Metastatic poorly differentiated monophasic synovial sarcoma to lung with unknown primary: a molecular genetic analysis.

Poorly differentiated synovial sarcomas are diagnostically challenging soft tissue tumors. They can be indistinguishable from other "small blue cell tumors" based on morphology and even immunohistochemical studies. Here we report a rare case of poorly differentiated metastatic synovial sarcoma to lung without known primary, diagnosed with molecular genetic analysis. The tumor was negative for EMA and cytokeratin, previously reported as the most sensitive immunostaining markers for synovial sarcomas. SYT-SSX gene fusion, characteristic for synovial sarcoma, was identified in this case by FISH and RT-PCR assays.