MYOD1-mutant spindle cell and sclerosing rhabdomyosarcoma: an aggressive subtype irrespective of age. A reappraisal for molecular classification and risk stratification

Molecular Alterations in Pediatric Solid Tumors

Pediatric tumors can be divided into hematologic malignancies, central nervous system tumors, and extracranial solid tumors of bone, soft tissue, or other organ systems. Molecular alterations that impact diagnosis, prognosis, treatment, and familial cancer risk have been described in many pediatric solid tumors. In addition to providing a concise summary of clinically relevant molecular alterations in extracranial pediatric solid tumors, this review discusses conventional and next-generation sequencing-based molecular techniques, relevant tumor predisposition syndromes, and the increasing integration of molecular data into the practice of diagnostic pathology for children with solid tumors.

Rhabdomyosarcoma: Updates on classification and the necessity of molecular testing beyond immunohistochemistry

Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children and adolescents under the age of 20. The current World Health Organization (WHO) classification for soft tissue and bone tumors recognizes 4 distinct subtypes of RMS based on clinicopathological and molecular genetic features: embryonal, alveolar, spindle cell/sclerosing and pleomorphic subtypes. However, with the increased use of molecular techniques, the classification of rhabdomyosarcoma has been evolving rapidly. New subtypes such as osseus RMS harboring TFCP2/NCOA2 fusions or RMS arising in inflammatory rhabdomyoblastic tumor have been emerging within the last decade, adding to the complexity of diagnosing skeletal muscle tumors. This review article provides an overview of classically recognized distinctive subtypes as well as new, evolving subtypes and discusses important morphologic, immunophenotypic and molecular genetic features of each subtype including recommendations for a diagnostic approach of malignant skeletal muscle neoplasms.

Multifaceted Spindle Cell/Sclerosing Rhabdomyosarcoma With Role of Immunohistochemistry in Avoiding Misdiagnosis: A Multi-Institutional Study of 45 Distinct Tumors

Background. Spindle cell/sclerosing rhabdomyosarcoma is a rare neoplasm and has an aggressive clinical course. Because of its rarity, we performed a multi-institutional collaboration to comprehend the overarching clinical, histopathological, and immunohistochemical characteristics of a cohort of spindle cell/sclerosing rhabdomyosarcoma. Materials and Methods. Forty-five patients with spindle cell/sclerosing rhabdomyosarcoma were identified. Demographics, clinical, histopathological, and immunohistochemistry data were reviewed and recorded. Results. The patients' age ranged from 1 to 85 years with a male to female ratio of 1.2:1. There were 15 children/adolescents and 30 adults. Eighteen (40%) tumors were located in the head and neck region. Twenty-four (53%) tumors displayed a bimorphic cellular arrangement with hypercellular areas having short, long, and sweeping fascicular and herringbone pattern, and hypocellular areas with stromal sclerosis and associated hyalinized and/or chondromyxoid matrix. Histomorphological differentials considered were leiomyosarcoma, malignant peripheral nerve sheath tumor, fibrosarcoma, nodular fasciitis, liposarcoma, synovial sarcoma, sarcomatoid carcinoma, solitary fibrous tumor, dermatofibrosarcoma protuberans, and schwannoma. Six tumors exhibited marked stromal sclerosis. The myogenic nature was confirmed by immunohistochemistry. Positivity for at least one skeletal muscle-associated marker (MyoD1 and/or myogenin) was observed. Conclusion. Spindle cell/sclerosing rhabdomyosarcoma diagnosis can be challenging as a number of malignant spindle cell neoplasm mimic this entity. Thus a correct diagnosis requires immunohistochemical work up with a broad panel of antibodies. In view of rarity of this neoplasm, further studies on a large cohort of patients with clinical follow-up data are needed for a better understanding of this tumor.

Embryonal and alveolar rhabdomyosarcoma in adolescents/young adults, adults and older adults: a population-based cohort study

BACKGROUND

The clinical characteristics, outcomes, and prognostic factors of adult embryonal rhabdomyosarcomas (ERMS) and alveolar rhabdomyosarcomas (ARMS), particularly the differences among adolescents/young adults (AYA), adults, and older adults, remain unclear. We assessed the clinicopathological features and survival outcomes of adult patients with ERMS and ARMS in Japan and to compare these features among AYA, adult, and older adult patients.

METHODS

We retrospectively analyzed data from the Bone and Soft Tissue Tumor Registry of Japan and enrolled patients aged ≥15 years with ERMS and ARMS. Disease-specific overall survival (DOS) was estimated using the Kaplan-Meier method, and a Cox regression model was used to identify prognostic factors.

RESULTS

Among 184 patients with ERMS and ARMS (median age, 27 years; interquartile range, 18-49 years), a high rate of distant and regional nodal metastases was initially observed in 65 (35%) and 66 (36%) cases, respectively. Older age and distant metastasis at first presentation were statistically poor prognostic factors, and histological subtype and site of tumor origin were not associated with DOS. In patients with localized ERMS and ARMS, older age and nodal metastasis were poor prognostic factors; the 5-year DOS rates of patients with and without nodal metastasis were 23% and 72%, respectively.

CONCLUSIONS

Older patients with rhabdomyosarcoma had a dismal prognosis, and distant metastasis was a poor prognostic factor. The prognostic factors differed between adult and pediatric patients with rhabdomyosarcoma; biological analyses, such as genome analysis of adult rhabdomyosarcoma and clinical trials with pediatric oncologists, are needed to improve the prognosis of adult rhabdomyosarcoma.

Therapeutic Targeting of DNA Repair Pathways in Pediatric Extracranial Solid Tumors: Current State and Implications for Immunotherapy

DNA damage is fundamental to tumorigenesis, and the inability to repair DNA damage is a hallmark of many human cancers. DNA is repaired via the DNA damage repair (DDR) apparatus, which includes five major pathways. DDR deficiencies in cancers give rise to potential therapeutic targets, as cancers harboring DDR deficiencies become increasingly dependent on alternative DDR pathways for survival. In this review, we summarize the DDR apparatus, and examine the current state of research efforts focused on identifying vulnerabilities in DDR pathways that can be therapeutically exploited in pediatric extracranial solid tumors. We assess the potential for synergistic combinations of different DDR inhibitors as well as combinations of DDR inhibitors with chemotherapy. Lastly, we discuss the immunomodulatory implications of targeting DDR pathways and the potential for using DDR inhibitors to enhance tumor immunogenicity, with the goal of improving the response to immune checkpoint blockade in pediatric solid tumors. We review the ongoing and future research into DDR in pediatric tumors and the subsequent pediatric clinical trials that will be critical to further elucidate the efficacy of the approaches targeting DDR.

Spindle cell rhabdomyosarcomas: With TFCP2 rearrangements, and novel EWSR1::ZBTB41 and PLOD2::RBM6 gene fusions. A study of five cases and review of the literature

AIMS

Spindle-cell/sclerosing rhabdomyosarcomas (SS-RMS) are clinically and genetically heterogeneous. They include three well-defined molecular subtypes, of which those with EWSR1/FUS::TFCP2 rearrangements were described only recently. This study aimed to evaluate five new cases of SS-RMS and to perform a clinicopathological and statistical analysis of all TFCP2-rearranged SS-RMS described in the English literature to more comprehensively characterize this rare tumour type.

METHODS AND RESULTS

Cases were retrospectively selected and studied by immunohistochemistry, fluorescence in situ hybridization with EWSR1/FUS and TFCP2 break-apart probes, next-generation sequencing (Archer FusionPlex Sarcoma kit and TruSight RNA Pan-Cancer Panel). The PubMed database was searched for relevant peer-reviewed English reports. Five cases of SS-RMS were found. Three cases were TFCP2 rearranged SS-RMS, having FUSex6::TFCP2ex2 gene fusion in two cases and triple gene fusion EWSR1ex5::TFCP2ex2, VAX2ex2::ALKex2 and VAX2intron2::ALKex2 in one case. Two cases showed rhabdomyoblastic differentiation and spindle-round cell/sclerosing morphology, but were characterized by novel genetic fusions including EWSR1ex8::ZBTB41ex7 and PLOD2ex8::RBM6ex7, respectively. In the statistical analysis of all published cases, CDKN2A or ALK alterations, the use of standard chemotherapy and age at presentation in the range of 18-24 years were negatively correlated to overall survival.

CONCLUSION

EWSR1/FUS::TFCP2-rearranged SS-RMS is a rare rhabdomyosarcoma subtype, affecting predominantly young adults with average age at presentation 34 years (median 29.5 years; age range 7-86 years), with a predilection for craniofacial bones, rapid clinical course with frequent bone and lung metastases, and poor prognosis (3-year overall survival rate 28%).

Germline Genetic Testing and Survival Outcomes Among Children With Rhabdomyosarcoma: A Report From the Children's Oncology Group

Importance

Determining the impact of germline cancer-predisposition variants (CPVs) on outcomes could inform novel approaches to testing and treating children with rhabdomyosarcoma.

Objective

To assess whether CPVs are associated with outcome among children with rhabdomyosarcoma.

Design, Setting, and Participants

In this cohort study, data were obtained for individuals, aged 0.01-23.23 years, newly diagnosed with rhabdomyosarcoma who were treated across 171 Children's Oncology Group sites from March 15, 1999, to December 8, 2017. Data analysis was performed from June 16, 2021, to May 15, 2023.

Exposure

The presence of a CPV in 24 rhabdomyosarcoma-associated cancer-predisposition genes (CPGs) or an expanded set of 63 autosomal-dominant CPGs.

Main Outcomes and Measures

Overall survival (OS) and event-free survival (EFS) were the main outcomes, using the Kaplan-Meier estimator to assess survival probabilities and the Cox proportional hazards regression model to adjust for clinical covariates. Analyses were stratified by tumor histology and the fusion status of PAX3 or PAX7 to the FOXO1 gene.

Results

In this study of 580 individuals with rhabdomyosarcoma, the median patient age was 5.9 years (range, 0.01-23.23 years), and the male-to-female ratio was 1.5 to 1 (351 [60.5%] male). For patients with CPVs in rhabdomyosarcoma-associated CPGs, EFS was 48.4% compared with 57.8% for patients without a CPV (P = .10), and OS was 53.7% compared with 65.3% for patients without a CPV (P = .06). After adjustment, patients with CPVs had significantly worse OS (adjusted hazard ratio [AHR], 2.49 [95% CI, 1.39-4.45]; P = .002), and the outcomes were not better among patients with embryonal histology (EFS: AHR, 2.25 [95% CI, 1.25-4.06]; P = .007]; OS: AHR, 2.83 [95% CI, 1.47-5.43]; P = .002]). These associations were not due to the development of a second malignant neoplasm, and importantly, patients with fusion-negative rhabdomyosarcoma who harbored a CPV had similarly inferior outcomes as patients with fusion-positive rhabdomyosarcoma without CPVs (EFS: AHR, 1.35 [95% CI, 0.71-2.59]; P = .37; OS: AHR, 1.71 [95% CI, 0.84-3.47]; P = .14). There were no significant differences in outcome by CPV status of the 63 CPG set.

Conclusions and Relevance

This cohort study identified a group of patients with embryonal rhabdomyosarcoma who had a particularly poor outcome. Other important clinical findings included that individuals with TP53 had poor outcomes independent of second malignant neoplasms and that patients with fusion-negative rhabdomyosarcoma who harbored a CPV had outcomes comparable to patients with fusion-positive rhabdomyosarcoma. These findings suggest that germline CPV testing may aid in clinical prognosis and should be considered in prospective risk-based clinical trials.

Prognostic and predictive biomarkers in paediatric solid tumours

Characterisation of histological, immunohistochemical and molecular prognostic and predictive biomarkers has contributed significantly to precision medicine and better outcomes in the management of paediatric solid tumours. Prognostic biomarkers allow predictions to be made regarding a tumour's aggressiveness and clinical course, whereas predictive biomarkers help determine responses to a specific treatment. This review summarises prognostic biomarkers currently used in the more common paediatric solid tumours, with a brief commentary on the most relevant less common predictive biomarkers. MYCN amplification is the most important genetic alteration in neuroblastoma prognosis, and the histological classification devised by Shimada in 1999 is still used in routine diagnosis. Moreover, a new subgrouping of unfavourable histology neuroblastoma enables immunohistochemical characterisation of tumours with markedly different genetic features and prognosis. The predominant histology and commonly observed cytogenetic abnormalities are recognised outcome predictors in Wilms tumour. Evaluation for anaplasia, which is tightly associated with TP53 gene mutations and poor outcomes, is central in both the International Society of Paediatric Oncology and the Children's Oncology Group approaches to disease classification. Characterisation of distinct genotype-phenotype subclasses and critical mutations has expanded overall understanding of hepatoblastoma outcomes. The C1 subclass hepatoblastoma and CTNNB1 mutations are associated with good prognosis. In contrast, the C2 subclass, NFE2L2 mutations, TERT promoter mutations and high expression of oncofetal proteins and stem cell markers are associated with poor outcomes. Risk stratification in sarcomas is highly variable depending on the entity. The prognosis of rhabdomyosarcoma, for example, primarily depends on histological and molecular characteristics. Advances in our understanding of clinically significant biomarkers will translate into more precise diagnoses, improved risk stratification and more effective and less toxic treatment in this challenging group of patients.

Spindle Cell Tumors of the Sinonasal Tract: A Diagnostic Update with Focus on Ancillary Workup

Spindle cell neoplasms arising in the head and neck may be challenging to recognize due to their relative rarity. While underlying molecular alterations are increasingly elucidated, testing for these features may not be readily available. In most cases, combinations of key morphologic features and diagnostic immunohistochemical markers can be used to replace molecular diagnostics. Conversely, some molecular alterations and expression of their surrogate biomarkers are not specific for any one entity, and it is important to recognize these to avoid diagnostic pitfalls. In this review, we discuss both old and new spindle cell tumors of the sinonasal tract, with an emphasis on histologic features and clinically relevant immunohistochemical markers serving as surrogate markers for underlying genomic alterations.

Pediatric spindle cell/sclerosing rhabdomyosarcoma with FUS-TFCP2 fusion: a case report and literature review

Background

FUS-TFCP2 gene fusion is a recently identified and highly distinct molecular subtype of spindle cell/sclerosing rhabdomyosarcoma (RMS), with fewer than 40 cases being reported to date. Due to its low incidence, clinical studies on this subtype are limited. Here, we report a new case of this rare entity to describe and summarize its unique clinical characteristics and treatment process, aiming to emphasize the importance of molecular testing for spindle cell/sclerosing RMS and increase the understanding of this subtype. By summarizing and comparing with previous reports on RMS with the EWSR1/FUS-TFCP2 fusion mutation, we hope to make some new hints for its management.

Case Description

In this report, we describe a rare case of spindle cell/sclerosing RMS in a 13-year-old boy, who had a massive destructive lesion involving the mandible. Next-generation sequencing of tumor tissue revealing a FUS-TFCP2 fusion. The tumor was extremely aggressive and showed resistance to polychemotherapy, after 4 cycles of multi drug combined chemotherapy, the primary tumor still continued to grow, and suspicious chest metastasis occurred. Even after aggressive total resection of the primary tumor and postoperative chemotherapy, systemic metastasis to the vertebra and chest could not be prevented yet, ultimately with a fatal outcome within 6 months. We additionally summarize 37 cases of RMS with the EWSR1/FUS-TFCP2 fusion mutation reported in the literature. This subtype was found to be almost exclusively primary in bone and histologically showed a common origin of epithelium and muscle. The high aggressiveness made the conventional standard chemoradiotherapy ineffective. Because most tumors of this subtype express ALK protein, ALK inhibitors seem to be a new target for its therapy.

Conclusions

Spindle cell/sclerosing RMS with FUS-TFCP2 fusion has its unique clinical characteristics and progression. It shows a marked skeletal predilection and an aggressive clinical course, typically resistant to traditional standard treatments for RMS. Therefore, molecular detection is crucial in managing this subtype. Once the diagnosis is clear, a more aggressive treatment plan is needed. In addition, almost all cases were found to have a positive expression of ALK. So ALK inhibitors can be a choice of targeted therapy.

Emerging mesenchymal tumour types and biases in the era of ubiquitous sequencing

New tumour types are being described at increasing frequency, and most new tumour types are now identified via retrospective review of next-generation sequencing data. This contrasts with the traditional, morphology-based method of identifying new tumour types, and while the sequencing-based approach has accelerated progress in the field, it has also introduced novel and under-recognised biases. Here, we discuss tumour types identified based on morphology, including superficial CD34-positive fibroblastic tumour, pseudoendocrine sarcoma and cutaneous clear cell tumour with melanocytic differentiation and ACTIN::MITF fusion. We also describe tumour types identified primarily by next-generation sequencing, including epithelioid and spindle cell rhabdomyosarcoma, round cell neoplasms with EWSR1::PATZ1 fusion, cutaneous melanocytic tumour with CRTC1::TRIM11 fusion, clear cell tumour with melanocytic differentiation and MITF::CREM fusion and GLI1-altered mesenchymal neoplasms, including nested glomoid neoplasm.

Elucidating dynamic cell lineages and gene networks in time-course single cell differentiation

Single cell RNA sequencing (scRNA-seq) technologies provide researchers with an unprecedented opportunity to exploit cell heterogeneity. For example, the sequenced cells belong to various cell lineages, which may have different cell fates in stem and progenitor cells. Those cells may differentiate into various mature cell types in a cell differentiation process. To trace the behavior of cell differentiation, researchers reconstruct cell lineages and predict cell fates by ordering cells chronologically into a trajectory with a pseudo-time. However, in scRNA-seq experiments, there are no cell-to-cell correspondences along with the time to reconstruct the cell lineages, which creates a significant challenge for cell lineage tracing and cell fate prediction. Therefore, methods that can accurately reconstruct the dynamic cell lineages and predict cell fates are highly desirable. In this article, we develop an innovative machine-learning framework called Cell Smoothing Transformation (CellST) to elucidate the dynamic cell fate paths and construct gene networks in cell differentiation processes. Unlike the existing methods that construct one single bulk cell trajectory, CellST builds cell trajectories and tracks behaviors for each individual cell. Additionally, CellST can predict cell fates even for less frequent cell types. Based on the individual cell fate trajectories, CellST can further construct dynamic gene networks to model gene-gene relationships along the cell differentiation process and discover critical genes that potentially regulate cells into various mature cell types.

Fusion-driven Spindle Cell Rhabdomyosarcomas of Bone and Soft Tissue: A Clinicopathologic and Molecular Genetic Study of 25 Cases

The evolving classification of rhabdomyosarcoma (RMS) now includes spindle cell RMS (SRMS). Bone/soft tissue SRMS often harbor TFCP2, or less often MEIS1 rearrangements. We studied 25 fusion-driven SRMS involving bone (n = 19) and soft tissue (n = 6). Osseous SRMS occurred in 13 women and 6 men (median age: 41 years) and involved the pelvis (5), sacrum (2), spine (4), maxilla (4), mandible (1), skull (1), and femur (2). Follow-up (median: 5 months) demonstrated local recurrence in 2/16 and distant metastases in 8/17 patients (median time to metastasis: 1 month). Eight patients died of disease; 9 were alive with disease. Soft tissue SRMS occurred in 4 men and 2 women (median: 50 years). Follow-up (median: 10 months) revealed distant metastasis at diagnosis (1), alive with unresected tumor (1), and no evidence of disease (4). Next-generation sequencing demonstrated FUS::TFCP2 (12), EWSR1::TFCP2 (3) and MEIS1::NCOA2 (2); FISH identified EWSR1 (2) rearrangements. Most TFCP2-rearranged SRMS (13/17) showed spindled/epithelioid morphology, rarely with rhabdomyoblasts. The bone tumors were diffusely desmin and MyoD1 positive with limited myogenin; 10/13 were ALK -positive and 6/15 were keratin positive. Soft tissue SRMS harbored EWSR1::TFCP2, MEIS1::NCOA2, ZFP64::NCOA2, MEIS1::FOXO1, TCF12::VGLL3 and DCTN1::ALK, and displayed spindled/epithelioid, leiomyomatous, and myxofibrosarcoma-like morphologies. Immunohistochemistry (IHC) was positive for MyoD1 (6/6), focal desmin (5/6), myogenin (3/6), and keratin (1/6). We conclude that TFCP2-rearranged SRMS of bone and soft tissue show consistent morphologic and IHC features, likely representing a distinct subset of RMS. Non-TFCP2 fusion-positive SRMS could represent a single RMS subset, multiple subtypes of RMS, or "fusion-defined" sarcomas with rhabdomyoblastic differentiation.

Loss of Chromosome 3q Is a Prognostic Marker in Fusion-Negative Rhabdomyosarcoma

PURPOSE

Soft tissue sarcomas (STS) are rare mesenchymal neoplasms that frequently show complex chromosomal aberrations such as amplifications or deletions of DNA sequences or even whole chromosomes. We recently found that gain of chromosome (chr) 8 is associated with worse overall survival (OS) in STS as a group. We therefore aimed to investigate the overall copy number profile of rhabdomyosarcoma (RMS) to evaluate for prognostic signatures.

METHODS

Fluorescence in situ hybridization (FISH) testing was performed on a cohort of STS to assess for chr8 gain. Copy number variation (CNV) data from the National Cancer Institute were analyzed to assess for prognostically significant CNV aberrations in FOXO1 fusion-negative (FN)- versus fusion-positive (FP)-RMS. FISH testing was performed on a cohort of FN-RMS to assess for chr3q loss and correlate with outcomes.

RESULTS

Chr8 gain is a highly prevalent CNV in embryonal RMS and shows slightly improved prognosis. Meanwhile, loss of chr3q was associated with worse outcome in FN-RMS compared with FP-RMS.

CONCLUSION

The pathogenesis of STS including FN-RMS remains poorly understood, emphasizing the need for new therapeutic advances and adequate risk stratification. Our data demonstrate that loss of chr3q is associated with poor OS in FN-RMS, supporting it as an important tool for risk stratification.

Intraosseous Spindle Cell Rhabdomyosarcoma with MEIS1::NCOA2 Fusion - Case Report with Substantial Clinical Follow-up and Review of the Literature

Spindle cell/sclerosing rhabdomyosarcoma (SSRMS) is a clinicopathologically and molecularly heterogeneous disease. Gene fusions have been identified in intraosseous SSRMS, consisting predominantly of EWSR1/FUS::TFCP2 and MEIS1::NCOA2. The former often follow an aggressive clinical course; there is limited clinical follow-up available for the latter. We report here a new case of the very rare intraosseous SSRMS with MEIS1::NCOA2 gene fusion and include the detailed treatment course and 52 months of clinical follow-up. SSRMS with MEIS1::NCOA2 gene fusion appears biologically distinct from other intraosseous SSRMS, following a course characterized by local recurrence with rare reports of metastasis to date.

Biphenotypic Sinonasal Sarcoma with a Novel PAX7::PPARGC1 Fusion: Expanding the Spectrum of Gene Fusions Beyond the PAX3 Gene

Biphenotypic sinonasal sarcoma (BSNS) is a rare low-grade malignancy occurring in the sinonasal tract that is characterized by dual neural and myogenic differentiation. Rearrangements involving the PAX3 gene, usually with MAML3, are a hallmark of this tumor type and their identification are useful for diagnosis. Rarely, a MAML3 rearrangement without associated PAX3 rearrangement has been described. Other gene fusions have not been previously reported. Herein, we report a 22 year-old woman with a BSNS harboring a novel gene fusion involving the PAX7 gene (specifically PAX7::PPARGC1A), which is a paralogue of PAX3. The histologic features of the tumor were typical with two exceptions: a lack of entrapment of surface respiratory mucosa and no hemangiopericytoma-like vasculature. Immunophenotypically, the tumor was notably negative for smooth muscle actin, which is usually positive in BSNS. However, the classic S100 protein-positive, SOX10-negative staining pattern was present. In addition, the tumor was positive for desmin and MyoD1 but negative for myogenin, a pattern that is common among BSNS with variant fusions. Awareness of the possibility of PAX7 gene fusions in BSNS is important as it may aid in the diagnosis of PAX3 fusion negative tumors.

Spindle Cell Rhabdomyosarcoma of the Inguinal Region Mimicking a Complicated Hernia in the Adult-An Unexpected Finding

Rhabdomyosarcoma is a rare tumor that is diagnosed mostly in children and adolescents, rarely in adults, representing 2-5% of all soft tissue sarcomas. It has four subtypes that are recognized: embryonal (50%), alveolar (20%), pleomorphic (20%), and spindle cell/sclerosing (10%). The diagnosis of rhabdomyosarcoma is based on the histological detection of rhabdomyoblasts and the expression of muscle-related biomarkers. Spindle cell/sclerosing rhabdomyosarcoma consists morphologically of fusiform cells with vesicular chromatin arranged in a storiform pattern or long fascicles, with occasional rhabdomyoblasts. Also, dense, collagenous, sclerotic stroma may be seen more commonly in adults. We present a rare case of an adult who presented to the hospital with a tumor in the left inguinal area, was first diagnosed with a left strangulated inguinal hernia and was operated on as an emergency, although the diagnosis was ultimately a spindle cell rhabdomyosarcoma of the inguinal region.

[Special mesenchymal neoplasms of the head and neck: Update from the 2022 WHO]

Similar to the approach adopted in the classification of tumors in other organs, a new feature of the current Word Health Organization (WHO) classification of the head and neck tumors is the exclusion of soft tissue tumors from single organs and their inclusion in a separate chapter devoted to them. This applies to tumors that are principally ubiquitous but show a predilection for the head and neck sites. The only exception to this rule represents those entities that are almost restricted to a specific head and neck site/organ (such as nasopharyngeal angiofibroma, sinonasal glomangiopericytoma, and biphenotypic sinonasal sarcoma), which remain in their respective organ chapters. Included among soft tissue tumors are some old but still underrecognized entities, such as phosphaturic mesenchymal tumors, and newly defined entities, such as GLI1-altered tumors. The aim of including these entities is to enhance recognition of these uncommon but likely under-recognized entities to better characterize them in the future. This review summarizes the main features of these rare entities and discusses their differential diagnoses.

Extremity Rhabdomyosarcoma-An Integrated Clinicopathologic and Genomic Study to Improve Risk Stratification

PURPOSE

Extremity rhabdomyosarcoma (RMS) is associated with a very poor outcome compared with other sites, mainly because of its high incidence of alveolar histology and regional lymph node involvement. To better define prognostic markers in this clinical subset, we investigated our experience of 61 patients with extremity RMS treated at our tertiary cancer center for the past 2 decades.

PATIENTS AND METHODS

The patients had a median age of 8 years at diagnosis, equal gender distribution, and two-thirds occurred in the lower extremity. Most (85%) patients had FOXO1 fusion-positive alveolar RMS (ARMS), with 70% having a PAX3::FOXO1 transcript. Remaining were seven patients with fusion-negative embryonal RMS (ERMS) and two with MYOD1-mutant spindle cell/sclerosing RMS (SRMS). In 40% of the patients, material was available for DNA-based targeted sequencing using MSK-IMPACT cancer gene panel.

RESULTS

One-third of patients presented with localized disease at diagnosis while the remaining had regional nodal (18%) or distant metastases (51%). Metastatic disease, high-risk group, and age 10 years or older significantly affected the overall survival (OS; hazard ratio [HR], 2.68 [P = .004], 2.78 [P = .010] and 2.26 [P = .034], respectively). Although the presence of metastatic disease had a dismal impact on 5-year EFS and OS (19% and 29%, respectively), nodal involvement had a comparatively lower impact on 5-year EFS and 5-year OS (43% and 66%, respectively). PAX3::FOXO1 ARMS had worse prognosis and afflicted older children compared with PAX7::FOXO1 (HR = 3.45, P = .016). The most common events in the ARMS group included MED12 alterations, CDK4 amplifications, and CDKN2A deletions (8%-17%). The latter two abnormalities were mutually exclusive, enriched for acral and high-risk lesions, and correlated with poor outcome on OS (P = .02).

CONCLUSION

Our data provide rationale for considering the integration of molecular abnormalities to refine risk stratification in extremity RMS.

Rhabdomyosarcoma Arising in Inflammatory Rhabdomyoblastic Tumor: A Genetically Distinctive Subtype of Rhabdomyosarcoma

"Inflammatory rhabdomyoblastic tumor" (IRMT) is a recently coined name for a distinctive soft tissue neoplasm characterized by slow growth, a dense histiocytic infiltrate, scattered, bizarre-appearing tumor cells with morphologic and immunohistochemical evidence of skeletal muscle differentiation, a near-haploid karyotype with retained biparental disomy of chromosomes 5 and 22, and usually indolent behavior. There are 2 reports of rhabdomyosarcoma (RMS) arising in IRMT. We studied the clinicopathologic and cytogenomic features of 6 cases of IRMT with progression to RMS. Tumors occurred in the extremities of 5 men and 1 woman (median patient age, 50 years; median tumor size, 6.5 cm). Clinical follow-up (6 patients: median, 11 months; range 4-163 months) documented local recurrence and distant metastases in 1 and 5 of 6 patients, respectively. Therapy included complete surgical resection (4 patients) and adjuvant/neoadjuvant chemo/radiotherapy (6 patients). One patient died of disease, 4 were alive with metastatic disease, and one was without evidence of disease. All primary tumors contained conventional IRMT. Progression to RMS appeared as follows: (1) overgrowth of monomorphic rhabdomyoblasts with diminished histiocytes, (2) monomorphic spindle cell morphology with variably pleomorphic rhabdomyoblasts and low mitotic activity, or (3) morphologically undifferentiated spindle cell and epithelioid sarcoma. All but one were diffusely desmin-positive, with more limited MyoD1/myogenin expression. All RMS arising in IRMT, either primary or metastatic, demonstrated widespread loss of heterozygosity with retained heterozygosity of chromosomes 5 and 20, and all but one displayed additional gains and losses involving loci containing oncogenes/ tumor suppressor genes, most often CDKN2A and CDKN2B. RMS arising in IRMT have unique clinicopathologic and cytogenomic features, warranting classification as a distinct, potentially aggressive RMS subtype. It should be distinguished from other RMSs, particularly fusion-driven spindle cell RMS and pleomorphic RMS.

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.

Unusual case of inflammatory rhabdomyoblastic tumor in a pediatric patient

Inflammatory rhabdomyoblastic tumor (IRMT) is a rare, recently described skeletal muscle neoplasm of uncertain malignant potential. We report an unusual tumor in the right arm of a 5-year-old boy, which is the first case of a pediatric IRMT. Immunohistochemically, most cells in the tumor were positive for CD163 and CD68 staining. The neoplastic cells themselves showed a skeletal muscle phenotype with a diffuse expression of desmin and a focal expression of myoD1. Mitotic activity was low (1/10 HPF), and no necrosis was observed.

Epithelioid and spindle rhabdomyosarcoma with TFCP2 rearrangement in abdominal wall: a distinctive entity with poor prognosis

BACKGROUND

Epithelioid and spindle rhabdomyosarcoma (ES-RMS) with TFCP2 rearrangement is a recently discovered rare variant of rhabdomyosarcoma composed of epithelioid and spindle cells, because it shows extraordinarily adverse prognosis and is easily misdiagnosed as other epithelioid or spindle cell tumors.

METHODS

A rare case of ES-RMS with TFCP2 rearrangement was presented and English literatures in Pubmed online up to 01 July 2022 were gathered by two authors for a systematic review according to the inclusion and exclusion criteria.

CASE PRESENTATION/RESULTS

We report a case of ES-RMS in an early 30s-years-old female, the neoplastic cells are remarkably immunoreactive with CK(AE1/AE3), and partially with ALK protein. Unexpectedly, the tumor shows TFCP2 rearrangement with coexistence of increased copy numbers of EWSR1 and ROS1 gene and MET gene mutation. Besides, Next-generation sequencing for genetic mutational profiling revealed frequent MET exon14 mutations in chromosome 7, most of which are C > T nonsynonymous SNV, and exon42 of ROS1 in chromosome 6 showed frequent G > T mutation up to 57.54%. In addition, neither MyoD1 mutation nor gene fusions were detected. Moreover, the patient shows high tumor mutational burden (TMB) up to 14.11 counts/Mb. Finally, as many cases of ES-RMS including our case had local progression or metastasis, we find, similar to epithelioid rhabdomyosarcoma (median survival time is 10 month), ES-RMS shows a more aggressive behavior and adverse prognosis (median survival time is 17 month) than spindle cell/sclerosing rhabdomyosarcoma (median survival time is 65 month) according previous studies.

CONCLUSIONS

ES-RMS with TFCP2 rearrangement is a rare malignant tumor and easily confused with other epithelioid or spindle cell tumors, it may harbor additional gene alteration in addition to TFCP2 rearrangement, such as MET mutation, increased copy numbers of EWSR1 and ROS1 gene, high TMB. Most importantly, it may show very poor outcome with extensive metastasis.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

Biological Role and Clinical Implications of MYOD1L122R Mutation in Rhabdomyosarcoma

Major progress in recent decades has furthered our clinical and biological understanding of rhabdomyosarcoma (RMS) with improved stratification for treatment based on risk factors. Clinical risk factors alone were used to stratify patients for treatment in the European Pediatric Soft Tissue Sarcoma Study Group (EpSSG) RMS 2005 protocol. The current EpSSG overarching study for children and adults with frontline and relapsed rhabdomyosarcoma (FaR-RMS NCT04625907) includes FOXO1 fusion gene status in place of histology as a risk factor. Additional molecular features of significance have recently been recognized, including the MYOD1^L122R gene mutation. Here, we review biological information showing that MYOD1^L122R blocks cell differentiation and has a MYC-like activity that enhances tumorigenesis and is linked to an aggressive cellular phenotype. MYOD1^L122R mutations can be found together with mutations in other genes, such as PIK3CA, as potentially cooperating events. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, ten publications in the clinical literature involving 72 cases were reviewed. MYOD1^L122R mutation in RMS can occur in both adults and children and is frequent in sclerosing/spindle cell histology, although it is also significantly reported in a subset of embryonal RMS. MYOD1^L122R mutated tumors most frequently arise in the head and neck and extremities and are associated with poor outcome, raising the issue of how to use MYOD1^L122R in risk stratification and how to treat these patients most effectively.

A rare case of rhabdomyosarcoma identified in a VRAM flap after lower extremity reconstruction

Spindle cell sclerosing rhabdomyosarcoma (sc-RMS) is an extremely rare soft tissue tumor. We report an unusual case of sc-RMS in a 36-year-old patient whose tumor arose in a rectus abdominis muscle free flap that had been used for lower extremity reconstruction 18 years previously. After surgical excision of the tumor and immediate reconstruction, the patient has remained in remission and has full function of his lower extremity six months after diagnosis and treatment.

Predicting Molecular Subtype and Survival of Rhabdomyosarcoma Patients Using Deep Learning of H&E Images: A Report from the Children's Oncology Group

PURPOSE

Rhabdomyosarcoma (RMS) is an aggressive soft-tissue sarcoma, which primarily occurs in children and young adults. We previously reported specific genomic alterations in RMS, which strongly correlated with survival; however, predicting these mutations or high-risk disease at diagnosis remains a significant challenge. In this study, we utilized convolutional neural networks (CNN) to learn histologic features associated with driver mutations and outcome using hematoxylin and eosin (H&E) images of RMS.

EXPERIMENTAL DESIGN

Digital whole slide H&E images were collected from clinically annotated diagnostic tumor samples from 321 patients with RMS enrolled in Children's Oncology Group (COG) trials (1998-2017). Patches were extracted and fed into deep learning CNNs to learn features associated with mutations and relative event-free survival risk. The performance of the trained models was evaluated against independent test sample data (n = 136) or holdout test data.

RESULTS

The trained CNN could accurately classify alveolar RMS, a high-risk subtype associated with PAX3/7-FOXO1 fusion genes, with an ROC of 0.85 on an independent test dataset. CNN models trained on mutationally-annotated samples identified tumors with RAS pathway with a ROC of 0.67, and high-risk mutations in MYOD1 or TP53 with a ROC of 0.97 and 0.63, respectively. Remarkably, CNN models were superior in predicting event-free and overall survival compared with current molecular-clinical risk stratification.

CONCLUSIONS

This study demonstrates that high-risk features, including those associated with certain mutations, can be readily identified at diagnosis using deep learning. CNNs are a powerful tool for diagnostic and prognostic prediction of rhabdomyosarcoma, which will be tested in prospective COG clinical trials.

Case report: Clinical features and prognosis of two Infants with rhabdomyosarcoma of the tongue

Background

Rhabdomyosarcoma (RMS) is the most common soft tissue tumor in children, and its most common pathological types include embryonal RMS and alveolar RMS. In contrast, spindle cell RMS (SRMS) is a rare type. Moreover, the tongue is a rare primary site of RMS, and infancy is a rare age at onset.

Case presentation

Two infants were diagnosed with lingual RMS at 3 and 5 months after birth, respectively, and were admitted to Beijing Children's Hospital. The pathological type in both cases was SRMS. Both were classified as low-risk and were treated with surgery and chemotherapy. Case 1 was in complete remission at the latest follow-up, and Case 2 had a relapse 10 months after stopping chemotherapy, achieving complete remission after the multimodal treatment of chemotherapy, surgery, and radiotherapy. The venous blood gene test of the two infants did not indicate a pathogenic mutation or a possible pathogenic mutation related to RMS. In Case 1, variants of the CDK4 and BRCA1 genes, both with unknown significance and a possible relation to RMS, were detected. In Case 2, three gene variants of unknown significance that were possibly associated with RMS-TRIP13, APC, and RAD54L-were identified.

Conclusion

Lingual RMS in infants is rare. Its clinical manifestations lack specificity, and early recognition is complex. The success and timing of local treatment are important prognostic factors. Genetic testing may be helpful for the early detection of tumor susceptibility and the estimation of prognosis.

Shedding a Light on the Challenges of Adolescents and Young Adults with Rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a typical tumour of childhood but can occur at any age. Several studies have reported that adolescent and young adult (AYA) patients with RMS have poorer survival than do younger patients. This review discusses the specific challenges in AYA patients with pediatric-type RMS, exploring possible underlying factors which may influence different outcomes. Reasons for AYA survival gap are likely multifactorial, and might be related to differences in tumor biology and intrinsic aggressiveness, or differences in clinical management (that could include patient referral patterns, time to diagnosis, enrolment into clinical trials, the adequacy and intensity of treatment), as well as patient factors (including physiology and comorbidity that may influence treatment tolerability, drug pharmacokinetics and efficacy). However, improved survival has been reported in the most recent studies for AYA patients treated on pediatric RMS protocols. Different strategies may help to further improve outcome, such as supporting trans-age academic societies and national/international collaborations; developing specific clinical trials without upper age limit; defining integrated and comprehensive approach to AYA patients, including the genomic aspects; establishing multidisciplinary tumor boards with involvement of both pediatric and adult oncologists to discuss all pediatric-type RMS patients; developing dedicated projects with specific treatment recommendations and registry/database.

Infantile Fibrosarcoma and Other Spindle Cell Neoplasms of Infancy. A Review of Morphologically Overlapping yet Molecularly Distinctive Entities

BACKGROUND

Regardless of age at presentation, many soft tissue neoplasms have overlapping histopathologic and immunophenotypic features to serve as a diagnostic challenge.

CASE REPORT

We reported a case of a spindle cell neoplasm in an infant, which was initially considered a vascular anomaly clinically and an eventual biopsy revealed marked inflammation with a spindle cell component that was resolved as an infantile fibrosarcoma with an ETV6 break-apart.

CONCLUSION

The context of this case lead to a further consideration of various other spindle cell neoplasms arising predominantly in the soft tissues during the infancy period as defined by the first two years of age. Though sharing similar morphologic features, these tumors can be categorized into several molecular genetic groups, which have provided both diagnostic and pathogenetic insights as well as treatment options in some cases.

Cytomorphology of spindle cell/sclerosing rhabdomyosarcoma, including MYOD1 (LI22R) mutation result

Spindle cell/sclerosing rhabdomyosarcoma (RMS), characterized by MYOD1 (L122R) mutation in a subset of cases is a newly described subtype of RMS. Presently, there is no documentation of cytomorphological features, especially of sclerosing RMS. Case 1: A 24-year-old male presented with pain and swelling in his wrist for a one-year duration. MRI revealed a well-defined soft tissue lesion measuring 5.3 cm, encasing the lower end of the ulna. Fine-needle aspiration cytology (FNAC) smears revealed clusters of tumor cells with round to oval to spindle-shaped nuclei, scant to moderate amount of cytoplasm with the wisps of the metachromatic stroma. Histopathological examination revealed a malignant tumor comprising cells with polygonal to spindle-shaped nuclei, arranged in a sclerotic stroma. Immunohistochemically, the tumor cells were positive for desmin, myogenin, and MYOD1. A diagnosis of sclerosing RMS was offered. Furthermore, the tumor revealed MYOD1 (L122R) mutation. Case 2: A 43-year-old male presented with a 4-month history of "nasal stuffiness" and pressure. Imaging revealed a poorly defined infiltrative lesion in his nasal cavity. FNAC smears revealed loose and tightly cohesive clusters of malignant cells with oval to spindle-shaped nuclei, a moderate amount of ill-defined bluish to finely vacuolated cytoplasm, and focal streak artifact with interspersed stromal fragments. Histopathological examination revealed a malignant tumor composed of oval to spindle-shaped nuclei, embedded in a variably hyalinized stroma. Immunohistochemically, the tumor cells were positive for desmin, and myogenin. Diagnosis of spindle cell/sclerosing RMS was offered. The present study constitutes one of the first documentation of cytomorphological features of two rare cases of spindle cell/sclerosing RMS. The differential diagnoses and treatment-related implications are presented.

Recurrent VGLL3 fusions define a distinctive subset of spindle cell rhabdomyosarcoma with an indolent clinical course and striking predilection for the head and neck

The mammalian Vestigial-like (VGLL) transcriptional cofactor family of proteins VGLL1-4 has recently emerged as an important player in the tumorigenesis of diverse neoplasms. The role of VGLL3 in soft tissue tumors is exemplified by its amplification in myxoinflammatory fibroblastic sarcoma and its rearrangement (fused to CHD7, CHD9, or MAMLD1) in hybrid schwannoma-perineurioma. This study characterizes a distinctive low-grade myogenic neoplasm with a striking predilection for the head and neck, characterized by VGLL3 fusions. The study includes five males and one female patient, aged 30-71 years (median, 56). Three tumors originated in the tongue, with one case each in the nasopharynx, oral cavity, and oropharynx. The VGLL3 fusion partners included TCF12 (n = 3), EP300 (n = 2), and PPARGC1A (n = 1). The tumor size range was 0.8-1.6 cm (all, but one, was <1 cm). Histologically, all tumors displayed bland spindle to ovoid cells arranged into vague fascicular and diffuse patterns. Mitotic activity ranged from 1 to 7 per 10 HPFs. Five tumors were muscle-centered and infiltrative, and one was centered beneath nasopharyngeal mucosa. Immunohistochemistry revealed consistent expression of desmin (diffuse in four and patchy in two cases) associated with patchy smooth muscle actin expression (4/6), and focal reactivity for myogenin (5/6) and myoD1 (1/3). All patients were managed surgically; one patient each received adjuvant radio- or chemotherapy. Three patients with follow-up were without disease at 8, 19, and 60 months and one was alive with unknown disease status at 24 months. All VGLL3 fusions were in-frame and involved exon 2, fused with either TCF12 exon 16, EP300 exon 31, or PPARGC1A exon 5, respectively. This series characterizes a distinctive subset of spindle cell rhabdomyosarcoma (RMS) with a predilection for the head and neck in adults, defined by VGLL3 fusions, likely indolent behavior and limited rhabdomyoblastic differentiation. Further delineation of this entity and differentiation from more aggressive molecular subtypes of spindle cell RMS is mandatory to define the most appropriate therapeutic strategy and avoid overtreatment.

Rhabdomyosarcoma With FUS::TFCP2 Fusion in the Scalp: A Rare Case Report Depicting Round and Spindle cell Morphology

Rhabdomyosarcoma (RMS) is a nonepithelial malignant tumor that differentiates into immature skeletal muscle. It is currently classified into 4 main subtypes according to the WHO classification. However, based on clinicopathological and molecular findings, there has been an increasing number of cases that do not fit into any of these subtypes. TFCP2-rearranged RMS is a rare tumor with characteristic clinicopathological findings including a preference for the craniofacial bones, a spindle and epithelioid histomorphology, and positive immunohistochemistry for epithelial markers, ALK, and myogenic markers. In this report, we describe a rare case of RMS with FUS::TFCP2 fusion in the scalp of a 58-year-old man. Histologically, the tumor showed a biphasic pattern, with solid proliferation of round cells in the superficial areas and of spindle cells in the deep areas. Immunohistochemically, tumor cells were positive for pan keratin, myogenic markers (desmin, MYOD1, and myogenin), and ALK. Additionally, fluorescence in situ hybridization using a break-apart FUS probe revealed FUS rearrangement. RMS with FUS::TFCP2 fusion was suspected, and the fusion gene was finally confirmed by target fusion sequencing. We believe that detailed histological, immunohistochemical, and genetic findings were important for the diagnosis. The unique traits of this tumor were the biphasic histological appearance consisting of round and spindle cells and development in the skin and soft tissue.

ZFP64::NCOA3 gene fusion defines a novel subset of spindle cell rhabdomyosarcoma

Spindle cell rhabdomyosarcoma represents a rare neoplasm characterized by monomorphic spindle cells with a fascicular architecture and variable skeletal muscle differentiation. Following incidental identification of a ZFP64::NCOA3 gene fusion in an unclassified spindle cell sarcoma resembling adult-type fibrosarcoma, we performed a retrospective archival review and identified four additional cases with a similar histology and identical gene fusion. All tumors arose in adult males (28-71 years). The neoplasms were found in the deep soft tissues, two were gluteal, and one each arose in the thigh, abdominal wall, and chest wall. Morphologically, the tumors were characterized by spindle cells with a distinctive herringbone pattern and variable collagenous to myxoid stroma. The nuclei were relatively monomorphic with variable mitotic activity. Three tumors had immunoreactivity for MyoD1, and four contained variable expression of desmin and smooth muscle actin. All cases tested for myogenin, CD34, S100, pankeratin, and epithelial membrane antigen were negative. Targeted RNA sequencing revealed a ZFP64::NCOA3 fusion product in all five tumors. Three patients developed distant metastases, and two ultimately succumbed to their disease within 2 years of initial diagnosis. This study suggests ZFP64::NCOA3 fusions define a novel subtype of rhabdomyosarcoma with a spindle cell morphology and aggressive clinical behavior. The potential for morphologic and immunohistochemical overlap with several other sarcoma types underscores the value of molecular testing as a diagnostic adjunct to ensure accurate classification and management of these neoplasms.

Molecular profile of head and neck rhabdomyosarcomas: A systematic review and meta-analysis

OBJECTIVE

This systematic review aimed to identify the molecular alterations of head and neck rhabdomyosarcomas (HNRMS) and their prognostic values.

STUDY DESIGN

An electronic search was performed using PubMed, Embase, Scopus, and Web of Science with a designed search strategy. Inclusion criteria comprised cases of primary HNRMS with an established histopathological diagnosis and molecular analysis. Forty-nine studies were included and were appraised for methodological quality using the Joanna Briggs Institute Critical Appraisal tools. Five studies were selected for meta-analysis.

RESULTS

HNRMS predominantly affects pediatric patients (44.4%), and the parameningeal region (57.7%) is the most common location. The alveolar variant (43.2%) predominates over the embryonal and spindle cell/sclerosing types, followed by the epithelioid and pleomorphic variants. PAX-FOXO1 fusion was observed in 103 cases of alveolar RMS (79.8%). MYOD1 mutation was found in 39 cases of sclerosing/spindle cell RMS (53.4%). FUS/EWSR1-TFCP2 gene fusions were identified in 21 cases of RMS with epithelioid and spindle cell morphologies (95.5%). The 5-year overall survival rate of patients was 61.3%, and MYOD1 mutation correlated with significantly higher mortality.

CONCLUSION

The genotypic profile of histologic variants of HNRMS is widely variable, and MYOD1 mutation could be a potential prognostic factor, but more studies are required to establish this.

Embryonal Rhabdomyosarcoma of the Uterine Cervix: A Clinicopathologic Study of 94 Cases Emphasizing Issues in Differential Diagnosis Staging, and Prognostic Factors

Embryonal rhabdomyosarcoma of the uterine cervix (cERMS) is rare and frequently associated with DICER1 mutations. We report 94 tumors that arose in patients aged 7 to 59 (median=23) years and presented with vaginal bleeding (52), protruding vaginal mass (17), cervical polyp (8), or expelled tumor fragments per vagina (5). Nine had DICER1 syndrome, 8 of whom had other syndromic manifestations including ovarian Sertoli-Leydig cell tumor (7), multinodular goiter (3), pleuropulmonary blastoma (2), pineoblastoma (1), and osteosarcoma (1). Syndromic patients were younger than nonsyndromic patients (16 vs. 24 y). Tumor size ranged from 2 to 24 (median=4.5) cm. Ninety-two tumors were polypoid, most being grape-like (77 of 92). They were characterized by aggregates of primitive cells, almost always exhibiting a cambium layer, within a variably myxoedematous stroma and were hypocellular (63), moderately cellular (22), or hypercellular (9). Entrapped glands, typically scant, were present in 84 tumors. Primitive hyperchromatic ovoid to spindled cells with minimal cytoplasm predominated but differentiated rhabdomyoblasts with abundant eosinophilic cytoplasm (having cross-striations in 30) were seen in 83 tumors; they were often sparse but predominated in three. Nine tumors showed areas of intersecting fascicles and 4 zones with densely cellular (solid) growth. Cartilage was present in 38. Anaplasia was seen in 15 tumors, as was necrosis. Mitotic activity ranged from 1 to 58/10 high-power fields (median=8). The varied microscopic features resulted in a spectrum of differential diagnostic considerations, mainly typical and cellular forms of fibroepithelial polyps, Mullerian adenosarcoma, and other sarcomas. Follow-up was available for 79 patients ranging from 6 to 492 (median=90) months. Treatment information was available in 62 and included polypectomy in 6 patients (2 also received chemotherapy), limited resection in 26 (14 also received chemotherapy), hysterectomy in 29 (15 with adjuvant chemotherapy), and biopsies only in 1 (with chemotherapy). Staging was possible in 56 tumors; according to the "uterine sarcoma" system (tumor size and extent) they were: stage I (10/56; could not be further subclassified as size not available), IA (22/56), IB (18/56), IIA (2/56), IIB 3/56), IIIC (1/56). According to the "adenosarcoma" system (depth of invasion and extent) they were: stage IA (26/56), IB (14/56), IC (10/56), IIA (2/56), IIB (3/56), IIIC (1/56). Eight patients had local recurrence following incomplete excision (10%). Eleven of 79 patients had extrauterine recurrences (14%) and 9 died of disease (11%). Older age was associated with extrauterine recurrence (median 44 vs. 22; P=0.002) and decreased disease-specific survival (median 44 vs. 22; P=0.02). For patients with tumors initially confined to the cervix, the adenosarcoma staging system was superior to the uterine sarcoma staging system for predicting survival (P=0.02). Three patients with DICER1 syndrome who underwent fertility-preserving surgery developed a second primary cERMS 7, 7, and 12 years after their primary tumor. All 9 patients with DICER1 syndrome had tumors confined to the cervix and none died of disease. This study highlights the intriguing clinical aspects of cERMS including its long-known tendency to occur in the young but also more recently appreciated association with DICER1 syndrome. Establishing the diagnosis may still be difficult because of the hazard of sampling a neoplasm which in areas may appear remarkably bland and also because of its potential confusion with other neoplasms. This study indicates that this tumor has a good prognosis at this site and in selected cases a conservative surgical approach is a realistic consideration.

Exon skipping in genes encoding lineage-defining myogenic transcription factors in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a childhood sarcoma composed of myoblast-like cells, which suggests a defect in terminal skeletal muscle differentiation. To explore potential defects in the differentiation program, we searched for mRNA splicing variants in genes encoding transcription factors driving skeletal muscle lineage commitment and differentiation. We studied two RMS cases and identified altered splicing resulting in "skipping" the second of three exons in MYOD1. RNA-Seq data from 42 tumors and additional RMS cell lines revealed exon 2 skipping in both MYOD1 and MYF5 but not in MYF6 or MYOG. Complementary molecular analysis of MYOD1 mRNA found evidence for exon skipping in 5 additional RMS cases. Functional studies showed that so-called MYODΔEx2 protein failed to robustly induce muscle-specific genes, and its ectopic expression conferred a selective advantage in cultured fibroblasts and an RMS xenograft. In summary, we present previously unrecognized exon skipping within MYOD1 and MYF5 in RMS, and we propose that alternative splicing can represent a mechanism to alter the function of these two transcription factors in RMS.

Single-cell analysis and functional characterization uncover the stem cell hierarchies and developmental origins of rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a common childhood cancer that shares features with developing skeletal muscle. Yet, the conservation of cellular hierarchy with human muscle development and the identification of molecularly defined tumor-propagating cells has not been reported. Using single-cell RNA-sequencing, DNA-barcode cell fate mapping and functional stem cell assays, we uncovered shared tumor cell hierarchies in RMS and human muscle development. We also identified common developmental stages at which tumor cells become arrested. Fusion-negative RMS cells resemble early myogenic cells found in embryonic and fetal development, while fusion-positive RMS cells express a highly specific gene program found in muscle cells transiting from embryonic to fetal development at 7-7.75 weeks of age. Fusion-positive RMS cells also have neural pathway-enriched states, suggesting less-rigid adherence to muscle-lineage hierarchies. Finally, we identified a molecularly defined tumor-propagating subpopulation in fusion-negative RMS that shares remarkable similarity to bi-potent, muscle mesenchyme progenitors that can make both muscle and osteogenic cells.

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.

The Molecular Biology of Soft Tissue Sarcomas: Current Knowledge and Future Perspectives

Simple Summary

Over the past 20 years, significant advances in the field of genetics and molecular biology have led to the dismantlement of multiple subtypes of sarcomas. As a result, molecular approaches nowadays play a critical role in the diagnosis, prognostic classification, and therapeutic management of numerous mesenchymal tumor subtypes. This review of the current literature illustrates the main uses of molecular biology in the field of soft tissue sarcomas and the future challenges that remain to be addressed.

Abstract

Soft tissue sarcomas are malignant tumors of mesenchymal origin, encompassing a large spectrum of entities that were historically classified according to their histological characteristics. Over the last decades, molecular biology has allowed a better characterization of these tumors, leading to the incorporation of multiple molecular features in the latest classification of sarcomas as well as to molecularly-guided therapeutic strategies. This review discusses the main uses of molecular biology in current practice for the diagnosis and treatment of soft tissue sarcomas, in addition to perspectives for this rapidly evolving field of research.

Optimizing Rhabdomyosarcoma Treatment in Adolescents and Young Adults

Rhabdomyosarcoma (RMS) is the most common form of soft tissue sarcoma in children, but can also develop in adolescents and young adults (AYA). The mainstay of treatment is multi-agent chemotherapy, ideally with concomitant local treatment, including surgical resection and/or radiation therapy. Although most treatment decisions for RMS in AYA are based on scientific evidence accumulated through clinical studies of pediatric RMS, treatment outcomes are significantly inferior in AYA patients than in children. Factors responsible for the significantly poor outcomes in AYA are tumor biology, the physiology specific to the age group concerned, refractoriness to multimodal treatments, and various psychosocial and medical care issues. The present review aims to examine the various issues involved in the treatment and care of AYA patients with RMS, discuss possible solutions, and provide an overview of the literature on the topic with several observations from the author's own experience. Clinical trials for RMS in AYA are the best way to develop an optimal treatment. However, a well-designed clinical trial requires a great deal of time and resources, especially when targeting such a rare population. Until clinical trials are designed and implemented, and their findings duly analyzed, we must provide the best possible practice for RMS treatment in AYA patients based on our own expertise in manipulating the dosage schedules of various chemotherapeutic agents and administering local treatments in a manner appropriate for each patient. Precision medicine based on state-of-the-art cancer genomics will also form an integral part of this personalized approach. In the current situation, the only way to realize such a holistic treatment approach is to integrate new developments and findings, such as gene-based diagnostics and treatments, with older, fundamental evidence that can be selectively applied to individual cases.

Spindle Cell/Sclerosing Rhabdomyosarcoma With PAX8::PPARG Fusion

The spindle cell/sclerosing subtype of rhabdomyosarcoma is classified based on genetic features into the three categories of MYOD1-mutated, gene fusion-driven, and a subset without a currently identified genetic driver event. The gene fusion-driven spindle cell/sclerosing rhabdomyosarcomas are heterogenous and characterized by increasing numbers of gene fusions, the most common gene partners being VGLL2, NCOA2, and TFCP2. Here we report a spindle cell/sclerosing rhabdomyosarcoma that arose in the orbit of a 4-year-old male. This tumor harbored a unique PAX8::PPARG fusion. PAX8::PPARG fusions have previously only been described in follicular thyroid carcinoma and follicular variant of papillary thyroid carcinoma. Our report adds to the growing number of gene fusions in spindle cell/sclerosing rhabdomyosarcomas.

Congenital spindle cell rhabdomyosarcoma: An international cooperative analysis

BACKGROUND

Spindle cell rhabdomyosarcoma (RMS) is a rare variant of RMS accounting for up to 10% of cases in infants. In older children and adults, spindle cell RMS is associated with MYOD1 mutations and a poor prognosis. In infants, it is associated with recurring fusions involving NCOA2 and VGLL2. Reports in the literature suggest a favorable prognosis for this subset, however, little is known about treatment and outcome data of infants with spindle cell RMS.

METHODS

Characteristics, treatment, and outcome of an international cohort of 40 patients aged ≤ 12 months with spindle cell RMS treated from 1997 to 2018 were evaluated.

RESULTS

Localized disease (LD) was diagnosed in 39 patients. The median age at diagnosis was 2.5 months (range 0-12 months). Expert pathologic review confirmed the diagnosis of spindle cell RMS in all patients. Among 26 tumors that had molecular evaluation, 13 had rearrangements of NCOA and/or VGLL. Multimodal treatment of infants with LD included conventional (age adjusted) chemotherapy (n = 37), resection (n = 31) and radiotherapy (RT) (n = 5, brachytherapy in 3). Complete remission was achieved in 37/39 patients. Progressive disease occurred in two infants, relapsed disease in three. Microscopically complete surgical resection was associated with five-year event-free survival (EFS) and overall survival (OS) of 100%. Two patients with tumors ≤ 5 cm were treated with microscopically complete resection only and were alive 1 and 4.2 years after diagnosis. The 5-year EFS and OS for infants with LD were 86% (±11; CI 95%) and 91% (±9; CI 95%), respectively. One patient had metastatic disease (NCOA fusion positive) with primary tumor in head and neck and brain metastases. This patient died despite chemotherapy and delayed resection of the primary tumor due to respiratory failure secondary to cytomegalovirus infection 1.2 years after diagnosis.

CONCLUSION

Infants with spindle cell RMS have an excellent prognosis. Multimodal treatment including microscopically complete resection of the tumor is strongly recommended.

Molecular Markers of Pediatric Solid Tumors—Diagnosis, Optimizing Treatments, and Determining Susceptibility: Current State and Future Directions

Advances in molecular technologies, from genomics and transcriptomics to epigenetics, are providing unprecedented insight into the molecular landscape of pediatric tumors. Multi-omics approaches provide an opportunity to identify a wide spectrum of molecular alterations that account for the initiation of the neoplastic process in children, response to treatment and disease progression. The detection of molecular markers is crucial to assist clinicians in accurate tumor diagnosis, risk stratification, disease subtyping, prediction of treatment response, and surveillance, allowing also for personalized cancer management. This review summarizes the most recent developments in genomics research and their relevance to the field of pediatric oncology with the aim of generating an overview of the most important, from the clinical perspective, molecular markers for pediatric solid tumors. We present an overview of the molecular markers selected based on therapeutic protocols, guidelines from international committees and scientific societies, and published data.

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.

Spindle cell/sclerosing rhabdomyosarcoma with DCTN1::ALK fusion: broadening the molecular spectrum with potential therapeutic implications

Spindle cell/sclerosing rbabdomyosarcoma (RMS) is a recently characterized variant of RMS with several distinct molecular subtypes. We describe an example occurring in the tongue of a 10-year-old boy with a novel DCTN1::ALK fusion. The tumor exhibited infiltrative growth and was comprised of fascicles and focally whorls of spindle cells with eosinophilic cytoplasm, in a collagenous or myxoid stroma. Moderate cytologic atypia, mitotic activity (2/10 HPFs), and perineural invasion were identified. The tumor cells expressed actin, desmin, MyoD1, myogenin, and ALK. An in-frame fusion between DCTN1 exon 26 and ALK exon 20 was detected by RNA sequencing, which was confirmed by split reads and supported by FISH studies. The tumor showed an indolent behavior with local recurrence 3 years after excision. This study broadens the molecular spectrum of spindle cell/sclerosing RMS and this molecular aberration may represent a potential therapeutic target for unresectable or disseminated disease.

Chromatin Mechanisms Driving Cancer

The change in cell state from normal to malignant is driven fundamentally by oncogenic mutations in cooperation with epigenetic alterations of chromatin. These alterations in chromatin can be a consequence of environmental stressors or germline and/or somatic mutations that directly alter the structure of chromatin machinery proteins, their levels, or their regulatory function. These changes can result in an inability of the cell to differentiate along a predefined lineage path, or drive a hyperactive, highly proliferative state with addiction to high levels of transcriptional output. We discuss how these genetic alterations hijack the chromatin machinery for the oncogenic process to reveal unique vulnerabilities and novel targets for cancer therapy.

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.

Functional impact and targetability of PI3KCA, GNAS, and PTEN mutations in a spindle cell rhabdomyosarcoma with MYOD1 L122R mutation

Spindle cell/sclerosing rhabdomyosarcoma (ssRMS) is a rare subtype of rhabdomyosarcoma, commonly harboring a gain-of-function L122R mutation in the muscle-specific master transcription factor MYOD1. MYOD1-mutated ssRMS is almost invariably fatal, and development of novel therapeutic approaches based on the biology of the disease is urgently needed. MYOD1 L122R affects the DNA-binding domain and is believed to confer MYC-like properties to MYOD1, driving oncogenesis. Moreover, the majority of the MYOD1-mutated ssRMS harbor additional alterations activating the PI3K/AKT pathway. It is postulated that the PI3K/AKT pathway cooperates with MYOD1 L122R. To address this biological entity, we established and characterized a new patient-derived ssRMS cell line OHSU-SARC001, harboring MYOD1 L122R as well as alterations in PTEN, PIK3CA, and GNAS. We explored the functional impact of these aberrations on oncogenic signaling with gain-of-function experiments in C2C12 murine muscle lineage cells. These data reveal that PIK3CA^I459_T462del, the novel PIK3CA variant discovered in this patient specimen, is a constitutively active kinase, albeit to a lesser extent than PI3KCA^E545K, a hotspot oncogenic mutation. Furthermore, we examined the effectiveness of molecularly targeted PI3K/AKT/mTOR and RAS/MAPK inhibitors to block oncogenic signaling and suppress the growth of OHSU-SARC001 cells. Dual PI3K/mTOR (LY3023414, bimiralisib) and AKT inhibitors (ipatasertib, afuresertib) induced dose-dependent reductions in cell growth. However, mTOR-selective inhibitors (everolimus, rapamycin) alone did not exert cytotoxic effects. The MEK1/2 inhibitor trametinib did not impact proliferation even at the highest doses tested. Our data suggest that molecularly targeted strategies may be effective in PI3K/AKT/mTOR-activated ssRMS. Taken together, these data highlight the importance of utilizing patient-derived models to assess molecularly targetable treatments and their potential as future treatment options.