Release of circulating tumor cells and cell-free nucleic acids is an infrequent event in synovial sarcoma: liquid biopsy analysis of 15 patients diagnosed with synovial sarcoma.

BACKGROUND: Synovial sarcoma is a rare soft tissue tumor which contains the unique SS18-SSX1, SS18-SSX2 - or, rarely, SS18-SSX4 - fusion transcripts. It is well known that some soft tissue tumors, like Ewing sarcomas and myxoid liposarcomas, can spread via the blood with free circulating tumor cells (CTC); this can be detected by several sensitive molecular biology methods. Here we report a study of fifteen synovial sarcoma patients with varied clinical backgrounds. METHOD: After blood withdrawal and nucleic acid isolation, we attempted to detect the SS18-SSX fusion genes from circulating tumor cells or cell-free nucleic acids with nested PCR and droplet digital PCR. RESULTS: SS18-SSX2 fusion transcript was identified in a small copy number with droplet digital PCR in one case. Nested PCR could not detect any of the fusion transcripts in the examined 15 synovial sarcoma cases. CONCLUSIONS: Heretofore two case reports could detect CTCs in synovial sarcoma - in the first paper, the patient was diagnosed with poorly differentiated type while the other had a rare primary gastric synovial sarcoma. However, until now, no other studies have detected CTCs in the peripheral blood of synovial sarcoma patients. Based on our findings, we can conclude that detection of the chimeric SS18-SSX fusion gene after surgical excision and/or chemotherapy/radiotherapy is a rare circumstance and hence in itself is not sufficient for monitoring the tumor recurrence. Therefore, monitoring of other possible biomarkers - for example synovial sarcoma specific miRNAs - is recommended.

The oncomir face of microRNA-206: A permanent miR-206 transfection study.

MiR-206 is a remarkable miRNA because it functions as a suppressor miRNA in rhabdomyosarcoma while at the same time, as previously showed, it can act as an oncomiRNA in SMARCB1 immunonegative soft tissue sarcomas. The aim of this study was to investigate the effect of miR-206 on its several target genes in various human tumorous and normal cell lines. In the current work, we created miR-206-overexpressing cell lines (HT-1080, Caco2, iASC, and SS-iASC) using permanent transfection. mRNA expression of the target genes of miR-206 (SMARCB1, ACTL6A, CCND1, POLA1, NOTCH3, MET, and G6PD) and SMARCB1 protein expression were examined with quantitative real-time polymerase chain reaction, immunoblotting, immunocytochemistry, and flow cytometry. MiRNA inhibition was used to validate our results. We found a diverse silencing effect of miR-206 on its target genes. While an overall tendency of downregulation was noted, expression profiles of individual cell lines showed large variability. Only CCND1 and MET were consistently downregulated. MiR-206 had an antiproliferative effect on a normal human fibroblast cell line. A strong silencing effect of SMARCB1 in miR-206 transfected SS-iASC was most likely caused by the synergic influence of the SS18-SSX1 fusion protein and miR-206. In the same cell line, a moderate decrease of SMARCB1 protein expression could be observed with immunocytochemistry and flow cytometry. In the most comprehensive analysis of miR-206 effects so far, a modest but significant downregulation of miR-206 targets on the mRNA level was confirmed across all cell lines. However, the variability of the effect shows that the action of this miRNA is largely cell context-dependent. Our results also support the conception that the oncomiR effect of miR-206 on SMARCB1 plays an important but not exclusive role in SMARCB1 immunonegative soft tissue sarcomas so it can be considered important in planning the targeted therapy of these tumors in the future. Impact statement Mir-206 is a very unique microRNA because it can act as a suppressor miRNA or as an oncomiRNA depending on the tumor tissue. In SMARCB1 negative soft tissue sarcomas miR-206 is overexpressed, so thus in epithelioid and synovial sarcomas it functions as an oncomiRNA. MiR-206 has diverse silencing effects on its target genes. We found that the action of miR-206 is largely cell context dependent. The oncomiR role of miR-206 is crucial but not exclusive in SMARCB1 negative soft tissue sarcomas and miR-206 has an antiproliferative effect on a normal human fibroblast cell line. Expressions of miR-206 targets observed in tumors can only be reproduced in the corresponding tumorous cell lines. This is the first study which examined the permanent effect of miR-206 on its target genes in normal, tumor, and genetically engineered cell lines.

First cloned human immortalized adipose derived mesenchymal stem-cell line with chimeric SS18-SSX1 gene (SS-iASC).

The SS18-SSX chimeric gene is unique to synovial sarcoma. Multiple model systems including mouse cell lines expressing SS18-SSX, and genetically engineered mouse models of synovial sarcoma have been developed to elucidate the role of the chimeric gene in synovial sarcomagenesis. Although several cell lines stably expressing human SS18-SSX exist, there is an ongoing need for cell culture models enabling researchers to investigate the molecular mechanism of SS18-SSX action in a relevant cellular context. Here we report the establishment of a novel SS18-SSX1-expressing cell line created from immortalized human adipose tissue-derived mesenchymal stem cells via lentiviral transduction of the chimeric gene. Our cell line, termed SS-iASC, has been characterized by karyotyping and cell line identification, and stable expression of SS18-SSX1 has been verified using real-time PCR (RT-PCR), nested PCR, immunofluorescence, and immunoblotting. Focal cytokeratin positivity characteristic of synovial sarcoma but no ß-Catenin, Bcl-2 or cyclin D1 expression was observed in SS-iASC. The novel cell line expressing SS18-SSX1 on a human adipose-derived stromal cell background is expected to be helpful in addressing the question whether the chimeric gene alone is sufficient to trigger the formation of synovial sarcoma.

Unusual Signal Patterns of Break-apart FISH Probes Used in the Diagnosis of Soft Tissue Sarcomas.

Break-apart FISH probes are the most popular and reliable type of FISH probes used to confirm certain pathological diagnoses. The interpretation is usually easy, however, in some instances it is not so unequivocal. Our aim was to reveal and elucidate the problems occurring in the process of evaluation of the break-apart probe results. Altogether 301 soft tissue sarcomas with confirmed molecular tests using break-apart probes were assessed to reveal the frequency and type of unusual signal pattern. Among 89 synovial sarcoma (SS18) 11%, 12 alveolar rhabdomyosarcoma (FOXO1) 50%, 53 myxoid liposarcoma (DDIT3) 7.5%, 6 low grade fibromyxoid sarcoma (FUS) 67%, 93 Ewing sarcoma (EWSR1) 3%, 12 clear cell sarcoma (EWSR1) 8%, 5 desmoplastic small round cell tumor (EWSR1) 0%, 9 extraskeletal myxoid chondrosarcoma (EWSR1) 0%, 2 myoepithelial carcinoma (EWSR1) 50%, 14 dermatofibrosarcoma protuberans (COL1A1) 86% and 6 nodular fasciitis (USP6) 17% atypical break-apart signals were detected. Despite the unusual signal pattern type, the fusion genes were detected using either metaphase FISH, interphase FISH with translocation/TriCheck probe or RT-PCR methods. Although the interpretation problems in the process to evaluate the break-apart probe results is well known from sporadic case reports, a systemic overview to detect their frequency has not been performed so far. In our work we highlighted the relative frequency of this problem and pinpointed those signal-patterns which, despite their unusual appearance, can still confirm the diagnosis.