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Synovial sarcomas (SS) are infrequent and morphologically heterogeneous soft tissue sarcomas. The t(X;18)(p11.2;q11.2), which results in fusion of the SYT gene at 18q11 with the SSX1, SSX2, or (rarely) SSX4 gene is a primary genetic event in 90% of SS. To determine whether the t(X;18) present in the original tumor is maintained in its passages, a dual-color break-apart FISH assay for SYT gene disruption was performed in two tissue microarrays (TMA) comprising eight molecularly confirmed primary SSs and their xenografts, which were followed for several generations. A simplified scoring system was applied to the FISH results of the primary and xenotransplanted SS to classify the FISH data into distinct groups. SYT disruption was identified in all eight primary SS and in all their passages without any significant differences among them, despite wide variations in xenotransplantation time between the primary tumors and their xenografts. The TMA-based FISH assay demonstrated genetic stability related to SYT gene rearrangement in primary and xenografted SS.

This paper discusses the diversity of synovial sarcomas (SSs) [biphasic (BSS), monophasic fibrous (MFSS), and poorly differentiated (PDSS)] and tissue microarray (TMA) evaluation of the immunophenotypic and histological progression of SSs in nude mice using three TMAs comprising 11 primary SSs (8 MFSSs, 2 BSSs, and 1 PDSS) and their xenografts. BSS and MFSS progressively transformed to a similar undifferentiated phenotype with loss of glandular component in the xenografts. Epidermal growth factor receptor and SALL2 were expressed in primary tumors and xenografts. Enhanced bcl-2 and bax expression were noted in xenografts. Ki-67 overexpression in xenografts correlated with high mitotic index. Epithelial membrane antigen (EMA) and cytokeratin AE1/AE3 were detected in all original and xenografted SSs. Hierarchical clustering differentiated original MFSS and BSS, but their xenografts clustered together due to similar immunoexpression profile. Our study demonstrates definite phenotypic variability of BSS and MFSS in the xenografts. Differences in immunoexpression for various markers existed between primary tumor and xenografts but not between subtypes. Hierarchical clustering grouped TMA immunostaining data and confirmed immunophenotypic variability; however, it failed to reveal any immunophenotypic differences between SYT-SSX1 and SYT-SSX2 type tumors. Nonetheless, reverse-transcriptase-polymerase chain reaction detected SYT-SSX transcripts in all primary SSs and their xenografts, thereby demonstrating their genetic stability.

The c-KIT and the platelet-derived growth factor receptor alpha (PDGFRalpha) have been shown to be important for tumor growth and progression in several soft-tissue sarcomas, including synovial sarcomas (SSs). It has been suggested that these c-KIT-positive cases might benefit from a tyrosine kinase inhibitor therapy. In this study, we analyze a series of SSs to investigate the presence of c-KIT and PDGFRalpha mutations with the aim of selecting those for a more adequate and appropriate therapy. We analyzed fresh-frozen tissues from 12 SSs (8 primary tumors and 4 nude mice xenotransplants from primary tumors). RNA was extracted to identify the presence of the SYT-SSX gene fusion to confirm the SS diagnosis. Mutational analysis of exons 9, 11, 13, and 17 of c-KIT and exons 12 and 18 of PDGFRalpha was performed by direct sequencing. Immunohistochemical analysis of c-KIT, PDGFRalpha, and p-PDGFRalpha was also performed. All analyzed cases showed the presence of SYT-SSX gene fusion transcripts confirming the diagnosis of SS, 10 carried the SYT-SSX1 fusion, and 2 the SYT-SSX2. Immunohistochemical analysis showed expression of c-KIT in 3 cases in which no molecular alterations were detected. For the PDGFRalpha, we observed an in-frame deletion of codons 554 and 555 in a case which also showed a strong immunopositivity for the phosphorylated form of PDGFRalpha. PDGFRalpha expression was observed in 8 cases. We suggest that a more exhaustive mutational analysis of the c-KIT and PDGFRalpha genes should be performed to ascertain which cases would really benefit from a tyrosine kinase inhibitor therapy in SS.

Synovial sarcoma (SS) is a neoplasm that poses diagnostic problems, due to its histologic heterogeneity. The poorly differentiated variant, in particular, may be histologically indistinguishable from other small round cell tumors. Detection of the synovial sarcoma-associated t(X;18) or SYT-SSX fusion transcripts may be necessary to confirm the diagnosis of SS in difficult cases. Most of SS carry a t(X;18) in about one third of cases as the sole cytogenetic abnormality. We evaluated a case of poorly differentiated synovial sarcoma and their derived tumors in nude mice xenografts and cell cultures. We used a panel of antibodies (including those to intermediate filament, nerve-sheath associated markers, and neuronal and neuroectodermal related antigens) to better establish the immunophenotype, supported by the ultrastructural evaluation. The tumor exhibited the distinctive cytogenetic abnormality t(X;18), together with a der(1)t(1;22)(p36;q12). Present results show that this poorly differentiated synovial sarcoma not only expresses conventional biologic and genetical markers for SS but also neuroectodermal features when transplanted into nude mice and cultured in vitro.