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.

Prioritization of Novel Agents for Patients with Rhabdomyosarcoma: A Report from the Children's Oncology Group (COG) New Agents for Rhabdomyosarcoma Task Force.

Rhabdomyosarcoma is the most common soft tissue sarcoma diagnosed in children and adolescents. Patients that are diagnosed with advanced or relapsed disease have exceptionally poor outcomes. The Children's Oncology Group (COG) convened a rhabdomyosarcoma new agent task force in 2020 to systematically evaluate novel agents for inclusion in phase 2 or phase 3 clinical trials for patients diagnosed with rhabdomyosarcoma, following a similar effort for Ewing sarcoma. The task force was comprised of clinicians and basic scientists who collectively identified new agents for evaluation and prioritization in clinical trial testing. Here, we report the work of the task force including the framework upon which the decisions were rendered and review the top classes of agents that were discussed. Representative agents include poly-ADP-ribose polymerase (PARP) inhibitors in combination with cytotoxic agents, mitogen-activated protein kinase (MEK) inhibitors in combination with type 1 insulin-like growth factor receptor (IGFR1) inhibitors, histone deacetylase (HDAC) inhibitors, and novel cytotoxic agents.

Advances in the Diagnosis and Management of Neonatal Sarcomas.

Neonatal sarcomas comprise a heterogeneous group of rare soft tissue neoplasms that present unique diagnostic and therapeutic challenges. Recent advances in molecular profiling have improved diagnostic capabilities and reveal novel therapeutic targets. Clinical trials demonstrate differences in behavior between sarcoma subtypes that allow for better clinical management. Surgical resection has been replaced with a multimodal approach that includes chemotherapy and radiotherapy. Despite these advances, neonates with sarcoma continue to fare worse than histologically similar sarcomas in older children, likely reflecting differences in tumor biology and the complexities of neonatal medicine. This review focuses on recent advances in managing neonatal sarcomas.

More Than Meets the Eye? A Cautionary Tale of Malignant Ectomesenchymoma Treated as Low-risk Orbital Rhabdomyosarcoma.

Malignant ectomesenchymoma (MEM) is a rare multiphenotypic tumor comprised of mesenchymal and neuroectodermal components. MEM is typically diagnosed in infants and younger children and outcomes are variable. The current approach for treating MEM includes targeting the more aggressive mesenchymal component of the tumor, which is often rhabdomyosarcoma. Here, we describe a case of an orbital tumor initially diagnosed and treated as low-risk rhabdomyosarcoma. Local failure prompting a second biopsy revealed neuronal differentiation consistent with a diagnosis of MEM. Intensifying therapy and local radiotherapy led to a long-term cure. This case offers a cautionary tale that while outcomes for MEM were similar to matched rhabdomyosarcoma cohorts when treated on conventional Intergroup Rhabdomyosarcoma Study Group (IRSG) III/IV protocols, treating MEM using a decreased intensity low-risk rhabdomyosarcoma regimen may not be sufficient.

A method to culture human alveolar rhabdomyosarcoma cell lines as rhabdospheres demonstrates an enrichment in stemness and Notch signaling.

The development of three-dimensional cell culture techniques has allowed cancer researchers to study the stemness properties of cancer cells in in vitro culture. However, a method to grow PAX3-FOXO1 fusion-positive rhabdomyosarcoma (FP-RMS), an aggressive soft tissue sarcoma of childhood, has to date not been reported, hampering efforts to identify the dysregulated signaling pathways that underlie FP-RMS stemness. Here, we first examine the expression of canonical stem cell markers in human RMS tumors and cell lines. We then describe a method to grow FP-RMS cell lines as rhabdospheres and demonstrate that these spheres are enriched in expression of canonical stemness factors as well as Notch signaling components. Specifically, FP-RMS rhabdospheres have increased expression of SOX2, POU5F1 (OCT4), and NANOG, and several receptors and transcriptional regulators in the Notch signaling pathway. FP-RMS rhabdospheres also exhibit functional stemness characteristics including multipotency, increased tumorigenicity in vivo, and chemoresistance. This method provides a novel practical tool to support research into FP-RMS stemness and chemoresistance signaling mechanisms.

Advances in the management of pediatric genitourinary rhabdomyosarcoma.

Recent clinical trials have revealed several unanticipated complexities in the optimal management of genitourinary rhabdomyosarcoma (RMS). Improvement in outcomes for low- and intermediate-risk RMS over the past several decades led to the design of clinical trials aimed at reducing acute and late toxicity from extirpative surgeries, conventional radiotherapy, and cytotoxic chemotherapy. Results from these studies are mixed and have illuminated areas where historical risk stratification strategies need refining. Although radiotherapy has now become the standard for local control for most patients with genitourinary RMS, recent studies are demonstrating that there may be opportunities to minimize radiation toxicity while maintaining acceptable failure-free survival. A reduction in cyclophosphamide exposure may benefit select low-risk RMS patients but recent results illustrate that decreasing therapy intensity for most genitourinary RMS patients will require careful consideration in future prospective trials. Finally, recent studies highlight differences in perspective between European and North American investigators regarding the optimal balance of increased local failure rates but less toxicity versus improved event-free survival at a cost of higher toxicity. This review focuses on the results from the most recent RMS clinical trials and discusses their implications for the management of pediatric genitourinary RMS.

RASSF4 is required for skeletal muscle differentiation.

RASSF4, a member of the classical RASSF family of scaffold proteins, is associated with alveolar rhabdomyosarcoma, an aggressive pediatric cancer of muscle histogenesis. However, the role of RASSF4 in normal myogenesis is unknown. We demonstrate here that RASSF4 is necessary for early in vitro myogenesis. Using primary human myoblasts, we show that RASSF4 expression is dramatically increased during in vitro myogenic differentiation, and conversely that RASSF4-deficient myoblasts cannot differentiate, potentially because of a lack of upregulation of myogenin. In microscopy studies, we show that RASSF4 protein co-localizes with proteins of the myogenic microtubule-organizing center (MTOC) both before and after myogenic differentiation. RASSF4-deficient cells subject to differentiation conditions demonstrate a lack of shape change, suggesting that RASSF4 plays a role in promoting microtubule reorganization and myoblast elongation. In biochemical studies of myotubes, RASSF4 associates with MST1, suggesting that RASSF4 signals to MST1 in the myogenic differentiation process. Expression of MST1 in myoblasts partially reversed the effect of RASSF4 knockdown on differentiation, suggesting that RASSF4 and MST1 coordinately support myogenic differentiation. These data show that RASSF4 is critical for the early steps of myogenic differentiation.

The Transcriptional Coactivator TAZ Is a Potent Mediator of Alveolar Rhabdomyosarcoma Tumorigenesis.

Purpose: Alveolar rhabdomyosarcoma (aRMS) is a childhood soft tissue sarcoma driven by the signature PAX3-FOXO1 (P3F) fusion gene. Five-year survival for aRMS is <50%, with no improvement in over 4 decades. Although the transcriptional coactivator TAZ is oncogenic in carcinomas, the role of TAZ in sarcomas is poorly understood. The aim of this study was to investigate the role of TAZ in P3F-aRMS tumorigenesis.Experimental Design: After determining from publicly available datasets that TAZ is upregulated in human aRMS transcriptomes, we evaluated whether TAZ is also upregulated in our myoblast-based model of P3F-initiated tumorigenesis, and performed IHC staining of 63 human aRMS samples from tissue microarrays. Using constitutive and inducible RNAi, we examined the impact of TAZ loss of function on aRMS oncogenic phenotypes in vitro and tumorigenesis in vivo Finally, we performed pharmacologic studies in aRMS cell lines using porphyrin compounds, which interfere with TAZ-TEAD transcriptional activity.Results: TAZ is upregulated in our P3F-initiated aRMS model, and aRMS cells and tumors have high nuclear TAZ expression. In vitro, TAZ suppression inhibits aRMS cell proliferation, induces apoptosis, supports myogenic differentiation, and reduces aRMS cell stemness. TAZ-deficient aRMS cells are enriched in G2-M phase of the cell cycle. In vivo, TAZ suppression attenuates aRMS xenograft tumor growth. Preclinical studies show decreased aRMS xenograft tumor growth with porphyrin compounds alone and in combination with vincristine.Conclusions: TAZ is oncogenic in aRMS sarcomagenesis. While P3F is currently not therapeutically tractable, targeting TAZ could be a promising novel approach in aRMS. Clin Cancer Res; 24(11); 2616-30. ©2018 AACR.

A Review: Molecular Aberrations within Hippo Signaling in Bone and Soft-Tissue Sarcomas.

The Hippo signaling pathway is an evolutionarily conserved developmental network vital for the regulation of organ size, tissue homeostasis, repair and regeneration, and cell fate. The Hippo pathway has also been shown to have tumor suppressor properties. Hippo transduction involves a series of kinases and scaffolding proteins that are intricately connected to proteins in developmental cascades and in the tissue microenvironment. This network governs the downstream Hippo transcriptional co-activators, YAP and TAZ, which bind to and activate the output of TEADs, as well as other transcription factors responsible for cellular proliferation, self-renewal, differentiation, and survival. Surprisingly, there are few oncogenic mutations within the core components of the Hippo pathway. Instead, dysregulated Hippo signaling is a versatile accomplice to commonly mutated cancer pathways. For example, YAP and TAZ can be activated by oncogenic signaling from other pathways, or serve as co-activators for classical oncogenes. Emerging evidence suggests that Hippo signaling couples cell density and cytoskeletal structural changes to morphogenic signals and conveys a mesenchymal phenotype. While much of Hippo biology has been described in epithelial cell systems, it is clear that dysregulated Hippo signaling also contributes to malignancies of mesenchymal origin. This review will summarize the known molecular alterations within the Hippo pathway in sarcomas and highlight how several pharmacologic compounds have shown activity in modulating Hippo components, providing proof-of-principle that Hippo signaling may be harnessed for therapeutic application in sarcomas.

Absolute lymphocyte counts as prognostic indicators for immune thrombocytopenia outcomes in children.

BACKGROUND: Recent studies reviewing immune mechanisms of immune thrombocytopenia (ITP) have suggested acute and chronic forms may represent distinct immunopathological disorders. This study evaluated absolute lymphocyte counts (ALCs) as predictors for ITP outcomes. PROCEDURE: CBCs with differential counts were ascertained at presentation, 3, 6, and 12 months for 204 patients. Receiver operating characteristic (ROC) curves were used to determine cutoff values. Logistic regression models and recursive partitioning were used to evaluate which variables were significantly associated with outcomes. RESULTS: ALC values at presentation were not independently predictive of disease duration. However, ALC values at 3 months were significant predictors. Sixty-eight percent (40/59) of patients >8 years of age and 43% (20/46) of patients ≤ 8 years who had an ALC ≤ 3,000/µl at 3 months developed chronic ITP. This compares to chronic rates of only 25% (3/12) and 2% (2/87) of patients >8 and ≤ 8 years, respectively, with an ALC > 3,000/µl at 3 months. Further, 92% (60/65) of patients who developed chronic ITP had a 3-month ALC ≤ 3,000/µl. An ALC > 3,000/µl at 3 months is a strong predictor for platelet recovery as only 5% (5/99) of these patients developed chronic ITP. CONCLUSION: This study suggests progression to lower lymphocyte counts over the first few months of disease is a strong predictor for chronic ITP, allowing for risk stratification of patients, particularly when used in conjunction with other known predictors. Further research is needed to confirm these findings and to fully investigate the pathophysiological mechanisms responsible for this association.