumour, which can arise at many distinct anatomical sites, as well as controlling disseminated disease that is known or assumed to be present in every case. Sophisticated risk stratification for children with RMS incorporates various clinical, pathological and molecular features, and that information is used to guide the application of multifaceted therapy. Such therapy has historically included cytotoxic chemotherapy as well as surgery, ionizing radiation or both. This Primer describes our current understanding of RMS epidemiology, disease susceptibility factors, disease mechanisms and elements of clinical care, including diagnostics, risk-based care of newly diagnosed and relapsed disease and the prevention and management of late effects in survivors. We also outline potential opportunities to further translate new biological insights into improved clinical outcomes.

Rhabdomyosarcoma and Extraosseous Ewing Sarcoma

Rhabdomyosarcoma (RMS) is a malignant tumor that represents the most common form of pediatric soft tissue sarcoma. It arises from mesenchymal origin and forms part of the group of small round blue cell tumors of childhood. It has a constant annual incidence of 4.5 cases per 1,000,000 children. The known histological diagnosis of the two major subtypes (embryonal and alveolar) has been recently enhanced by tumor biological markers and molecular differentiation diagnostic tools that have improved not only the updated classification based on risk stratification, but also the treatment approach based on the clinical group. Ewing sarcoma (ES) is a round cell tumor, highly malignant and poorly differentiated that is currently the second most common malignant bone tumor in children. In rare instances, it develops from an extraskeletal origin, classified as extraosseous Ewing sarcoma (EES). We provide an updated, evidence-based and comprehensive review of the molecular diagnosis, clinical and diagnostic approach and a multidisciplinary medical and surgical management according to the latest standard of care for the treatment of pediatric RMS and EES.

Fifty years of rhabdomyosarcoma studies on both sides of the pond and lessons learned

We review and summarize the highlights of almost five decades of cooperative group trials in rhabdomyosarcoma on both sides of the Atlantic, concentrating on chemotherapy regimens, what has been learned, and where remaining challenges are. The most important achievements have been to decrease or omit the dose of alkylator therapy for many patients, to clarify after much controversy that doxorubicin does not improve the outcome of patients even in the highest risk groups, and to show that high dose chemotherapy and stem cell rescue do not improve the outcome of the highest risk patients. In North America, vincristine/actinomycin/cyclophosphamide (VAC) remains an important part of therapy, whereas in Europe the alkylating agent of choice is ifosfamide. The highest risk patients, namely those with the poorest prognostic score, have had no improvement in outcome since the first cooperative group trial in 1972 and remain the greatest challenge. Philosophical differences between European and North American strategies still revolve somewhat around the total burden of therapy received, that is should certain groups of patients be spared aggressive local control in order to reduce late effects, recognizing that it is not possible to identify priori the children that can be cured with this approach exposing the whole population to a higher risk of relapse. Collaboration and joining resources may help answer some difficult questions.

Chest wall reconstruction after tumor resection

Pediatric chest wall tumors are rare. Malignancies predominate of which sarcomas are the most common. Their resection and the subsequent reconstruction of the chest wall has been a surgical challenge since Dr. Frederick W. Parham published his first comprehensive account on the subject in 1898. Chest wall reconstruction is age, site and pathology dependent, must preserve long term function and cosmesis, must accommodate future growth and development, and must not be a hindrance to adjuvant radiotherapy. Bony reconstruction can be relatively simple or complex involving combinations of synthetic meshes, bioprosthetic materials, steel or titanium constructs, autografts, homografts and porcine or bovine xenografts. Soft tissue coverage can be achieved with direct closure, skin grafts, local advancement flaps, pedicled or free myocutaneous or osseomyocutaneous flaps or a combination of these. Complications to be avoided include scoliosis, pain and activity restriction, restrictive pulmonary deficits and interference with adjuvant radiotherapy which may result in tumor recurrence. Advances in cancer therapy have improved short- and long-term survival but significant functional and cosmetic challenges remain particularly for large chest wall defects in the very young. The future may lie with absorbable semi-rigid meshes, biointegratable acellular homografts and xenografts, demineralized bone matrices and bone marrow stromal cells, the patient's own lab-grown stem-cell based vascularized osseomyocutaneous chest wall grafts or the obsolescence of surgical resection altogether in the age of targeted anti-tumor and immune based therapy.

Cytologic diagnosis of round cell sarcomas in the era of ancillary testing: an updated review

Round cell sarcomas constitute a large proportion of "small round blue cell tumors," which encompass a broad differential diagnosis and can be difficult to distinguish on cytomorphologic grounds alone. Numerous pathogenetic insights and advances in ancillary testing in soft tissue pathology over the last several decades have made accurate classification of soft tissue neoplasms increasingly feasible. Immunohistochemistry and genetic/molecular testing can now be performed on all cytologic preparations, including unstained smears, needle rinses, cell blocks, and liquid-based preparations, and this has greatly increased our diagnostic abilities. Nevertheless, there remain numerous diagnostic challenges, including variable sensitivity and specificity of available immunohistochemical markers, overlapping immunophenotypes between entities, and "promiscuity" of genetic alterations such as EWSR1 rearrangements, present in a multitude of tumor types. Herein we provide a review on the cytologic, immunohistochemical, and genetic features of the more frequently encountered round cell sarcomas, as well as recently described entities, with an emphasis on diagnostic pitfalls and judicious use of ancillary studies.

Histology, fusion status, and outcome in metastatic rhabdomyosarcoma: A report from the Children's Oncology Group

BACKGROUND

Distinguishing alveolar rhabdomyosarcoma (ARMS) from embryonal rhabdomyosarcoma (ERMS) has historically been of prognostic and therapeutic importance. However, classification has been complicated by shifting histologic criteria required for an ARMS diagnosis. Children's Oncology Group (COG) studies after IRS-IV, which included the height of this diagnostic shift, showed both an increased number of ARMS and an increase in the proportion of fusion-negative ARMS. Following diagnostic standardization and histologic re-review of ARMS cases enrolled during this era, analysis of low-risk (D9602) and intermediate-risk (D9803) rhabdomyosarcoma (RMS) studies showed that fusion status rather than histology best predicts prognosis for patients with RMS. This analysis remains to be completed for patients with high-risk RMS.

PROCEDURE

We re-reviewed cases on high-risk COG studies D9802 and ARST0431 with an enrollment diagnosis of ARMS. We compared the event-free survival (EFS) and overall survival by histology, PAX-FOXO1 fusion, and clinical risk factors (Oberlin score) for patients with metastatic RMS using the log-rank test.

RESULTS

Histology re-review resulted in reclassification as ERMS for 12% of D9802 cases and 5% of ARST0431 cases. Fusion-negative RMS had a superior EFS to fusion-positive RMS; however, poorer outcome for metastatic RMS was most related to clinical risk factors including age, primary site, and number of metastatic sites.

CONCLUSIONS

In contrast to low- or intermediate-risk RMS, in metastatic RMS, clinical risk factors have the most impact on patient outcome. PAX-FOXO1 fusion is more common in patients with a high Oberlin score, but fusion status is not an independent biomarker of prognosis.

Molecular diagnostics in the management of rhabdomyosarcoma

INTRODUCTION

A classification of rhabdomyosarcoma (RMS) with prognostic relevance has primarily relied on clinical features and histologic classification as either embryonal or alveolar RMS. The PAX3-FOXO1 and PAX7-FOXO1 gene fusions occur in 80% of cases with the alveolar subtype and are more predictive of outcome than histologic classification. Identifying additional molecular hallmarks that further subclassify RMS is an active area of research. Areas Covered: The authors review the current state of the PAX3-FOXO1 and PAX7-FOXO1 fusions as prognostic biomarkers. Emerging biomarkers, including mRNA expression profiling, MYOD1 mutations, RAS pathway mutations and gene fusions involving NCOA2 or VGLL2 are also reviewed. Expert commentary: Strategies for modifying RMS risk stratification based on molecular biomarkers are emerging with the potential to transform the clinical management of RMS, ultimately improving patient outcomes by tailoring therapy to predicted patient risk and identifying targets for novel therapies.

A clinicopathologic study of head and neck rhabdomyosarcomas showing FOXO1 fusion-positive alveolar and MYOD1-mutant sclerosing are associated with unfavorable outcome

BACKGROUND

Based on their distinctive histologic and genetic features, the latest WHO classification of soft tissue tumors includes four pathologic variants of rhabdomyosarcoma (RMS): embryonal (ERMS), alveolar (ARMS), spindle cell-sclerosing (SRMS-ScRMS) and pleomorphic RMS. The aim of this study focused on a detailed clinicopathologic and survival analysis of head and neck RMS (HNRMS) using the latest pathologic and molecular criteria reflecting this new subclassification in a large cohort.

PATIENTS AND METHODS

Patients managed for HNRMS in our institution (1996-2015) were analyzed. The presence of a FOXO1 fusion was required for the classification of ARMS. MYOD1 mutations in SRMS-ScRMS were tested when material available. Univariate and multivariate analyses were performed to evaluate variables related to overall survival (OS).

RESULTS

Ninety-nine HNRMS patients (52 males and 47 females, mean of 16years) were included in the study after pathologic re-review. The most common location was parameningeal (PM) (n=64), followed by non-orbital/non-PM (n=25) and orbital (n=10). There were 53 ERMS, 33 fusion-positive ARMS and 13 SRMS-ScRMS [SRMS (8); ScRMS (5)]. The 5-year OS rate for ERMS patients was significantly higher (82%) compared to ARMS (53%) and SRMS-ScRMS (50%) [SRMS (75%); ScRMS (30%)]. Univariate analysis showed that survival was dependent on histology (P=0.012), tumor size >5cm (P<0.001), regional lymph node involvement (P=0.002), metastasis at initial presentation (P<0.001), stage (P<0.001), and recurrence (P=0.002). Multivariate analysis confirmed histologic subtype to be significant (P=0.043).

CONCLUSION

Our findings reinforce that HNRMS is a heterogenous disease with ARMS and SRMS-ScRMS having an equally unfavorable outcome.