Primary Pulmonary Myxoid Sarcoma with EWSR1::ATF1 Fusion: A Case Report.

Primary pulmonary myxoid sarcoma is a rare lung sarcoma, mostly involving the central lung and harboring the EWSR1::CREB1 fusion. We report an exceptional case of primary pulmonary myxoid sarcoma arising in the peripheral lung and harboring an EWSR1::ATF1 gene fusion. A 67-year-old man presented with a solid nodule in the right lower lobe, and wedge resection was performed. Microscopically, the tumor consisted of reticular proliferation of uniform mildly atypical spindle cells within abundant myxoid stroma. Immunohistochemically, smooth muscle actin was positive but desmin was negative. Fluorescence in situ hybridization confirmed EWSR1 and ATF1 gene rearrangements. No recurrence was seen for 12 months. Pathological findings and gene rearrangements are important for the diagnosis of primary pulmonary myxoid sarcoma. Complete resection and careful observation are required.