Title: Nieuwe prognostische en predictieve merkers voor geselecteerde sarcomen van de weke delen
Other Titles: New prognostic and predictive markers for selected soft tissue sarcomas
Authors: Przybyl, Joanna
Issue Date: 8-Oct-2013
Abstract: Soft tissue sarcomas (STS) comprise a heterogeneous group of malignant mesenchymal tumors that include more than 130 distinct diagnostic entities. They arise from various types of connective tissues, especially adipocytic tissue, muscles, nerves, deep skin fibroblasts, blood vessels, bones and cartilage. There is also a relatively large subgroup of sarcomas of uncertain origin. STS represent approximately 1% of all neoplasms in adults and more than 10% of neoplasms diagnosed in children. Many of STS subtypes harbor specific cytogenetic changes, such as chromosome translocations, gene point mutations and genomic copy number aberrations.These tumors are characterized by poor clinical outcome and the currently accepted clinical prognostic factors in STS do not accurately discriminate between low risk and high risk patients. Better understanding of STS biology is important to improve diagnosis, develop more reliable molecular prognostic and predictive factors, and to propose new potential therapeutic targets. Development of novel agents for targeted therapy is of special importance because many STS subtypes are resistant to conventional chemotherapy and the effective STS treatment options are limited. Moreover, the STS research is often circumscribed by the scarcity of samples available for analysis. It has been recently perceived that only for four STS subtypes the cytogenetic information is available for more than 100 cases and that for many STS subtypes only less than 10 cases have been analyzed.The first specific objective of this project was identification of new prognostic and predictive markers associated with long term survival of patients with synovial sarcomas (SynSa). Microarray technology (array CGH and gene expression microarrays) was applied to understand the biology of these tumors and to select genes which are differentially expressed in tumor tissues. Using a training/validation set strategy on collected 100 primary specimens from patients with long clinical follow-up, we tested the hypothesis that specific CINSARC (complexity index in sarcomas) gene expression signature predicts metastatic outcome in translocation-related sarcomas, as it does in non-translocation related sarcomas of the complex genotypes. We have also examined the prognostic significance of Genomic Index (GI), reflecting the complexity of genomic rearrangements in tumor specimens based on array CGH profile. We have demonstrated that both CINSARC gene signature and GI outperform current prognostic grading system and provide information that would influence the clinical decisions. Additionally, we pointed to the potentially predictive value of GI, especially in pediatric SynSa patients. The results of this collaborative study are described in Paper I.We performed the detection of SynSa specific fusion transcripts SS18-SSX1/2 in all cases examined for gene expression and genomic alterations, to confirm the diagnosis and provide additional molecular characteristics of patients included in this study. Application of RT-PCR allowed us to identify atypical fusion transcripts in three patients, which are depicted in Paper III. In this thesis, we described the first case with a complex translocation which involved another gene, i.e. REPS2 (RALBP1 associated Eps domain containing 2), located on the X chromosome at Xp22. This novel transcript variant was detected both in primary and metastatic specimens derived from the same patient. Apparently, this variant preserved the transforming function of the usual SS18-SSX1 fusion oncogene, which indicates that the mechanism of tumorigenesis in this case might have been similar as in other SynSa cases.In the second part of this project we intended to explore the hypothesis that the detection of circulating tumor cells (CTCs) in the peripheral blood (PB) can serve as a prognostic marker of the disease outcome in Ewing sarcoma (ES) patients. To reach this aim we evaluated ES specific fusion oncogenes (EWS-FLI1 and EWS-ERG) as markers of the presence of sarcoma cells in routinely collected PB specimens, and correlated these results with disease outcome. Moreover, we searched for the CTC markers alternative to already known fusion transcripts, basing on available gene expression profiling data. We tested the hypothesis that selected tissue specific markers can be used to detect metastatic cells in PB of ES patients. As presented in Paper II, the expression of typical EWS-FLI1/ERG fusion transcripts in the PB was found in two (6%) of patients, and the additional 76% of patients carried the unusual shorter in lenght EWS-FLI1 fusion transcripts, which may imply ES as a systemic disease. We have also observed the abnormal expression of CDH2 and CDT2 genes in the PB of a subset of ES patients, which significantly correlated with worse overall survival (OS). We suggest that combination of metastasis presence at diagnosis, a well-established clinical negative prognostic factor, with evaluation of CDH2 expression level, may predict poor prognosis in ES patients with the higher accuracy. This study demonstrates the prognostic value of molecular PB testing at the time of routine histopathological diagnosis.In the third part of this thesis (Paper IV) we aimed to identify genes involved in a recurrent t(X;17)(p11.2;q21.33) translocation identified in two independent low-grade endometrial stromal sarcoma (ESS) patients. We described the molecular characteristics of these tumors, by a combination of cytogenetic and molecular methods, microarrays and next-generation whole transcriptome sequencing. We identified MBTD1 (malignant brain tumor domain-containing 1) and CXorf67 (chromosome X open reading frame 67) as fusion partners involved in the novel reciprocal rearrangement. Gene expression profiling demonstrated that cases with MBTD1-CXorf67 transcript cluster together with the classical low-grade ESS cases carrying previously described JAZF1-associated fusions. In array CGH analysis, no genomic imbalances at the t(X;17) breakpoints were identified, indicating that MBTD1-CXorf67 is a balanced translocation. The chimeric fusion gene MBTD1-CXorf67 identifies yet another cytogenetically distinct subgroup of low-grade ESS and offers the opportunity to shed more light on the biological functions of the two poorly characterized genes.<w:latentstyles deflockedstate="false" defunhidewhenused="true" defsemihidden="true" defqformat="false" defpriority="99"  
Publication status: published
KU Leuven publication type: TH
Appears in Collections:Laboratory for Genetics of Malignant Disorders

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