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A poorly-differentiated form of synovial sarcoma has been recognized which shows greater degree of cellularity, anaplasia and increased mitotic activity than usual. It is not a distinct subtype but represents tumor progression in monophasic or biphasic synovial sarcoma and is seen in about 20% of cases of synovial sarcoma.
Microscopically, it consists of one of the following patterns: large epithelioid cells with abundant eosinophilic cytoplasm and prominent nucleoli; small cells with scant cytoplasm and resembling other small round blue cell tumors; or high-grade spindle cells with increased mitotic activity and necrosis. As expected, it is a highly aggressive tumor with great propensity for metastasis.
Microscopically, it consists of one of the following patterns: large epithelioid cells with abundant eosinophilic cytoplasm and prominent nucleoli; small cells with scant cytoplasm and resembling other small round blue cell tumors; or high-grade spindle cells with increased mitotic activity and necrosis. As expected, it is a highly aggressive tumor with great propensity for metastasis.