The (epi)genetics of human synovial sarcoma

Development and Validation of Prognostic Characteristics Associated With Chromatin Remodeling-Related Genes in Ovarian Cancer

BACKGROUND

Ovarian cancer (OC) is a prevalent malignant tumor in the field of gynecology, exhibiting the third highest incidence rate and the highest mortality rate among gynecological tumors. Chromatin remodeling accomplishes specific chromatin condensation at distinct genomic loci and plays an essential role in epigenetic regulation associated with various processes related to cancer development.

METHODS

Differentially expressed genes (DEGs) between OC and control samples were screened from The Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases, combined with chromatin remodeling-related genes (CRRGs) obtained from the GeneCards database to identify differentially expressed CRRGs (DECRRGs). Enrichment analysis and protein-protein interaction (PPI) network were performed on the DECRRGs. Prognostic genes of OC were screened using univariate Cox and least absolute shrinkage and selection operator (Lasso) analyses. A risk model based on prognostic genes was developed, and the survival probability of OC patients in different risk groups was analyzed by Kaplan-Meier (KM) curve. Finally, the expression levels of prognostic genes were validated by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting.

RESULTS

In total, 7 potential prognostic genes associated with the progression of OC patients were obtained, including ARID1B, ATRX, CHRAC1, HDAC1, INO80, MBD2, and SS18. Based on the expression level of prognostic genes, OC patients were divided into high-risk group and low-risk group. Survival analysis indicated that patients classified into the high-risk group had higher mortality rates, which enables this prediction model to be utilized as an independent predictor of OC. Immunocorrelation analysis showed that low-risk patients were more likely to benefit from immunotherapy.

CONCLUSION

In this study, we have identified 7 prognostic genes, including ARID1B, ATRX, CHRAC1, HDAC1, INO80, MBD2, and SS18. Overall, our findings provided a foundation for further comprehension of the potential molecular mechanisms underlying OC pathogenesis and progression.

Molecular Profiling Defines Three Subtypes of Synovial Sarcoma

Synovial Sarcomas (SS) are characterized by the presence of the SS18::SSX fusion gene, which protein product induce chromatin changes through remodeling of the BAF complex. To elucidate the genomic events that drive phenotypic diversity in SS, we performed RNA and targeted DNA sequencing on 91 tumors from 55 patients. Our results were verified by proteomic analysis, public gene expression cohorts and single-cell RNA sequencing. Transcriptome profiling identified three distinct SS subtypes resembling the known histological subtypes: SS subtype I and was characterized by hyperproliferation, evasion of immune detection and a poor prognosis. SS subtype II and was dominated by a vascular-stromal component and had a significantly better outcome. SS Subtype III was characterized by biphasic differentiation, increased genomic complexity and immune suppression mediated by checkpoint inhibition, and poor prognosis despite good responses to neoadjuvant therapy. Chromosomal abnormalities were an independent significant risk factor for metastasis. KRT8 was identified as a key component for epithelial differentiation in biphasic tumors, potentially controlled by OVOL1 regulation. Our findings explain the histological grounds for SS classification and indicate that a significantly larger proportion of patients have high risk tumors (corresponding to SS subtype I) than previously believed.

Genetic and Molecular Heterogeneity of Synovial Sarcoma and Associated Challenges in Therapy

Synovial sarcoma (SS) is one of the most common types of pediatric soft tissue sarcoma (STS) being far less frequent in adults. This STS type is characterized by one specific chromosomal translocation SS18-SSX and the associated changes in signaling. However, other genetic and epigenetic abnormalities in SS do not necessarily include SS18-SSX-related events, but abnormalities are more sporadic and do not correlate well with the prognosis and response to therapy. Currently, targeted therapy for synovial sarcoma includes a limited range of drugs, and surgical resection is the mainstay treatment for localized cancer with adjuvant or neoadjuvant chemotherapy and radiotherapy. Understanding the molecular characteristics of synovial sarcoma subtypes is becoming increasingly important for detecting new potential targets and developing innovative therapies. Novel approaches to treating synovial sarcoma include immune-based therapies (such as TCR-T cell therapy to NY-ESO-1, MAGE4, PRAME or using immune checkpoint inhibitors), epigenetic modifiers (HDAC inhibitors, EZH2 inhibitors, BRD disruptors), as well as novel or repurposed receptor tyrosine kinase inhibitors. In the presented review, we aimed to summarize the genetic and epigenetic landscape of SS as well as to find out the potential niches for the development of novel diagnostics and therapies.

Combination of HDAC and FYN inhibitors in synovial sarcoma treatment

The SS18-SSX fusion protein is an oncogenic driver in synovial sarcoma. At the molecular level, SS18-SSX functions as both an activator and a repressor to coordinate transcription of different genes responsible for tumorigenesis. Here, we identify the proto-oncogene FYN as a new SS18-SSX target gene and examine its relation to synovial sarcoma therapy. FYN is a tyrosine kinase that promotes cancer growth, metastasis and therapeutic resistance, but SS18-SSX appears to negatively regulate FYN expression in synovial sarcoma cells. Using both genetic and histone deacetylase inhibitor (HDACi)-based pharmacologic approaches, we show that suppression of SS18-SSX leads to FYN reactivation. In support of this notion, we find that blockade of FYN activity synergistically enhances HDACi action to reduce synovial sarcoma cell proliferation and migration. Our results support a role for FYN in attenuation of anti-cancer activity upon inhibition of SS18-SSX function and demonstrate the feasibility of targeting FYN to improve the effectiveness of HDACi treatment against synovial sarcoma.

SWI/SNF (BAF) complexes: From framework to a functional role in endothelial mechanotransduction

Endothelial cells (ECs) are constantly subjected to an array of mechanical cues, especially shear stress, due to their luminal placement in the blood vessels. Blood flow can regulate various aspects of endothelial biology and pathophysiology by regulating the endothelial processes at the transcriptomic, proteomic, miRNomic, metabolomics, and epigenomic levels. ECs sense, respond, and adapt to altered blood flow patterns and shear profiles by specialized mechanisms of mechanosensing and mechanotransduction, resulting in qualitative and quantitative differences in their gene expression. Chromatin-regulatory proteins can regulate transcriptional activation by modifying the organization of nucleosomes at promoters, enhancers, silencers, insulators, and locus control regions. Recent research efforts have illustrated that SWI/SNF (SWItch/Sucrose Non-Fermentable) or BRG1/BRM-associated factor (BAF) complex regulates DNA accessibility and chromatin structure. Since the discovery, the gene-regulatory mechanisms of the BAF complex associated with chromatin remodeling have been intensively studied to investigate its role in diverse disease phenotypes. Thus far, it is evident that (1) the SWI/SNF complex broadly regulates the activity of transcriptional enhancers to control lineage-specific differentiation and (2) mutations in the BAF complex proteins lead to developmental disorders and cancers. It is unclear if blood flow can modulate the activity of SWI/SNF complex to regulate EC differentiation and reprogramming. This review emphasizes the integrative role of SWI/SNF complex from a structural and functional standpoint with a special reference to cardiovascular diseases (CVDs). The review also highlights how regulation of this complex by blood flow can lead to the discovery of new therapeutic interventions for the treatment of endothelial dysfunction in vascular diseases.

Unmasking BCL-2 Addiction in Synovial Sarcoma by Overcoming Low NOXA

Simple Summary

Synovial sarcoma is a soft-tissue sarcoma that lacks effective systemic therapy and carries poor prognosis due to frequent late local recurrence and metastases. The cancer is known to be driven in part by increased expression of the pro-survival protein BCL-2. Surprisingly, synovial sarcoma proved resistant to BCL-2 inhibitors in pre-clinical trials. We identified increased activity of a second pro-survival protein, MCL-1, as responsible for this resistance. We showed that co-targeting both BCL-2 and MCL-1 proves to be an effective therapeutic approach both in cell culture and animal models of synovial sarcoma, supporting translation into clinical trials.

Abstract

Synovial sarcoma (SS) is frequently diagnosed in teenagers and young adults and continues to be treated with polychemotherapy with variable success. The SS18-SSX gene fusion is pathognomonic for the disease, and high expression of the anti-apoptotic BCL-2 pathologically supports the diagnosis. As the oncogenic SS18-SSX fusion gene itself is not druggable, BCL-2 inhibitor-based therapies are an appealing therapeutic opportunity. Venetoclax, an FDA-approved BCL-2 inhibitor that is revolutionizing care in some BCL-2-expressing hematological cancers, affords an intriguing therapeutic possibility to treat SS. In addition, there are now dozens of venetoclax-based combination therapies in clinical trials in hematological cancers, attributing to the limited toxicity of venetoclax. However, preclinical studies of venetoclax in SS have demonstrated an unexpected ineffectiveness. In this study, we analyzed the response of SS to venetoclax and the underlying BCL-2 family biology in an effort to understand venetoclax treatment failure and find a therapeutic strategy to sensitize SS to venetoclax. We found remarkably depressed levels of the endogenous MCL-1 inhibitor, NOXA, in SS compared to other sarcomas. Expressing NOXA led to sensitization to venetoclax, as did the addition of the MCL-1 BH3 mimetic, S63845. Importantly, the venetoclax/S63845 combination induced tumor regressions in SS patient-derived xenograft (PDX) models. As a very close analog of S63845 (S64315) is now in clinical trials with venetoclax in AML (NCT03672695), the combination of MCL-1 BH3 mimetics and venetoclax should be considered for SS patients as a new therapy.

Synovial Sarcoma: A Complex Disease with Multifaceted Signaling and Epigenetic Landscapes

PURPOSE OF REVIEW

Aside from a characteristic SS18-SSX translocation identified in almost all cases, no genetic anomalies have been reliably isolated yet to drive the pathogenesis of synovial sarcoma. In the following review, we explore the structural units of wild-type SS18 and SSX, particularly as they relate to the transcriptional alterations and cellular pathway changes imposed by SS18-SSX.

RECENT FINDINGS

Native SS18 and SSX contribute recognizable domains to the SS18-SSX chimeric proteins, which inflict transcriptional and epigenetic changes through selective protein interactions involving the SWI/SNF and Polycomb chromatin remodeling complexes. Multiple oncogenic and developmental pathways become altered, collectively reprogramming the cellular origin of synovial sarcoma and promoting its malignant transformation. Synovial sarcoma is characterized by complex epigenetic and signaling landscapes. Identifying the operational pathways and concomitant genetic changes induced by SS18-SSX fusions could help develop tailored therapeutic strategies to ultimately improve disease control and patient survivorship.

Identification of Novel Fusion Genes in Bone and Soft Tissue Sarcoma and Their Implication in the Generation of a Mouse Model

Fusion genes induced by chromosomal aberrations are common mutations causally associated with bone and soft tissue sarcomas (BSTS). These fusions are usually disease type-specific, and identification of the fusion genes greatly helps in making precise diagnoses and determining therapeutic directions. However, there are limitations in detecting unknown fusion genes or rare fusion variants when using standard fusion gene detection techniques, such as reverse transcription-polymerase chain reaction (RT-PCR) and fluorescence in situ hybridization (FISH). In the present study, we have identified 19 novel fusion genes using target RNA sequencing (RNA-seq) in 55 cases of round or spindle cell sarcomas in which no fusion genes were detected by RT-PCR. Subsequent analysis using Sanger sequencing confirmed that seven out of 19 novel fusion genes would produce functional fusion proteins. Seven fusion genes detected in this study affect signal transduction and are ideal targets of small molecule inhibitors. YWHAE-NTRK3 expression in mouse embryonic mesenchymal cells (eMCs) induced spindle cell sarcoma, and the tumor was sensitive to the TRK inhibitor LOXO-101 both in vitro and in vivo. The combination of target RNA-seq and generation of an ex vivo mouse model expressing novel fusions provides important information both for sarcoma biology and the appropriate diagnosis of BSTS.

SMARCB1-deficient Tumors of Childhood: A Practical Guide

The SMARCB1 gene ( INI1, BAF47) is a member of the SWItch/Sucrose Non-Fermentable (SWI/SNF) chromatin remodeling complex, involved in the epigenetic regulation of gene transcription. SMARCB1 acts as a tumor suppressor gene, and loss of function of both alleles gives rise to SMARCB1-deficient tumors. The prototypical SMARCB1-deficient tumor is the malignant rhabdoid tumor (MRT) which was first described in the kidney but also occurs in soft tissue, viscera, and the brain (where it is referred to as atypical teratoid rhabdoid tumor or AT/RT). These are overwhelmingly tumors of the very young, and most follow an aggressive and ultimately lethal course. Morphologically, most but not all contain a population of "rhabdoid" cells, which are large cells with abundant cytoplasm, perinuclear spherical inclusions, and eccentric vesicular nuclei with large inclusion-like nucleoli. MRT immunohistochemistry reveals complete loss of SMARCB1 nuclear expression, and molecular analysis confirms biallelic SMARCB1 inactivation in the vast majority. Rare AT/RTs have loss of SMARCA4, another SWI/SNF member, rather than SMARCB1. With the widespread adoption of SMARCB1 immunohistochemistry, an increasing number of SMARCB1-deficient tumors outside of the MRT-AT/RT spectrum have been described. In addition to MRT and AT/RT, pediatric tumors with complete loss of SMARCB1 expression include cribriform neuroepithelial tumor, renal medullary carcinoma, and epithelioid sarcoma. Tumors with variable loss of SMARCB1 expression include subsets of epithelioid malignant peripheral nerve sheath tumor, schwannomas arising in schwannomatosis, subsets of chordomas, myoepithelial carcinomas, and sinonasal carcinomas. Variable and reduced expression of SMARCB1 is characteristic of synovial sarcoma. In this review, the historical background, clinical characteristics, morphology, immunohistochemical features, and molecular genetics most germane to these tumors are summarized. In addition, familial occurrence of these tumors (the rhabdoid tumor predisposition syndrome) is discussed. It is hoped that this review may provide practical guidance to pathologists encountering tumors that have altered expression of SMARCB1.

Targeted therapies for soft-tissue sarcomas

The past several decades have revealed certain challenges that are inherent to soft-tissue sarcomas with regards to devising, testing and setting treatment paradigms for such a rare and heterogeneous malignancy. Despite this, significant advances have been made through the efforts of scientists, clinicians and patients alike. We are now entering a molecular era of cancer and current biotechnology is beginning to unravel the pathogenic enigma of these often devastating tumors. As our understanding of these malignancies improves, so does our list of potential treatment options. The impetus now lies with the medical/scientific community to direct translational research and subsequently the development and clinical testing of novel compounds in a fashion that best serves this unique patient population. To do so, we must continue to integrate the lessons of the past with the resources and promise of the future. This review will outline current areas of therapeutic interest in soft-tissue sarcomas with regard to agents that have reached clinical testing.

Truncated SSX protein suppresses synovial sarcoma cell proliferation by inhibiting the localization of SS18-SSX fusion protein

Synovial sarcoma is a relatively rare high-grade soft tissue sarcoma that often develops in the limbs of young people and induces the lung and the lymph node metastasis resulting in poor prognosis. In patients with synovial sarcoma, specific chromosomal translocation of t(X; 18) (p11.2;q11.2) is observed, and SS18-SSX fusion protein expressed by this translocation is reported to be associated with pathogenesis. However, role of the fusion protein in the pathogenesis of synovial sarcoma has not yet been completely clarified. In this study, we focused on the localization patterns of SS18-SSX fusion protein. We constructed expression plasmids coding for the full length SS18-SSX, the truncated SS18 moiety (tSS18) and the truncated SSX moiety (tSSX) of SS18-SSX, tagged with fluorescent proteins. These plasmids were transfected in synovial sarcoma SYO-1 cells and we observed the expression of these proteins using a fluorescence microscope. The SS18-SSX fusion protein showed a characteristic speckle pattern in the nucleus. However, when SS18-SSX was co-expressed with tSSX, localization of SS18-SSX changed from speckle patterns to the diffused pattern similar to the localization pattern of tSSX and SSX. Furthermore, cell proliferation and colony formation of synovial sarcoma SYO-1 and YaFuSS cells were suppressed by exogenous tSSX expression. Our results suggest that the characteristic speckle localization pattern of SS18-SSX is strongly involved in the tumorigenesis through the SSX moiety of the SS18-SSX fusion protein. These findings could be applied to further understand the pathogenic mechanisms, and towards the development of molecular targeting approach for synovial sarcoma.

Ectopic production of human chorionic gonadotropin by synovial sarcoma of the hip

BACKGROUND

Human chorionic gonadotropin (hCG) is a marker of pregnancy and a tumor marker for some gynecologic malignancies, including germ cell tumors and gestational trophoblastic neoplasia. Rarely, hCG is secreted by nongynecologic tumors, confounding the diagnosis.

CASE

A 45-year-old woman was evaluated for a persistently elevated β-hCG. Diagnosis of her primary malignancy, synovial sarcoma of the hip, was delayed as more common etiologies were considered, including ectopic pregnancy and gestational trophoblastic neoplasm. The workup eventually led to the diagnosis using imaging studies but ultimately resulted in a 3-month delay and unnecessary medical and surgical treatments.

CONCLUSION

This case highlights the importance of nongynecologic malignancies when evaluating patients with a persistent β-hCG.

Poorly differentiated synovial sarcoma is associated with high expression of enhancer of zeste homologue 2 (EZH2)

Background

Enhancer of zeste homologue 2 (EZH2) is a polycomb group (PcG) family protein. Acting as a histone methyltransferase it plays crucial roles in maintaining epigenetic stem cell signature, while its deregulation leads to tumor development. EZH2 overexpression is commonly associated with poor prognosis in a variety of tumor types including carcinomas, lymphomas and soft tissue sarcomas. However, although the synovial sarcoma fusion proteins SYT-SSX1/2/4 are known to interact with PcG members, the diagnostic and prognostic significance of EZH2 expression in synovial sarcoma has not yet been investigated. Also, literature data are equivocal on the correlation between EZH2 expression and the abundance of trimethylated histone 3 lysine 27 (H3K27me3) motifs in tumors.

Methods

Immunohistochemical stains of EZH2, H3K27me3, and Ki-67 were performed on tissue microarrays containing cores from 6 poorly differentiated, 39 monophasic and 10 biphasic synovial sarcomas, and evaluated by pre-established scoring criteria. Results of the three immunostainings were compared, and differences were sought between the histological subtypes as well as patient groups defined by gender, age, tumor location, the presence of distant metastasis, and the type of fusion gene. The relationship between EZH2 expression and survival was plotted on a Kaplan-Meier curve.

Results

High expression of EZH2 mRNA and protein was specifically detected in the poorly differentiated subtype. EZH2 scores were found to correlate with those of Ki-67 and H3K27me3. Cases with high EZH2 score were characterized by larger tumor size (≥ 5cm), distant metastasis, and poor prognosis. Even in the monophasic and biphasic subtypes, higher expression of EZH2 was associated with higher proliferation rate, larger tumor size, and the risk of developing distant metastasis. In these histological groups, EZH2 was superior to Ki-67 in predicting metastatic disease.

Conclusions

High expression of EZH2 helps to distinguish poorly differentiated synovial sarcoma from the monophasic and biphasic subtypes, and it is associated with unfavorable clinical outcome. Importantly, high EZH2 expression is predictive of developing distant metastasis even in the better-differentiated subtypes. EZH2 overexpression in synovial sarcoma is correlated with high H3K27 trimethylation. Thus, along with other epigenetic regulators, EZH2 may be a future therapeutic target.

Synovial sarcoma of the buttocks presenting with a non-healing wound and rapid progression after local resection: a case report

Synovial sarcoma is a malignant mesenchymal neoplasm that is frequently misdiagnosed as a benign condition because of its small size, slow growth, and well-delineated appearance. Rapid spread and early death occur rarely. Here we report a case of synovial sarcoma of the buttocks presenting with a non-healing wound and rapid progression after local resection in a 23-year-old woman. She initially found a slightly painful subcutaneous mass in the left buttock and underwent local excision. Postoperatively, she developed a non-healing wound that did not respond to conventional antibiotic therapy and local wound care, and pitting edema of the lower extremities. A magnetic resonance imaging scan revealed a large heterogeneous, irregular mass in the buttocks with regional lymph node involvement. Histological and immunohistochemical analyses suggested the diagnosis of a poorly differentiated synovial sarcoma. Her condition deteriorated dramatically shortly thereafter; she developed systemic edema and died of respiratory failure. This case suggests that synovial sarcoma may be fatal within months of recognition if improperly managed and stresses the importance of adequate pre-surgical evaluation and postoperative pathological analysis in the management of a subcutaneous mass.

Epigenetic and epigenomic mechanisms shape sarcoma and other mesenchymal tumor pathogenesis

Sarcomas comprise a large number of rare, histogenetically heterogeneous, mesenchymal tumors. Cancers such as Ewing's sarcoma, liposarcoma, rhabdomyosarcoma and synovial sarcoma can be generated by the transduction of mesenchymal stem cell progenitors with sarcoma-pathognomonic oncogenic fusions, a neoplastic transformation process accompanied by profound locus-specific and pangenomic epigenetic alterations. The epigenetic activities of histone-modifying and chromatin-remodeling enzymes such as SUV39H1/KMT1A, EZH2/KMT6A and BMI1 are central to epigenetic-regulated transformation, a property we coin oncoepigenic. Sarcoma-specific oncoepigenic aberrations modulate critical signaling pathways that control cell growth and differentiation including several miRNAs, Wnt, PI3K/AKT, Sav-RASSF1-Hpo and regulators of the G1 and G2/M checkpoints of the cell cycle. Herein an overview of the current knowledge of this rapidly evolving field that will undoubtedly uncover additional oncoepigenic mechanisms and yield druggable targets in the near future is discussed.

Targeting epigenetic misregulation in synovial sarcoma

Like many sarcomas, synovial sarcoma is driven by a characteristic oncogenic transcription factor fusion, SS18-SSX. In this issue of Cancer Cell, Su et al. elucidate the protein partners necessary for target gene misregulation and demonstrate a direct effect of histone deacetylase inhibitors on the SS18-SSX complex composition, expression misregulation, and apoptosis.

Cancer/testis (CT) antigens, carcinogenesis and spermatogenesis

During spermatogenesis, spermatogonial stem cells, undifferentiated and differentiated spermatogonia, spermatocytes, spermatids and spermatozoa all express specific antigens, yet the functions of many of these antigens remain unexplored. Studies in the past three decades have shown that many of these transiently expressed genes in developing germ cells are proto-oncogenes and oncogenes, which are expressed only in the testis and various types of cancers in humans and rodents. As such, these antigens are designated cancer/testis antigens (CT antigens). Since the early 1980s, about 70 families of CT antigens have been identified with over 140 members are known to date. Due to their restricted expression in the testis and in various tumors in humans, they have been used as the target of immunotherapy. Multiple clinical trials at different phases are now being conducted with some promising results. Interestingly, in a significant number of cancer patients, antibodies against some of these CT antigens were detected in their sera. However, antibodies against these CT antigens in humans under normal physiological conditions have yet to be reported even though many of these antigens are residing outside of the blood-testis barrier (BTB), such as in the basal compartment of the seminiferous epithelium and in the stem cell niche in the testis. In this review, we summarize latest findings in the field regarding several selected CT antigens which may be intimately related to spermatogenesis due to their unusual restricted expression during different discrete events of spermatogenesis, such as cell cycle progression, meiosis and spermiogenesis. This information should be helpful to investigators in the field to study the roles of these oncogenes in spermatogenesis.

Management of monophasic synovial sarcoma of the small intestine

Although prognosis for patients with intraabdominal synovial sarcoma is poor, laparoscopic wide regional excision may allow for a more prolonged disease-free survival.

Background:

Reports of primary intraabdominal synovial sarcomas are extremely rare.

Methods:

A literature review using PubMed was performed. A retrospective review of the one known case at our institution was completed.

Results:

Even the most experienced pathologists report that synovial sarcomas can be very difficult to diagnose correctly. One cytogenic abnormality that is common (>90%) and pathognomonic for synovial sarcoma is a characteristic chromosomal translocation resulting in the SYT/SSX fusion gene. Wide regional excision has been performed for intraabdominal sarcoma, with improved results. Our patient is more than 24 months with no evidence of recurrent or metastatic disease.

Conclusions:

The prognosis for patients with intraabdominal synovial sarcoma remains poor. However, wide regional excision may allow for prolonged disease-free survival.

Translating gene expression into clinical care: sarcomas as a paradigm

Whereas most solid tumors are characterized by considerable genetic instability and molecular heterogeneity, sarcomas include many subtypes with very specific underlying molecular events driving oncogenesis. Gene expression profiling and other modern techniques have consequently had particular success in identifying the critical biologic pathways active in specific sarcomas, yielding insights which can be translated into useful diagnostic biomarkers. Public availability of data sets and new sequencing-based technologies will accelerate this process. Molecular studies have also identified oncogenic pathways of particular importance in sarcomas which can be targeted by investigational drugs. Examples include histone deacetylases in translocation-associated sarcomas of young adults, Akt/mammalian target of rapamycin in pleomorphic sarcomas, and macrophage colony-stimulating factor in tenosynovial giant cell tumor. Despite challenges in organization and accrual, future clinical trials of sarcomas need to be designed that take into account specific molecular subtypes as distinct diseases.

Cryptic SYT/SXX1 fusion gene in high-grade biphasic synovial sarcoma with unique complex rearrangement and extensive BCL2 overexpression

Synovial sarcomas are high-grade malignant mesenchymal tumors that account for 10% of all soft-tissue sarcomas. Almost 95% of these tumors are characterized by a nonrandom chromosomal abnormality, t(X;18)(p11.2;q11.2), that is observed in both biphasic and monophasic variants. In this article, we present the case of a 57-year-old woman diagnosed with high-grade biphasic synovial sarcoma in which conventional cytogenetic analysis revealed the constant presence of a unique t(18;22)(q12;q13), in addition to trisomy 8. The rearrangement was confirmed by fluorescence in situ hybridization. The use of the whole chromosome painting probes WCPX did not detect any rearrangements involving chromosome X, although reverse-transcriptase polymerase chain reaction (PCR) analysis demonstrated the conspicuous presence of a SYT/SXX1 fusion gene. Spectral karyotyping (SKY) was also performed and revealed an insertion of material from chromosome 18 into one of the X chromosomes at position Xp11.2. Thus, the karyotype was subsequently interpreted as 47,X,der(X)ins(X;18)(p11.2;q11.2q11.2),der(18)del(18)(q11.2q11.2)t(18;22)(q12;q13),der(22)t(18;22). Real-time PCR analysis of BCL2 expression in the tumor sample showed a 433-fold increase. This rare finding exemplifies that thorough molecular-cytogenetic analyses are required to elucidate complex and/or cryptic tumor-specific translocations.

Frequent methylation of RASSF1A in synovial sarcoma and the anti-tumor effects of 5-aza-2'-deoxycytidine against synovial sarcoma cell lines

PURPOSE

In this study, the methylation status of RASSF1A in synovial sarcomas and the effect of demethylation on synovial sarcoma were examined.

METHODS

The methylation status in 74 soft tissue sarcomas (STSs) including 21 synovial sarcomas was determined by methylation specific PCR. The effect of the de-methylating agent 5-aza-20-deoxycytidine (5-Aza-dC) on synovial sarcoma was examined using synovial sarcoma cell lines (SYO-1 and HS-SY-II).

RESULTS

RASSF1A methylation was observed in 10 (47.6%) of 21 synovial sarcomas and in 10 (18.9%) of 53 the other STSs (P = 0.0295). De-methylation of the cells by treatment with 5-Aza-dC induced re-expression of RASSF1A and growth suppression of the cells. The calculated IC50 of 5-Aza-dC against the SYO-1 and the HS-SYII cells were 0.9 and 1.3 lM (96 h), respectively. With twice weekly administration of 1 or 10 mg/kg 5-Aza-dC, the growth of the mouse xenograft tumors of SYO-1 was significantly suppressed in comparison to the controls (P\0.01).

CONCLUSION

This is the first report showing the anti-tumor effect of 5-Aza-dC on synovial sarcoma. 5-Aza-dC is suggested to have a good therapeutic potential against synovial sarcoma.

Epigenetic features of human mesenchymal stem cells determine their permissiveness for induction of relevant transcriptional changes by SYT-SSX1

BACKGROUND

A characteristic SYT-SSX fusion gene resulting from the chromosomal translocation t(X;18)(p11;q11) is detectable in almost all synovial sarcomas, a malignant soft tissue tumor widely believed to originate from as yet unidentified pluripotent stem cells. The resulting fusion protein has no DNA binding motifs but possesses protein-protein interaction domains that are believed to mediate association with chromatin remodeling complexes. Despite recent advances in the identification of molecules that interact with SYT-SSX and with the corresponding wild type SYT and SSX proteins, the mechanisms whereby the SYT-SSX might contribute to neoplastic transformation remain unclear. Epigenetic deregulation has been suggested to be one possible mechanism.

METHODOLOGY/PRINCIPAL FINDINGS

We addressed the effect of SYT/SSX expression on the transcriptome of four independent isolates of primary human bone marrow mesenchymal stem cells (hMSC). We observed transcriptional changes similar to the gene expression signature of synovial sarcoma, principally involving genes whose regulation is linked to epigenetic factors, including imprinted genes, genes with transcription start sites within a CpG island and chromatin related genes. Single population analysis revealed hMSC isolate-specific transcriptional changes involving genes that are important for biological functions of stem cells as well as genes that are considered to be molecular markers of synovial sarcoma including IGF2, EPHRINS, and BCL2. Methylation status analysis of sequences at the H19/IGF2 imprinted locus indicated that distinct epigenetic features characterize hMSC populations and condition the transcriptional effects of SYT-SSX expression.

CONCLUSIONS/SIGNIFICANCE

Our observations suggest that epigenetic features may define the cellular microenvironment in which SYT-SSX displays its functional effects.

Molecular genetics of sarcomas: applications to diagnoses and therapy

Sarcomas are mesenchymal cancers consisting of tumors with various clinical and pathological features. Some of them compel affected individuals to lose important musculoskeletal functions, and some of them are highly malignant and life-threatening. A great amount of genetic information for sarcomas has accumulated during the past two decades, contributing diagnoses and treatments. From the standpoint of molecular genetics, sarcomas are classified into two groups: those with defined genetic alterations and those with various genetic alterations. The genetic alterations in the first group include reciprocal translocations resulting in fusion oncoproteins and oncogenic mutations of defined genes such as those of the c-kit gene in gastrointestinal stromal tumors. The function of fusion proteins includes transcription regulator, signal transducer, chromatic remodeling factor, and growth factor, some of which are suitable targets for the molecular therapy. In tumors belonging to the second group, the number of which is far larger than those of the first group, considerable genetic heterogeneity was found even among tumors with same pathological diagnosis. The disruption of the RB and p53 pathways was frequently found, resulting in the dysregulation of cell cycle and the genomic instability. The application of molecular target therapy for tumors in this group requires novel strategies to overcome cross talk between different signal pathways. Recent evidence from in vitro and in vivo experiments has indicated that the cells of origin of sarcomas are tissue stem cells such as mesenchymal stem cells, and the application of stem cell biology holds the promise of novel treatment options.

Poorly differentiated synovial sarcoma of the vagina: a case report and a clinical literature review

Synovial sarcomas (SS) account for 5–10% of soft-tissue sarcomas and typically arise in the para-articular regions of adolescents and young adults. Nonetheless, SS can occasionally occur in other regions of the body. Here, we present a first clinical literature report of a patient with an SS arising from the vaginal wall. A 40-year-old patient who presented a necrotic polypoid lesion, measuring 50 mm and extending from the external urethral meatus to the middle part of the anterior vaginal wall. The biopsy showed a poorly differentiated SS with abundant necrosis and a SYT-SSX1 mutation. A staging CT scan was negative for distant metastases. The patient, prior to the radical surgery, received neoadjuvant chemotherapy (ifosfamide and epirubicin) for three cycles. She underwent post-operative external radiotherapy and brachytherapy (50 Gy) due to close margins (<1 mm) in the pathologic specimen. She relapsed 11 and 16 months later with lung metastases, which, both times, were successfully removed by surgical resection. At 24 months from diagnosis, the patient is alive without further evidence of disease. In summary, in the presence of unfavourable prognostic factors, neoadjuvant chemotherapy could be the primary approach to reduce the tumour size and the risk of distant micro-metastases allowing a less aggressive radical surgery if the tumour is located in a non-extremity site. Hence, a multidisciplinary approach, if not influencing overall survival and disease-free survival, may improve the quality of life. In fact, in our patient we obtained a complete clinical control in the pelvis, avoiding pelvic exenteration with neoadjuvant chemotherapy.

Histone deacetylase inhibitors reverse SS18-SSX-mediated polycomb silencing of the tumor suppressor early growth response 1 in synovial sarcoma

Synovial sarcoma is a soft tissue malignancy characterized by the fusion of SS18 to either SSX1, SSX2, or SSX4 genes. SS18 and SSX are transcriptional cofactors involved in activation and repression of gene transcription, respectively. SS18 interacts with SWI/SNF, whereas SSX associates with the polycomb chromatin remodeling complex. Thus, fusion of these two proteins brings together two opposing effects on gene expression and chromatin structure. Recent studies have shown that a significant number of genes are down-regulated by the SS18-SSX fusion protein and that the clinically applicable histone deacetylase (HDAC) inhibitor romidepsin inhibits synovial sarcoma growth. Therefore, we set out to identify direct targets of SS18-SSX among genes down-regulated in synovial sarcoma and investigated if romidepsin can specifically counteract SS18-SSX-mediated transcriptional dysregulation. Here, we report that the tumor suppressor early growth response 1 (EGR1) is repressed by the SS18-SSX protein through a direct association with the EGR1 promoter. This SS18-SSX binding correlates with trimethylation of Lys(27) of histone H3 (H3K27-M3) and recruitment of polycomb group proteins to this promoter. In addition, we found that romidepsin treatment reverts these modifications and reactivates EGR1 expression in synovial sarcoma cell models. Our data implicate polycomb-mediated epigenetic gene repression as a mechanism of oncogenesis in synovial sarcoma. Furthermore, our work highlights a possible mechanism behind the efficacy of a clinically applicable HDAC inhibitor in synovial sarcoma treatment.

Modeling synovial sarcoma: timing is everything

Synovial sarcoma is characterized by the presence of a fusion protein involving SYT and SSX2. In this issue of Cancer Cell, Haldar et al. have genetically engineered a mouse model of this disease. They show that expression of the SYT-SSX2 fusion gene yields a highly penetrant and representative model of human synovial sarcoma, but only if expression occurs in a particular biologic context. The mouse model will be a valuable resource for studying tumor biology but is also a striking example of how important understanding of normal tissue and developmental biology is to our understanding of cancer.

Sarcomas: genetics, signalling, and cellular origins. Part 2: TET-independent fusion proteins and receptor tyrosine kinase mutations

Although the mechanisms that underlie sarcoma development are still poorly understood, the identification of non-random chromosomal translocations and receptor tyrosine kinase mutations associated with defined sarcoma types has provided new insight into the pathogenesis of these tumours. In Part 1 of the review (J Pathol 2007;213:4-20), we addressed sarcomas that express fusion genes containing TET gene family products. Part 2 of the review summarizes our current understanding of the implications of fusion genes that do not contain TET family members in sarcoma development, as well as that of specific mutations in genes encoding receptor tyrosine kinases (RTKs). The final section will serve as a summary of both reviews and will attempt to provide a synthesis of some of the emerging principles of sarcomagenesis.