Desmoplastic Small Round Cell Tumor Research Articles

Comprehensive Transcriptomic Analysis of EWSR1::WT1 Targets Identifies CDK4/6 Inhibitors as an Effective Therapy for Desmoplastic Small Round Cell Tumors.

EWSR1::WT1 is essential for desmoplastic small round cell tumors and upregulates the cyclin D-CDK4/6-RB axis that can be targeted with palbociclib, providing a targeted therapeutic strategy for treating this deadly tumor type.

Enzalutamide induces cytotoxicity in desmoplastic small round cell tumor independent of the androgen receptor

Desmoplastic Small Round Cell Tumor (DSRCT) is a rare, pediatric cancer caused by the EWSR1::WT1 fusion protein. DSRCT predominantly occurs in males, which comprise 80-90% of the patient population. While the reason for this male predominance remains unknown, one hypothesis is that the androgen receptor (AR) plays a critical role in DSRCT and elevated testosterone levels in males help drive tumor growth. Here, we demonstrate that AR is highly expressed in DSRCT relative to other fusion-driven sarcomas and that the AR antagonists enzalutamide and flutamide reduce DSRCT growth. However, despite these findings, which suggest an important role for AR in DSRCT, we show that DSRCT cell lines form xenografts in female mice at the same rate as male mice and AR depletion does not significantly alter DSRCT growth in vitro. Further, we find that AR antagonists reduce DSRCT growth in cells depleted of AR, establishing an AR-independent mechanism of action. These findings suggest that AR dependence is not the reason for male predominance in DSRCT and that AR-targeted therapies may provide therapeutic benefit primarily through an AR-independent mechanism that requires further elucidation.

Multimodality imaging of ureteral desmoplastic small round cell tumor: a case description and literature analysis of 18F-fluoro-2-deoxy-d-glucose positron emission tomography-computed tomography findings.

Multimodality imaging of ureteral desmoplastic small round cell tumor: a case description and literature analysis of 18F-fluoro-2-deoxy-d-glucose positron emission tomography-computed tomography findings.

Imaging of desmoplastic small round-cell tumor on 68Ga-FAPI PET/CT

Imaging of desmoplastic small round-cell tumor on 68Ga-FAPI PET/CT

Abstract 6932: Single-cell multiomics profiling reveals heterogeneous transcriptional programs and microenvironment in desmoplastic small round cell tumors

Abstract Background: Desmoplastic Small Round Cell Tumor (DSRCT) is a rare, aggressive sarcoma primarily affecting young males. Despite being driven by the unique oncogenic transcription factor (TF) EWSR1-WT1, and a monotonous morphology, DSRCT cells display a polyphenotypic differentiation of unknown etiology. Methods: To explore DSRCT heterogeneity, we characterized a series of patient samples by single-cell, spatial, and bulk multi-omics. We integrated patients’ data with bulk RNA-sequencing, ChIP-sequencing, and ATAC-sequencing data generated in a DSRCT cell line model upon EWSR1-WT1 transcriptional silencing. Results: Single-cell RNA-sequencing (scRNA-seq) on 11 patient samples identified recurrent subpopulations of DSRCT tumor cells, including lineage-, metabolism-, and pseudostate-related clusters. These subpopulations showed overlapping gene modules and lacked copy number variation diversity, suggesting transcriptional plasticity as a potential source of tumor heterogeneity. We first investigated whether cell-intrinsic mechanisms may drive DSRCT intra-tumor heterogeneity. Using an in-house-developed assay, we found limited variability in EWSR1-WT1 transcript expression. Preclinical modeling defined an EWSR1-WT1 regulon, used as a surrogate for EWSR1-WT1 TF activity. Integration with scRNA-seq data showed that high EWSR1-WT1 activity was associated with lineage-related states, while glycolytic and profibrotic states correlated with low EWSR1-WT1 activity. Single-cell ATAC-seq with scRNA-seq (Multiome) on one patient sample identified TF motifs related to developmental processes - e.g., SOX, FOX, and GATA - as the most differentially enriched across clusters. Interestingly, EGR1 regulon activity showed an inverse correlation with EWSR1-WT1 and Androgen Receptor regulons’ activity, in line with preclinical data, where ATAC-seq showed increased accessibility of EGR1 upon EWSR1-WT1 silencing. We next investigated cell-extrinsic factors by spatial transcriptomics in six patient samples. Glycolytic and profibrotic subpopulations localized within hypoxic niches at the tumor periphery, in direct proximity to cancer-associated fibroblasts (CAFs), which promoted tumor growth in vitro, as assessed in DSRCT cells/CAFs co-culture assays. Finally focusing on inter-tumor heterogeneity, the prognostic evaluation of scRNA-seq-derived signatures revealed that a tumor cell epithelial signature correlated with improved patient survival in a cohort of 29 DSRCT samples profiled with bulk RNA-sequencing. Conclusion: DSRCT heterogeneity is driven by combined cell-intrinsic and -extrinsic mechanisms, including EWSR1-WT1 DNA-binding activity and interaction with CAFs. Gene signatures associated with specific DSRCT subpopulations correlated with prognosis, highlighting the clinical relevance of our findings. Citation Format: Clémence Henon, Julien Vibert, Thomas Eychenne, Nadège Gruel, Léo Colmet-Daage, Carine Ngo, Marlène Garrido, Nicolas Dorvault, Maria Eugenia Marques Da Costa, Antonin Marchais, Asuka Kawachi, Madison Lenormand, Clémence Astier, Roman Chabanon, Benjamin Verret, Rastislav Bahleda, Axel Le Cesne, Fatima Mechta-Grigoriou, Charles Honoré, Matthieu Faron, Olivier Delattre, Joshua J Waterfall, Sarah Watson, Sophie Postel-Vinay. Single-cell multiomics profiling reveals heterogeneous transcriptional programs and microenvironment in desmoplastic small round cell tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6932.

Abstract 6: Defining and therapeutically targeting a fusion-derived public neoantigen in desmoplastic small round cell tumor using T cell receptor gene therapy

Abstract Sarcomas are a heterogenous group of mesenchymal cell malignancies that are difficult to treat and often respond poorly to current immunotherapies. Approximately 30% of sarcomas are associated with oncogenic driver fusion proteins. Desmoplastic small round cell tumor (DSRCT) is a prototypical fusion-driven sarcoma defined by a pathognomonic EWSR1-WT1 fusion event. The resultant EWSR1-WT1 fusion protein contains a shared junctional amino acid sequence that is clonally conserved and significantly divergent from normal human proteins. Consequently, the EWSR1-WT1 fusion might yield a highly immunogenic shared, or public, neoantigen (NeoAg) that may serve as a target for novel immunotherapeutic approaches.Using a functional HLA-immunoprecipitation/mass spectrometry (HLA-IP/MS) screen, we identified a 9-amino acid peptide sequence derived from the junction of the most common EWSR1-WT1 fusion protein that is presented in the context of the prevalent HLA-A*03 and -A*11 alleles. We confirmed that HLA-A*03+ DSRCT cells physiologically present the same peptide sequence. Using fluorophore-conjugated HLA-multimers loaded with the HLA-IP/MS-derived fusion NeoAg, we identified a rare population of circulating NeoAg-specific CD8+ T cells in HLA+ DSRCT patients. Through antigen-directed clonal expansion, we discovered n=3 HLA-A*03-restricted and n=1 HLA-A*11-restricted fusion NeoAg-specific T cell clones and retrieved the paired TCRαβ gene sequences of their T cell receptors (TCRs) using 10x single-cell sequencing. Polyclonal CD8+ T cells transduced with candidate TCRαβ gene sequences robustly upregulated TNFα after coculture with HLA+/Fusion+ target cells but not HLA−/Fusion+ or HLA+/Fusion− control cells. Further, T cells expressing candidate TCRs, but not viral-protein-specific TCRs, lysed HLA+ DSRCT cells in vitro and controlled established DSRCT tumors in vivo. Finally, we discovered that one TCR was capable of cross HLA allele fusion NeoAg recognition and could lyse both HLA-A*03+ and -A*11+ DSRCT cells. These findings imply that a single TCR therapeutic could cover >36% of North American DSRCT patients.Collectively, our data establish for the first time that DSRCT cells present a junction-spanning fusion-derived neoantigen in the context of two prevalent HLA alleles that may be therapeutically targeted using TCR gene therapy. These data lay the foundation for first-in-human clinical translation of a T-cell based therapy targeting EWSR1-WT1. More broadly, these findings establish proof-of-principle that recurrent fusion proteins are an actionable source of immunogenic public NeoAgs, providing a framework for developing targeted immunotherapies for other fusion-driven malignancies. Citation Format: Lauren Banks, Hannah Arkin, Smita Chandran, Emily Slotkin, Madelyn Espinosa-Cotton, Neerav Shukla, Luc Morris, Marc Ladanyi, Andrew Kung, Martin Klatt, Christopher Klebanoff. Defining and therapeutically targeting a fusion-derived public neoantigen in desmoplastic small round cell tumor using T cell receptor gene therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6.

Abstract 2851: Characterization of neogenes in desmoplastic small round cell tumors

Abstract Desmoplastic Small Round Cell Tumor (DSRCT) is a rare, soft tissue sarcoma caused by the EWS::WT1 fusion protein (FP). The FP acts as an aberrant transcription factor with oncogenic properties. Recently, oncogenic chimeric transcription factors (OCTF), such as EWS::WT1, were discovered to induce the expression of novel transcripts in otherwise silent genomic regions. These neogenes (NGs) are highly specific to each OCTF and not detected in normal tissue. 37 NGs were found to be associated with the EWS::WT1 FP.We explored the NGs to characterize their expression and regulation in a cohort of MD Anderson Cancer Center patients. We annotated and counted the NGs from the bulk RNA-seq data of 37 specimens. After fusion detection, only 22/37 specimens harbored the EWS::WT1 FP. We found that only the same 22 specimens robustly expressed DSRCT-specific NGs. Interestingly the NGs were heterogeneously expressed, suggesting that there may be patient-specific differences. Single-nucleus RNA-sequencing (snRNA-seq) of Ewing sarcoma (ES), CIC::DUX4 sarcoma (CDS), DSRCT, and osteosarcoma revealed that only the three sarcomas driven by an OCTF robustly expressed NGs. Notably, the DSRCT-specific NGs were only expressed in DSRCT. Similarly, ES and CDS only expressed their subtype-specific NGs. Given the robust expression of the DSRCT-specific NGs in DSRCT, we asked if the EWS::WT1 FP regulated the expression of the NGs. Knockdown (KD) of the EWS::WT1 FP in four DSRCT cell lines showed a consistent reduction in DSRCT-specific NGs. While there was variability in NG expression and EWS::WT1 FP KD sensitivity, we identified seven NGs decreased by at least 75% in all four cell lines and an additional eight NGs with 75% reduction across three cell lines. BOD-DSRCT and SK-DSRCT2 had the largest number of NGs reduced after KD, with 25/37 and 20/37 NGs with 75% expression reduction, respectively. EWS::WT1 FP has two known isoforms generated by alternative splicing in the WT1 domain that includes or excludes three amino acids, lysine, threonine, and serine (KTS) between zinc fingers 3 and 4, producing E+KTS and E-KTS isoforms. By transducing one or both isoforms into the mesothelial cell line LP9, we found 3/37 NGs were induced by the E+KTS isoform and 17/37 were induced by the E-KTS isoform, suggesting that the E-KTS isoform is primarily responsible for NG expression. Current work is underway investigating the relationship between EWS::WT1 FP binding and NG expression and the potential for NG to produce novel peptides that could serve as DSRCT immunotherapy targets. Citation Format: Danh Truong, Justin Magrath, Sean Lee, Joseph Ludwig. Characterization of neogenes in desmoplastic small round cell tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2851.

Abstract 3583: Enzalutamide and flutamide induce cytotoxicity in desmoplastic small round cell tumor independent of the androgen receptor

Abstract Desmoplastic Small Round Cell Tumor (DSRCT) is a rare, pediatric cancer caused by the EWSR1::WT1 fusion protein. DSRCT predominantly occurs in males, which comprise 80-90% of the patient population. While the reason for the male prevalence remains unknown, one hypothesis is that the androgen receptor (AR), when stimulated by testosterone in males, plays a critical role in DSRCT tumor growth. As a rare pediatric cancer, DSRCT model systems including cell lines and patient-derived xenografts are scarce. Further, DSRCT cell lines have been thought to seed xenograft tumors poorly, with studies commonly using 5-10 million cells for one xenograft. Using a recently established DSRCT cancer stem cell (CSC) model, we sought to establish DSRCT xenografts from fewer cells to enable large-scale xenograft feasibility and reliability. To our surprise, we were able to consistently seed tumors with as few as 100 cells, not only from CSC spheres but also from standard adherent cells. We hypothesized that mouse sex may explain our ability to seed xenografts with so few cells, as many previous studies have utilized female mice. This observation led us to comprehensively investigate the role of the AR in DSRCT. Here, we demonstrate that AR is highly expressed in DSRCT relative to other fusion-driven sarcomas and that the AR antagonists - enzalutamide and flutamide - reduce DSRCT growth. We further elucidate a novel interaction between AR and EWSR1::WT1, which may explain their co-occupancy in a subset of regulatory genomic regions. However, despite these findings, which suggest an essential role for AR in DSRCT, we find that DSRCT cell lines can form xenografts in female mice at the same rate as male mice and AR depletion does not significantly alter DSRCT growth in vitro. Further, we demonstrate that AR antagonists remain effective in DSRCT cells depleted of AR, establishing an AR-independent mechanism of action. Intriguingly, high-dose enzalutamide treatment reduces EWSR1::WT1 oncoprotein expression and could explain its toxicity. DSRCT cells express high levels of NR3 nuclear receptors, including the glucocorticoid receptor (GR). Enzalutamide was shown to act on GR in AR-negative prostate cancer cell lines, which could possibly explain its effect on DSRCT independent of AR. Further examination of this mechanism may provide promising therapeutic implications for DSRCT and other fusion proteins driven by the EWSR1 promoter. Citation Format: Justin W. Magrath, Ilon N. Goldberg, Danh D. Truong, Alifinai B. Hartono, Shruthi Sanjitha Sampath, Chandler E. Jackson, Anushka Ghosh, Derrick L. Cardin, Haitao Zhang, Joseph A. Ludiwg, Sean B. Lee. Enzalutamide and flutamide induce cytotoxicity in desmoplastic small round cell tumor independent of the androgen receptor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3583.

Abstract 2849: Palbociclib as a novel therapeutic for desmoplastic small round cell tumor

Abstract Desmoplastic small round cell tumor (DSRCT) is an aggressive, pediatric cancer caused by the EWSR1-WT1 fusion oncoprotein. Targeted therapies are lacking and the current standard of care, multimodal therapy, is insufficient, leading to a 5-year survival rate of less than 25%. While the EWSR1-WT1 oncoprotein is critical to growth in vitro, its importance has yet to be examined in vivo. Further, the set of EWSR1-WT1 downstream targets critical to oncogenesis and the mechanism by which the two EWSR1-WT1 isoforms regulate them remain underinvestigated. Here we generate a toolkit of DSRCT cell lines that deplete EWSR1-WT1 in a doxycycline (dox)-inducible manner. This toolkit enabled us to establish the essentiality of EWSR1-WT1 not only in vitro but also for the first time in vivo. Using this toolkit, we performed RNA sequencing on four DSRCT cell lines and established the most comprehensive analysis of EWSR1-WT1 downstream targets to date. We discovered novel mechanistic insights into EWSR1-WT1 functionality including the uniqueness of its transcriptional alterations as compared to native WT1, the direct role of EWSR1-WT1 binding in gene upregulation, and the dominant role of the E-KTS isoform in transcription. Given the rarity of DSRCT, we focused on downstream targets with existing inhibitors and perform a drug screen that identified the CDK4/6 inhibitor palbociclib as a novel DSRCT therapeutic. We found that the E-KTS isoform of EWSR1-WT1 binds to the CCND1 promoter, leads to CCND1 expression, and stimulates DSRCT growth through the CCND-CDK4/6-RB axis. Palbociclib treatment conversely reduced DSRCT growth by preventing retinoblastoma phosphorylation and blocking the transition from G1 to S phase. Palbociclib treatment was effective not only in vitro but also in vivo where it significantly reduced tumor growth in two xenograft models of DSRCT. Given these novel findings and palbociclib’s previous approval by the FDA for the treatment of breast cancer, we advance palbociclib as an exciting DSRCT therapy that warrants urgent clinical investigation. Citation Format: Justin W. Magrath, Shruthi Sanjitha Sampath, Dane A. Flinchum, Alifiani B. Hartono, Ilon N. Goldberg, Julia R. Boehling, Suzana D. Savkovic, Sean B. Lee. Palbociclib as a novel therapeutic for desmoplastic small round cell tumor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2849.

Abstract 5462: Single-cell spatial proteomic analysis to explore the spatial heterogeneity of desmoplastic small round cell tumors

Abstract Desmoplastic small round cell tumor (DSRCT) is a rare and usually incurable aggressive sarcoma subtype. All malignant cells harbor a pathognomonic EWSR1::WT1 fusion protein (FP). However, FP-targeted agents are nonexistent; less than 20% of patients survive beyond five years. The spatial organization of DSRCT, consisting of tumor nests surrounded by desmoplastic stroma, is a hallmark of this disease. Given this context, we seek to understand the spatial heterogeneity within DSRCT and the tumor-stroma interactions to reveal potential therapeutic vulnerabilities. We generated a 20-panel marker developed to interrogate the cellular constituents of the tumor microenvironment (TME) and to characterize the multilineage expression DSRCT, including androgen receptor (AR) and neuroendocrine signatures (NE). The following markers were used: DSRCT (ST6GALNAC, pan-Cytokeratin), Fibroblasts (Collagen, α-smooth muscle actin), Endothelial Cells (CD31, α-smooth muscle actin), T-cells (CD45, CD4, CD8), Macrophages (CD45, CD68, CD163, CD11c), AR/NE markers (AR, neural-specific enolase, synaptophysin). We explored the expression of these markers in a nine-patient cohort from 9 x 9 mm2 tissue sections imaged by the Lunaphore COMET. We used a deep learning model in Visiopharm to extract high-quality areas and segment cells based on their nucleus. The spatial image data was converted into matrix data, which could be further analyzed in R. We confirmed that the tumor nests are surrounded by dense desmoplasia by collagen expression. We identified tumor cells, fibroblasts, immune cells, and endothelial cells by thresholding for classical cell markers. ST6GALNAC, a sialyltransferase that was found to be highly expressed in DSRCT based on RNA-seq data, marked the tumor nests. Previous data from single-nucleus RNA-sequencing (snRNA-seq) showed that DSRCT exhibited three possible subtypes: AR+/NE-, AR-/NE+, and Hybrid AR+/NE+. We found concordance between the prior transcriptomic signatures and the proteomic markers. In tumor nests that were positive for AR, we found AR localized to the nucleus, suggesting downstream activation of this pathway. High AR expression was also correlated with positive expression of pan-cytokeratin in the tumor nests. Future work will focus on quantifying spatial relationships and patterns. This includes characterizing the spatial distribution of all cell types found in DSRCT, including fibroblasts, endothelial cells, and immune cells. We will also address whether tumor nest characteristics are associated with cell phenotype or DSRCT subtype. Citation Format: Danh Truong, Sandhya Krishnan, Clement Agyemang, Davis Ingram, Rossana Lascano, Akshay Basi, Javier Gomez, Jared Burks, Alexander Lazar, Joseph Ludwig. Single-cell spatial proteomic analysis to explore the spatial heterogeneity of desmoplastic small round cell tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5462.

Desmoplastic small round cell tumor of bone revealed by 18F-FDG PET/CT: a case report with literature review.

A 50-year-old male presented with neck and shoulder pain. Chest CT and 18F-FDG PET/CT revealed osteolytic bone destruction in the left first rib and thoracic vertebrae with increased FDG uptake. Rib biopsy pathology indicated desmoplastic small round cell tumor (DSRCT).18F-FDG PET/CT can accurately locate the distribution of DSRCT and further guide the location of needle biopsy to assist the DSRCT.

Targeting refractory/recurrent neuroblastoma and osteosarcoma with anti-CD3×anti-GD2 bispecific antibody armed T cells

BackgroundThe survival benefit observed in children with neuroblastoma (NB) and minimal residual disease who received treatment with anti-GD2 monoclonal antibodies prompted our investigation into the safety and potential clinical benefits...

Transcriptomic analysis identifies B-lymphocyte kinase as a therapeutic target for desmoplastic small round cell tumor cancer stem cell-like cells

Desmoplastic small round cell tumor (DSRCT) is an aggressive pediatric cancer caused by the EWSR1-WT1 fusion oncoprotein. The tumor is refractory to treatment with a 5-year survival rate of only 15–25%, necessitating the development of novel therapeutics, especially those able to target chemoresistant subpopulations. Novel in vitro cancer stem cell-like (CSC-like) culture conditions increase the expression of stemness markers (SOX2, NANOG) and reduce DSRCT cell line susceptibility to chemotherapy while maintaining the ability of DSRCT cells to form xenografts. To gain insights into this chemoresistant model, RNA-seq was performed to elucidate transcriptional alterations between DSRCT cells grown in CSC-like spheres and normal 2-dimensional adherent state. Commonly upregulated and downregulated genes were identified and utilized in pathway analysis revealing upregulation of pathways related to chromatin assembly and disassembly and downregulation of pathways including cell junction assembly and extracellular matrix organization. Alterations in chromatin assembly suggest a role for epigenetics in the DSRCT CSC-like state, which was further investigated with ATAC-seq, identifying over 10,000 differentially accessible peaks, including 4444 sphere accessible peaks and 6,120 adherent accessible peaks. Accessible regions were associated with higher gene expression, including increased accessibility of the CSC marker SOX2 in CSC-like culture conditions. These analyses were further utilized to identify potential CSC therapeutic targets, leading to the identification of B-lymphocyte kinase (BLK) as a CSC-enriched, EWSR1-WT1-regulated, druggable target. BLK inhibition and knockdown reduced CSC-like properties, including abrogation of tumorsphere formation and stemness marker expression. Importantly, BLK knockdown reduced DSRCT CSC-like cell chemoresistance, making its inhibition a promising target for future combination therapy.

Desmoplastic small round cell tumor a case report of a rare intra-abdominal tumor of the young adult

Desmoplastic small round cell tumor is a rare and highly aggressive mesenchymal tumor described as a distinct clinico-pathological entity in 1989 by Gerald . These tumors occur mainly in the peritoneal cavity,although other primary sites, such as testicular, ovarian, thoracic, pulmonary, intracranial and head and neck regions have been reported. Clinical symptoms are non-specific. Diagnosis is based on histological analysis combined with immunohistochemical study. Histological study typically shows small round blue cells in nests separated by abundant desmoplastic stroma associated with a single chromosomal translocation t(11:22) (p 13; q 12) involving the EWSR1 and WT1 genes. The prognosis is particularly poor, with median survival ranging from 17 to 25 months. Management of this tumor remains difficult, and current regimens do not achieve a significant cure rate despite the use of aggressive treatments such as polychemotherapy.

Metastatic Desmoplastic Small Round Cell Tumor - A Case Report and Review of the Literature

Desmoplastic small round cell tumour is a rare malignancy most often seen in the abdomen or pelvis of young men. Unfortunately, this disease is usually metastatic at diagnosis and has dismal outcomes. Since 1991, when it was first described as a distinct clinical entity by Gerald WL and Rosai J some 200 cases were reported. All cases are characterized by the chromosomal translocation t (11;22) (p13; q12), which results in a formation of EWSR1-WT1 fusion gene. The diagnosis of IDSRCT is often made with core-needle tissue biopsy specimens of laparoscopy or laparotomy. Immunohistochemical analyses have shown the co-expression of epithelial, neuronal, myogenic, and mesenchymal differentiation markers. Multimodal therapy is usually indicated with chemotherapy, surgery & radiotherapy. We report a rare and unusual case of an extensive abdominopelvic desmoplastic small round cell tumour with liver & lung metastases, in an adolescent male patient from Bangladesh who presented with abdominal mass, pain & hepatomegaly. With various difficulties in diagnosis, we ultimately reached at diagnosis by open biopsy and immunohistochemistry as desmoplastic small round cell tutor. Now patient is on multidrug chemotherapy (modified p6) protocol.

EWSR1::WT1 Fusions in Neoplasms Other Than Conventional Desmoplastic Small Round Cell Tumor: Three Tumors Occurring Outside the Female Genital Tract

Desmoplastic small round cell tumor (DSRCT) is a high-grade, primitive round cell sarcoma classically associated with prominent desmoplastic stroma, coexpression of keratin and desmin, and a characteristic EWSR1::WT1 gene fusion. DSRCT typically arises in the abdominopelvic cavity of young males with diffuse peritoneal spread and poor overall survival. Although originally considered to be pathognomonic for DSRCT, EWSR1::WT1 gene fusions have recently been detected in rare tumors lacking the characteristic morphologic and immunohistochemical features of DSRCT. Here, we report 3 additional cases of neoplasms other than conventional DSCRCT with EWSR1::WT1 gene fusions that occurred outside the female genital tract. Two occurred in the abdominopelvic cavities of a 27-year-old man and a 12-year-old girl, whereas the third arose in the axillary soft tissue of an 85-year-old man. All cases lacked prominent desmoplastic stroma and were instead solid and cystic with peripheral fibrous pseudocapsules and occasional intervening fibrous septa. Necrosis was either absent (1/3) or rare (2/3), and mitotic activity was low (<1 to 3 per 10 hpf). In immunohistochemical studies, there was expression of smooth muscle actin (3/3) and desmin (3/3), rare to focal reactivity for EMA (2/3), and variable expression of CK AE1/AE3 (1/3). Myogenin and MyoD1 were negative, and C-terminus-specific WT1 was positive in both cases tested (2/2). All 3 tumors followed a more indolent clinical course with 2 cases demonstrating no evidence of disease at 20 and 44 months after resection. The patient from case 3 died of other causes at 14 months with no evidence of recurrence. DNA methylation profiling showed that the 3 cases clustered with DSRCT; however, they demonstrated fewer copy number variations with 2 cases having a flat profile (0% copy number variation). Differential methylation analysis with hierarchical clustering further showed variation between the 3 cases and conventional DSRCT. Although further study is needed, our results, in addition to previous reports, suggest that EWSR1::WT1 gene fusions occur in rare and seemingly distinctive tumors other than conventional DSRCT with indolent behavior. Proper classification of these unusual soft tissue tumors with EWSR1::WT1 gene fusions requires direct correlation with tumor morphology and clinical behavior, which is essential to avoid overtreatment with aggressive chemotherapy.

CXCR4-directed PET/CT with [68 Ga]Ga-pentixafor in solid tumors—a comprehensive analysis of imaging findings and comparison with histopathology

BackgroundC-X-C motif chemokine receptor 4 (CXCR4) is overexpressed in various solid cancers and can be targeted by CXCR4-directed molecular imaging. We aimed to characterize the in-vivo CXCR4 expression in patients affected with solid tumors, along with a comparison to ex-vivo findings.MethodsA total 142 patients with 23 different histologically proven solid tumors were imaged with CXCR4-directed PET/CT using [68 Ga]Ga-pentixafor (total number of scans, 152). A semi-quantitative analysis of the CXCR4-positive tumor burden including maximum standardized uptake values (SUVmax) and target-to-background ratios (TBR) using blood pool was conducted. In addition, we performed histopathological staining to determine the immuno-reactive score (IRS) from patients’ tumor tissue and investigated possible correlations with SUVmax (by providing Spearman’s rho ρ). Based on imaging, we also assessed the eligibility for CXCR4-targeted radioligand therapy or non-radioactive CXCR4 inhibitory treatment (defined as more than five CXCR4-avid target lesions [TL] with SUVmax above 10).ResultsOne hundred three of 152 (67.8%) scans showed discernible uptake above blood pool (TBR > 1) in 462 lesions (52 primary tumors and 410 metastases). Median TBR was 4.4 (1.05–24.98), thereby indicating high image contrast. The highest SUVmax was observed in ovarian cancer, followed by small cell lung cancer, desmoplastic small round cell tumor, and adrenocortical carcinoma. When comparing radiotracer accumulation between primary tumors and metastases for the entire cohort, comparable SUVmax was recorded (P > 0.999), except for pulmonal findings (P = 0.013), indicative for uniform CXCR4 expression among TL. For higher IRS, a weak, but statistically significant correlation with increased SUVmax was observed (ρ = 0.328; P = 0.018). In 42/103 (40.8%) scans, more than five TL were recorded, with 12/42 (28.6%) exhibiting SUVmax above 10, suggesting eligibility for CXCR4-targeted treatment in this subcohort.ConclusionsIn a whole-body tumor read-out, a substantial portion of prevalent solid tumors demonstrated increased and uniform [68 Ga]Ga-pentixafor uptake, along with high image contrast. We also observed a respective link between in- and ex-vivo CXCR4 expression, suggesting high specificity of the PET agent. Last, a fraction of patients with [68 Ga]Ga-pentixafor-positive tumor burden were rendered potentially suitable for CXCR4-directed therapy.

1936P Targeted therapy of desmoplastic small round cell tumor guided by multilayered molecular profiling

1936P Targeted therapy of desmoplastic small round cell tumor guided by multilayered molecular profiling

The Role of Whole Abdomen and Pelvis Radiation Therapy in Desmoplastic Small Round Cell Tumor

Desmoplastic small round cell tumor (DSRCT) is a rare entity that typically presents in adolescent and young adult men with widespread abdominopelvic disease. The benefit of whole abdomen and pelvis radiation therapy (WAPRT) after chemotherapy and maximal surgical resection is unknown. Our objective was to evaluate the oncologic benefit and toxicity of WAPRT in this rare and aggressive disease. We conducteda retrospective review of patients with DSRCT treated at our institution primarily between 2018-2021. The cumulative incidence (CI) of intra-abdominopelvic failure was compared among those who received WAPRT after chemotherapy and surgery vs those who received chemotherapy and surgery alone without WAPRT utilizing Gray's method. Progression-free survival (PFS) and overall survival (OS) were also compared among patients who did and did not receive WAPRT using the Kaplan-Meier method from the date of surgery. Toxicity was graded per CTCAE v5.0 criteria. Twenty-eight patients were included (median age 17.5 years; range 6-38 years; 78% male, 22% female). All patients received chemotherapy with VDC/IE, all but one underwent extensive tumor resection, and all but two received HIPEC at time of resection. Nineteen patients (median age 13 years) received WAPRT after surgery, while 9 patients (median age 24 years) were treated with systemic therapy and surgery alone. Patients who received WAPRT were generally treated to 30 Gy in 20 fractions utilizing intensity-modulated radiation therapy (IMRT), with a boost to gross disease to a total dose of 45-50 Gy in 9 patients. Median follow up was 20 months. The CI of intra-abdominopelvic failure at 12 and 24 months was 16% and 50% with WAPRT vs 74% and 87% without WAPRT (p = 0.003), with a median time from surgery to intra-abdominopelvic failure of 15 months after WAPRT vs 5 months without. PFS was also improved with WAP-RT (94% and 83% at 12 and 24 months) vs without WAPRT (67% and 0% at 12 and 24 months), p = 0.001. Among those who received WAPRT, patients who received a boost to gross disease had similar intra-abdominopelvic control as those who had no gross disease to boost and received WAPRT only (CI at 24 months 50% without boost vs 48% with, p = 0.95). OS did not differ between those who did and did not receive WAPRT (OS at 24 months, 88% vs 83%, p = 0.89). Most toxicities after WAPRT were mild, including grade 1-2 fatigue, nausea, and vomiting, with the exception of one patient who developed veno-occlusive disease. Although limited by selection bias and short follow up, our study shows durable intra-abdominopelvic control and an improvement in PFS after WAPRT with IMRT, without an effect on OS. Additional larger, prospective investigations evaluating the value and toxicity of WAPRT for DSRCT are warranted.

Desmoplastic small round cell tumor with ovarian involvement on [18F]-FDG PET/CT

Desmoplastic small round cell tumor with ovarian involvement on [18F]-FDG PET/CT