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

AIMS: 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. METHODS AND RESULTS: 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. CONCLUSION: 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.