Synovial sarcoma: diagnosis on fine-needle aspiration by morphology and molecular analysis

Synovial sarcoma (SS) is characterized by the t(X; 18) (p11.2; q11.2) translocation resulting in the SYT-SSX fusion transcript, detectable by reverse transcriptase polymerase chain reaction (RT-PCR). Fine-needle aspiration (FNA) cytology diagnosis of SS is challenging. We evaluated the applicability of RT-PCR on FNAs and to perform a detailed cytomorphological analysis in unequivocal cases of SS.

A prospective and retrospective analysis was performed over 4 years (2003-2007). Prospectively, FNAs positive for the SYT-SSX fusion transcript by RT-PCR (n = 6) and, retrospectively, cases proven on histopathology and immunohistochemistry (ICC; positivity for vimentin and epithelial membrane antigen [EMA]/cytokeratin) as SS (n = 10) were included in the study. A detailed cytomorphological analysis was carried out.

There were 9 biphasic and 7 monophasic tumors. The aspirates from both biphasic and monophasic tumors were richly cellular in all cases with micro tissue fragments. Pericapillary arrangement of tumor cells was present in most cases. Attempted gland formation was seen in 7 of 9 biphasic tumors. The individual tumor cells were round, ovoid, or spindle shaped. Pleomorphism was mild; monophasic tumors displayed lesser pleomorphism as compared with the biphasic ones. Nuclear chromatin was bland in all cases except 1 and nucleolar prominence was seen in just 3 biphasic tumors. Mast cells were seen in 3 biphasic and 2 monophasic tumors. Scanty to moderate extracellular matrix material was seen in 5 cases.

FNA cytology of SS shows a spectrum of cytomorphological features; the diagnosis is confirmed by RT-PCR on the aspirated material for the SYT-SSX fusion transcript.