Epithelioid sarcoma (EpS) is an ultra-rare malignant soft-tissue cancer mostly affecting adolescents and young adults. EpS often exhibits an unfavorable clinical course with fatal outcome in ∼50% of cases despite aggressive multimodal therapies combining surgery, chemotherapy, and irradiation. EpS is traditionally classified in a more common, less aggressive distal (classic) type and a rarer aggressive proximal type. Both subtypes are characterized by a loss of nuclear INI1 expression, most often following homozygous deletion of its encoding gene, SMARCB1—a core subunit of the SWI/SNF chromatin remodeling complex. In 2020, the EZH2 inhibitor tazemetostat was the first targeted therapy approved for EpS, raising new hopes. Still, the vast majority of patients did not benefit from this drug or relapsed rapidly. Further, other recent therapeutic modalities, including immunotherapy, are only effective in a fraction of patients. Thus, novel strategies, specifically targeted to EpS, are urgently needed. To accelerate translational research on EpS and eventually boost the discovery and development of new diagnostic tools and therapeutic options, a vibrant translational research community has formed in past years and held two international EpS digital expert meetings in 2021 and 2023. This review summarizes our current understanding of EpS from the translational research perspective and points to innovative research directions to address the most pressing questions in the field, as defined by expert consensus and patient advocacy groups.

10061 Background: Genomics precision medicine, deployed via tumor panel sequencing, now assists in deploying targeted therapies to cancer patients. Numerous clinical trials have investigated the utility and benefit of genomics precision medicine in multiple cancer indications. Current large-scale studies report actionability rates from ~35% to ~60%, although clinical benefit rates have been shown to be closer to 10%. While this has positively impacted patients in need, the gap between actionability and benefit remains a clinical challenge attributed to multiple factors including the complex, multi-factorial relationship between molecular status and response to therapy. These differences go beyond simple disease states and may be reflective of multiple clinically relevant features including age, sex, and race/ethnicity. Methods: We implemented a functional precision medicine (FPM) program where patients with advanced pediatric cancers were prospectively profiled via high-throughput drug sensitivity testing (DST) of FDA-approved agents on patient-derived tumor cells as well as genomics testing. The objective was to investigate the clinical utility and benefit of FPM guidance in the treatment of pediatric cancer and elucidate the relationship between molecular status of patients’ diseases and treatment responses. We generated DST data (n = 21 patients) and genomic profiling data (n = 20 patients) on pediatric cancer patients in Miami, FL, as well as post-hoc whole exome and transcriptome sequencing data (n = 13 patients) and investigated three specific relationships. Results: We analyzed the relationship between racial/ethnic background and functional response to anti-cancer agents, determining potential differences in response to therapeutic classes. Next, we examined relationships between functional response and cancer type, identifying an unanticipated lack of clustering between disease indications in patients with advanced pediatric cancers. Finally, we applied an explainable machine learning (xML) framework to the functional genomic dataset to develop multi-omics biomarker hypotheses for the chemotherapy agent idarubicin, pinpointing a potential multi-cancer relationship between response to idarubicin and known disease mechanisms in acute myeloid leukemia (AML), the sole indication where idarubicin is approved. We further present additional proof-of-concept studies generating biomarker hypotheses via xML, demonstrating a framework for development of multi-omics biomarkers. Conclusions: We are now expanding our pan-pediatric cancer functional genomics dataset through an NIMHD-funded expansion cohort (NCT05857969, n = 65 patients) to further investigate multi-omics relationships between functional and molecular characteristics and understand the role of race/ethnicity in the complex relationship.

Children with rare, relapsed or refractory cancers often face limited treatment options, and few predictive biomarkers are available that can enable personalized treatment recommendations. The implementation of functional precision medicine (FPM), which combines genomic profiling with drug sensitivity testing (DST) of patient-derived tumor cells, has potential to identify treatment options when standard-of-care is exhausted. The goal of this prospective observational study was to generate FPM data for pediatric patients with relapsed or refractory cancer. The primary objective was to determine the feasibility of returning FPM-based treatment recommendations in real time to the FPM tumor board (FPMTB) within a clinically actionable timeframe (<4 weeks). The secondary objective was to assess clinical outcomes from patients enrolled in the study. Twenty-five patients with relapsed or refractory solid and hematological cancers were enrolled; 21 patients underwent DST and 20 also completed genomic profiling. Median turnaround times for DST and genomics were within 10 days and 27 days, respectively. Treatment recommendations were made for 19 patients (76%), of whom 14 received therapeutic interventions. Six patients received subsequent FPM-guided treatments. Among these patients, five (83%) experienced a greater than 1.3-fold improvement in progression-free survival associated with their FPM-guided therapy relative to their previous therapy, and demonstrated a significant increase in progression-free survival and objective response rate compared to those of eight non-guided patients. The findings from our proof-of-principle study illustrate the potential for FPM to positively impact clinical care for pediatric and adolescent patients with relapsed or refractory cancers and warrant further validation in large prospective studies. ClinicalTrials.gov registration: NCT03860376 .

1551 Background: Pediatric and adult patients with rare, relapsed, or refractory cancers often have few treatment options. Precision medicine approaches are often the first strategy used to identify salvage therapy options when standard treatments fail. Despite the significant clinical benefit to advanced cancer patients, multiple genomics precision medicine trials have revealed important constraints for patients that lack treatments matched to mutations or biomarkers and have highlighted challenges in drug accessibility associated with novel targeted therapies identified through genomics precision medicine. Current clinical findings from large-scale studies demonstrate ~10% of cancer patients receive clinical benefit from genomics-guided therapies - in part due to limited insight into the complex relationship between tumor molecular characteristics and patient response. Methods: We implemented a functional precision medicine (FPM) approach combining genomic tumor profiling with high-throughput drug sensitivity testing (DST) of FDA-approved agents on patient-derived tumor cells to identify treatment options when standard-of-care is exhausted. Clinical utility and benefit of this program was investigated via a clinical trial (NCT03860376) at Nicklaus Children’s Hospital in Miami, FL. Results: We were returned DST data on 21 of 24 patients DST (median = 102 agents per sample) and genomic profiling on 20 of 24 patients. DST turnaround time was significantly below the 14 days required for clinical use (median = 10 days, p = 0.0012). FPM recommendations were returned to 19 (76%) patients, of which 14 patients underwent therapeutic intervention. Six patients received FPM-guided treatments, and five (83%) patients experienced a >1.3-fold improved progression-free survival over their previous therapy, significantly above the rate from physician’s choice (p = 0.0104). We subsequently opened pan-cancer FPM clinical studies for adults (n = 36 patients) and children (n = 65 patients). A key objective in these trials is optimizing our DST protocol for tissue samples of various sizes. Here, we report preliminary efforts to optimize our DST approach for tissue samples from resections, core biopsies, and fine-needle biopsies from primary and metastatic lesions. Conclusions: The findings from our feasibility study illustrate the potential for FPM to positively impact clinical care for pediatric/adolescent patients with relapsed/refractory cancers, and have supported initiation of currently enrolling clinical studies. An NIMHD-funded expansion cohort now enrolling at Nicklaus Children’s Hospital (NCT05857969, n = 65 patients), and a rare/relapsed/refractory adult patient cohort at Cleveland Clinic Florida (NCT06024603, n = 36 patients). These studies aim to further investigate the impact on clinical outcomes through the use of FPM to recommend treatment options. Clinical trial information: NCT06024603 , NCT05857969 , NCT04956198 , NCT03860376 .

Functional precision medicine (FPM), combining ex vivo drug sensitivity testing with genomic profiling to identify treatment options for recurrent/refractory cancer, is feasible and poised to accelerate. This forum explores the history of FPM, recent clinical advancements, and barriers to expanding the clinical utility and accessibility for pediatric/adolescent and adult cancers.

Abstract Current genomics-driven precision oncology identifies actionable mutations in < 10% of cancer patients. Pediatric cancer is especially challenging due to limited mutations and fewer genomics-guided options. Functional precision medicine (FPM) addresses this by integrating genomic profiling with rapid, high-throughput functional ex vivo drug testing on live patient-derived cells. However, there is lack of FPM prospective data showing clinical utility in pediatric cancers. In this prospective, non-randomized, single-arm study (NCT03860376), we investigated feasibility and impact of FPM in pediatric/adolescent with refractory/relapsed solid and hematologic cancers. Of 25 patients, 19 (76%) had FPM data reviewed by the FPM tumor board within four weeks (FPMTB), meeting the primary outcome of the study. Additionally, six patients received FPM-guided treatment. Among these 6 patients, 83% (5 patients) experienced a greater than 1.3-fold improved progression-free survival compared to their previous therapy, and together demonstrated a significant increase in progression-free survival and objective response rate versus physician’s choice-treated patients (8 patients). Post-hoc analysis showed that patients with the same subtype of cancer do not cluster together, reinforcing the concept of optimizing cancer treatments one patient at a time (n-of-1 approach). Additionally, our study used a novel artificial intelligence/machine learning (AI/ML) platform that leveraged drug responses and sequencing data to identify novel biomarkers of drug efficacy and gain potential mechanistic insights within specific subsets of pediatric cancer patients. The findings from our proof-of-principle study illustrate the impact of FPM for relapsed/refractory pediatric/adolescent cancer patients, highlight future integrations of FPM and AI/ML, and support ongoing patient cohort expansion (NCT05857969).

Personalized medicine often serves as the first salvage therapy strategy when standard oncology treatments fail. However, most precision oncology approaches rely on molecular profiling which, unfortunately, provides therapeutic options for less than 10% of cancer patients. Functional precision medicine (FPM) complements molecular profiling by combining it with rapid, high-throughput drug testing on live patient cells to identify promising treatment options. In this study, we investigated the efficacy of FPM in the management of pediatric patients with recurrent and/or refractory cancers. We enrolled 25 pediatric/young adult patients with refractory solid or liquid cancers in this clinical trial (number NCT03860376). Enrolled patients represented the breadth of cancer indications generally presenting in pediatric patients: acute lymphoblastic leukemia (3 patients), acute myeloid leukemia (3 patients), astrocytoma (1 patient), ependymoma (1 patient), Ewing’s sarcoma (4 patients), glioblastoma (1 patient), malignant rhabdoid tumor (1 patient), medulloblastoma (1 patient), neuroblastoma (1 patient), osteosarcoma (4 patients), rhabdomyosarcoma (4 patients) and Wilms’ tumor (1 patient). We used a functional ex vivo drug sensitivity test (DST) panel encompassing 40 formulary drugs frequently used at Nicklaus Children’s Hospital and 47 non-formulary drugs approved by FDA for cancer treatment, as well as drugs from phase III and IV clinical trials. Drug sensitivity scores (DSS) were calculated for each drug based on cancer cells’ responses. DST results were then combined with results from targeted mutation profiles to match actionable mutations with selective targeted therapies. FPM and molecular data were prospectively generated and treatment recommendations were provided to an FPM Molecular Tumor Board (MTB) of clinicians. In total, 19 of 25 patients (76%) had complete functional and molecular profiling data provided to the MTB to support clinical decision-making. Six patients had their subsequent treatment guided by FPM recommendations, of which 83% (five of six patients) demonstrated greater than 1.3x increased progression-free survival compared to their previous therapy. Interestingly, hierarchical clustering analysis of DST results shows that patients with the same subtype of cancer do not cluster together, and no cancer subtype is differentially represented in either high-level cluster, suggesting the importance of functional profiling to provide deeper insight into individual patient pharmacological response. This FPM study is the first pediatric cancer study to enroll both solid and hematologic cancers regardless of tumor type, and the first FPM study in the United States to generate prospective treatment data on pediatric oncology patients. We illustrate the feasibility and efficacy of FPM to meet the needs of cancer patients with both liquid and solid tumors, especially for high-risk populations such as pediatric cancer patients. Citation Format: Arlet Maria Acanda de la Rocha, Maggie Fader, Ebony R. Coats, Joseph Dunn, Leat Perez, Carolina Velasquez, Jeanette Galano, Cima Saghira, Ileana Sotto, Yana Vorontsova, Ziad Khatib, Haneen Abdella, Cristina M. Andrade-Feraud, Alexa Jacome, Victoria Reis, Lilliam Rimblas, Nicole Tomas, Paula S. Espinal, Noah Berlow, Tomás R. Guilarte, Jennifer McCafferty-Fernandez, Daria Salyakina, Diana J. Azzam. Efficacy of a functional precision medicine approach in relapsed/refractory pediatric cancer patients: results from a prospective clinical study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB358.

Background Systemic therapy for metastatic clear cell sarcoma (CCS) bearing EWSR1-CREB1/ATF1 fusions remains an unmet clinical need in children, adolescents, and young adults. Methods To identify key signaling pathway vulnerabilities in CCS, a multi-pronged approach was taken: (i) genomic and transcriptomic landscape analysis, (ii) integrated chemical biology interrogations, (iii) development of CREB1/ATF1 inhibitors, and (iv) antibody-drug conjugate testing (ADC). The first approach encompassed DNA exome and RNA deep sequencing of the largest human CCS cohort yet reported consisting of 47 patient tumor samples and 8 cell lines. Results Sequencing revealed recurrent mutations in cell cycle checkpoint, DNA double-strand break repair or DNA mismatch repair genes, with a correspondingly low to intermediate tumor mutational burden. DNA multi-copy gains with corresponding high RNA expression were observed in CCS tumor subsets. CCS cell lines responded to the HER3 ADC patritumab deruxtecan in a dose-dependent manner in vitro, with impaired long term cell viability. Conclusion These studies of the genomic, transcriptomic and chemical biology landscape represent a resource ‘atlas’ for the field of CCS investigation and drug development. CHK inhibitors are identified as having potential relevance, CREB1 inhibitors non-dependence of CCS on CREB1 activity was established, and the potential utility of HER3 ADC being used in CCS is found.

Over the past 25 years, chemotherapy regimens for osteosarcoma have failed to improve the 65-70% long-term survival rate. Radiation therapy is generally ineffective except for palliative care. We here investigated whether osteosarcoma can be sensitized to radiation therapy targeting specific molecules in osteosarcoma. Large-scale RNA sequencing analysis in osteosarcoma tissues and cell lines revealed that FGFR1 is the most frequently expressed receptor tyrosine kinase in osteosarcoma. Nuclear FGFR1 (nFGFR1) was observed by subcellular localization assays. The functional studies using a FGFR1IIIb antibody or small molecule FGFR1 inhibitors showed that nFGFR1, but not membrane-bound FGFR1, induces G2 cell-cycle checkpoint adaptation, cell survival and polyploidy following irradiation in osteosarcoma cells. Further, the activation of nFGFR1 induces Histone H3 phosphorylation at Ser 10 and c-jun/c-fos expression to contribute cell survival rendering radiation resistance. Furthermore, an in vivo mouse study revealed that radiation resistance can be reversed by the inhibition of nFGFR1. Our findings provide insights into the potential role of nFGFR1 to radiation resistance. Thus, we propose nFGFR1 could be a potential therapeutic target or a biomarker to determine which patients might benefit from radiation therapy.

Correctly diagnosing a rare childhood cancer such as sarcoma can be critical to assigning the correct treatment regimen. With a finite number of pathologists worldwide specializing in pediatric/young adult sarcoma histopathology, access to expert differential diagnosis early in case assessment is limited for many global regions. The lack of highly-trained sarcoma pathologists is especially pronounced in low to middle-income countries, where pathology expertise may be limited despite a similar rate of sarcoma incidence. To address this issue in part, we developed a deep learning convolutional neural network (CNN)-based differential diagnosis system to act as a pre-pathologist screening tool that quantifies diagnosis likelihood amongst trained soft-tissue sarcoma subtypes based on whole histopathology tissue slides. The CNN model is trained on a cohort of 424 centrally-reviewed histopathology tissue slides of alveolar rhabdomyosarcoma, embryonal rhabdomyosarcoma and clear-cell sarcoma tumors, all initially diagnosed at the originating institution and subsequently validated by central review. This CNN model was able to accurately classify the withheld testing cohort with resulting receiver operating characteristic (ROC) area under curve (AUC) values above 0.889 for all tested sarcoma subtypes. We subsequently used the CNN model to classify an externally-sourced cohort of human alveolar and embryonal rhabdomyosarcoma samples and a cohort of 318 histopathology tissue sections from genetically engineered mouse models of rhabdomyosarcoma. Finally, we investigated the overall robustness of the trained CNN model with respect to histopathological variations such as anaplasia, and classification outcomes on histopathology slides from untrained disease models. Overall positive results from our validation studies coupled with the limited worldwide availability of sarcoma pathology expertise suggests the potential of machine learning to assist local pathologists in quickly narrowing the differential diagnosis of sarcoma subtype in children, adolescents, and young adults.

Abstract Background Metastatic epithelioid sarcoma (EPS) remains a largely unmet clinical need in children, adolescents and young adults despite the advent of EZH2 inhibitor tazemetostat. Methods In order to realise consistently effective drug therapies, a functional genomics approach was used to identify key signalling pathway vulnerabilities in a spectrum of EPS patient samples. EPS biopsies/surgical resections and cell lines were studied by next‐generation DNA exome and RNA deep sequencing, then EPS cell cultures were tested against a panel of chemical probes to discover signalling pathway targets with the most significant contributions to EPS tumour cell maintenance. Results Other biologically inspired functional interrogations of EPS cultures using gene knockdown or chemical probes demonstrated only limited to modest efficacy in vitro. However, our molecular studies uncovered distinguishing features (including retained dysfunctional SMARCB1 expression and elevated GLI3, FYN and CXCL12 expression) of distal, paediatric/young adult‐associated EPS versus proximal, adult‐associated EPS. Conclusions Overall results highlight the complexity of the disease and a limited chemical space for therapeutic advancement. However, subtle differences between the two EPS subtypes highlight the biological disparities between younger and older EPS patients and emphasise the need to approach the two subtypes as molecularly and clinically distinct diseases.

Rhabdomyosarcoma (RMS) is a mesenchymal malignancy phenocopying muscle and is among the leading causes of death from childhood cancer. Metastatic alveolar rhabdomyosarcoma is the most aggressive subtype with an 8% 5-yr disease-free survival rate when a chromosomal fusion is present and a 29% 5-yr disease-free survival rate when negative for a fusion event. The underlying biology of PAX-fusion-negative alveolar rhabdomyosarcoma remains largely unexplored and is exceedingly rare in Li-Fraumeni syndrome patients. Here, we present the case of an 11-yr-old male with fusion-negative alveolar rhabdomyosarcoma studied at end of life with a comprehensive functional genomics characterization, resulting in identification of potential therapeutic targets for broader investigation.

An amendment to this paper has been published and can be accessed via the original article.

Wilms’ tumor is the most common childhood kidney cancer. Two distinct histological subtypes of Wilms’ tumor have been described: tumors lacking anaplasia (the favorable subtype) and tumors displaying anaplastic features (the unfavorable subtype). Children with favorable disease generally have a very good prognosis, while those with anaplasia are oftentimes refractory to standard treatments and suffer poor outcomes. MYCN dysregulation has been associated with a number of pediatric cancers including the anaplastic subtype of Wilms’ tumor. In this context, we undertook a functional genomics approach to uncover novel therapeutic strategies for those patients with anaplastic Wilms’ tumor. Genomic analysis and in vitro experimentation demonstrate that Wilms’ tumor cell growth can be reduced by modulating MYCN overexpression via BRD4 inhibition. We observed a time dependent reduction of MYCN and MYC protein levels upon BRD4 inhibition in Wilms’ tumor cell lines which led to increased cell death and suppressed proliferation. We suggest that AZD5153, a novel dual-BRD4 inhibitor, can reduce MYCN levels and should be further explored for its therapeutic potential against Wilms’ tumor.

Multilateral wells are an evolution of horizontal wells in which several wellbore branches radiate from the main borehole. In the last two decades, multilateral wells have been increasingly utilized in producing hydrocarbon reservoirs. The main advantage of using such technology against conventional and single-bore wells comes from the additional access to reservoir rock by maximizing the reservoir contact with fewer resources. Today, multilateral wells are rapidly becoming more complex in both designs and architecture (i.e., extended reach wells, maximum reservoir contact, and extreme reservoir contact wells). Certain multilateral design templates prevail in the industry, such as fork and fishbone types, which tend to be populated throughout the reservoir of interest with no significant changes to the original architecture and, therefore, may not fully realize the reservoir's potential. Placement of optimal multilateral wells is a multivariable problem, which is a function of determining the best well locations and trajectories in a hydrocarbon reservoir with the ultimate objectives of maximizing productivity and recovery. The placement of the multilateral wells can be subject to many constraints such as the number of wells required, maximum length limits, and overall economics. This paper introduces a novel technology for placement of multilateral wells in hydrocarbon reservoirs utilizing a transshipment network optimization approach. This method generates scenarios of multiple wells with different designs honoring the most favorable completion points in a reservoir. In addition, the algorithm was developed to find the most favorable locations and trajectories for the multilateral wells in both local and global terms. A partitioning algorithm is uniquely utilized to reduce the computational cost of the process. The proposed method will not only create different multilateral designs; it will justify the trajectories of every borehole section generated. The innovative method is capable of constructing hundreds of multilateral wells with design variations in large-scale reservoirs. As the complexity of the reservoirs (e.g., active forces that influence fluid mobility) and heterogeneity dictate variability in performance at different area of the reservoir, multilateral wells should be constructed to capture the most productive zones. The new method also allows different levels of branching for the laterals (i.e., laterals can emanate from the motherbore, from other laterals or from subsequent branches). These features set the stage for a new generation of multilateral wells to achieve the most effective reservoir contact.

Specific mutations in the RET proto-oncogene are associated with multiple endocrine neoplasia type 2A, a hereditary syndrome characterized by tumorigenesis in multiple glandular elements. In rare instances, MEN2A-associated germline RET mutations have also occurred with non-MEN2A associated cancers. One such germline mutant RET mutation occurred concomitantly in a young adult diagnosed with alveolar rhabdomyosarcoma, a pediatric and young adult soft-tissue cancer with a generally poor prognosis. Although tumor tissue samples were initially unable to provide a viable cell culture for study, tumor tissues were sequenced for molecular characteristics. Through a hierarchical clustering approach, the index case sample was matched to several genetically similar cell models, which were transformed to express the same mutant RET as the index case and used to explore potential therapeutic options for mutant RET -bearing alveolar rhabdomyosarcoma. We also determined whether the RET mutation associated with the index case caused synthetic lethality to select clinical agents. From our investigation, we did not identify synthetic lethality associated with the expression of that patient's RET variant, and overall we did not find experimental evidence for the role of RET in rhabdomyosarcoma progression.

As high-throughput sequencing experiments become more widely used in pre-clinical and clinical settings, pharmacogenetic and pharmacogenomic biomarker development plays an increasingly important role in oncology drug development pipelines and programs. Consequently, computer-based learning approaches have entered into use at multiple stages in pre-clinical and clinical pipelines. However, few approaches are available to identify interpretable and implementable biomarkers of response early in the drug development process when only small pre-clinical data packages are available. To address the need for early-stage biomarker development using pre-clinical tumor models, we have adapted the previously published Probabilistic Target Inhibitor Map (PTIM) platform to the challenge of biomarker hypothesis development, and denoted this approach the Probabilistic Target Map-Biomarker (PTM-Biomarker). In this article, we detail the history and design philosophy of PTM-Biomarker, and present two case studies using the biomarker discovery tool to illustrate its utility in guiding cancer drug development. © 2021 Wiley Periodicals LLC.

Preclinical cancer research ranges from in vitro studies that are inexpensive and not necessarily reflective of the tumor microenvironment to mouse studies that are better models but prohibitively expensive at scale. Chorioallantoic membrane (CAM) assays utilizing Japanese quail (Coturnix japonica) are a cost-effective screening method to precede and minimize the scope of murine studies for anti-cancer efficacy and drug toxicity. To increase the throughput of CAM assays we have built and optimized an 11-day platform for processing up to 200 quail eggs per screening to evaluate drug efficacy and drug toxicity caused by a therapeutic. We demonstrate ex ovo concordance with murine in vivo studies, even when the in vitro and in vivo studies diverge, suggesting a role for this quail shell-free CAM xenograft assay in the validation of new anti-cancer agents.

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood with a propensity to metastasize. Current treatment for patients with RMS includes conventional systemic chemotherapy, radiation therapy, and surgical resection; nevertheless, little to no improvement in long term survival has been achieved in decades—underlining the need for target discovery and new therapeutic approaches to targeting tumor cells or the tumor microenvironment. To evaluate cross-species sarcoma extracellular matrix production, we have used murine models which feature knowledge of the myogenic cell-of-origin. With focus on the RMS/undifferentiated pleomorphic sarcoma (UPS) continuum, we have constructed tissue microarrays of 48 murine and four human sarcomas to analyze expression of seven different collagens, fibrillins, and collagen-modifying proteins, with cross-correlation to RNA deep sequencing. We have uncovered that RMS produces increased expression of type XVIII collagen alpha 1 (COL18A1), which is clinically associated with decreased long-term survival. We have also identified significantly increased RNA expression of COL4A1, FBN2, PLOD1, and PLOD2 in human RMS relative to normal skeletal muscle. These results complement recent studies investigating whether soft tissue sarcomas utilize collagens, fibrillins, and collagen-modifying enzymes to alter the structural integrity of surrounding host extracellular matrix/collagen quaternary structure resulting in improved ability to improve the ability to invade regionally and metastasize, for which therapeutic targeting is possible.