EWSR1-fusion-negative, SMARCB1-deficient primary pulmonary myxoid sarcoma.

Primary pulmonary myxoid sarcoma (PPMS) is a recently defined rare neoplasm with histological and molecular similarity to extraskeletal myxoid chondrosarcoma. To date, 20 cases have been reported. A 48-year-old man presented with a huge mass filling the right hemithorax and extending into the tracheobronchial system. Histological findings were consistent with PPMS. Immunohistochemistry was positive for vimentin, CD10, and EMA, but other lineage-specific markers were negative. SMARCB1 (INI1) expression was lost in the tumour cells. FISH analysis (<i>EWSR1</i>, <i>FUS</i>, <i>NR4A3</i>, and <i>SMARCB1</i>) revealed no abnormalities. This case suggests SMARCB1 loss as a possible alternative molecular event driving EWSR1-negative PPMS.