Primary synovial sarcoma of the lung: report of two cases confirmed by molecular detection of SYT‐SSX fusion gene transcripts

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Abstract
Primary pulmonary sarcoma is rare, and frequently creates diagnostic challenges. We describe two cases of primary pulmonary spindle cell sarcoma in which a molecular approach using archival paraffin-embedded tissue was proved to aid diagnosis. Both patients had huge masses replacing the upper and middle lobes of the lung, respectively, without any primary extrapulmonary neoplastic lesions. Microscopically, the lesions showed a solid hypercellular nodular or lobular growth of atypical short spindle cells in variably intersecting fascicles or in a haphazard fashion, together with focal areas displaying a prominent haemangiopericytoma-like pattern. Immunohistochemically, a small number of the tumour cells were positive for epithelial markers such as cytokeratin and epithelial membrane antigen. In both cases, a reverse transcription-polymerase chain reaction using RNA extracted from formalin-fixed, paraffin-embedded tissues detected SYT-SSX fusion gene transcripts, which are characteristic of synovial sarcoma. On the basis of the morphological and molecular findings, these tumours are considered to be rare examples of monophasic synovial sarcoma of the lung. Our molecular assay detecting the SYT-SSX fusion transcripts is useful for the final diagnosis of synovial sarcoma arising at such an unusual anatomical site.