Abstract: Background and purpose: Primary pulmonary myxoid sarcoma (PPMS) is a very rare lung tumor that has recently been shown to harbor EWSR1-CREB1 translocation. This study aimed to investigate the clinicopathological characteristics and differential diagnosis of PPMS. Methods: The clinical and pathological features of 6 cases of PPMS with EWSR1 gene rearrangement were reviewed. Immunohistochemistry and fluorescence in situ hybridization (FISH) study were performed. Results: Six patients were enrolled in this study, including 4 male patients and 2 female patients with an age range of 23 to 64 years (median age, 44 years). All tumors involved pulmonary parenchyma, with a predominant endobronchial component in 1 and adjacent to bronchus in 5 patients. Microscopically, the tumor was lobulated and composed of cords of polygonal, spindle cells within myxoid stroma. Tumors were immunoreactive for only Vimentin and weakly focal for epithelial membrane antigen (EMA). All tumors were shown to harbor EWSR1 gene rearrangement by FISH. Follow-up of all patients showed that 1 patient developed a pleura and bone metastasis but was still alive and 5 were disease-free after 4-29 months. Conclusion: PPMS is an extremely rare sarcoma with low- grade malignant potential. This is characterized by distinct histological features and EWSR1 gene rearrangement. It is important that understanding tumor spectrum and genetic feature can contribute to diagnosis and differential diagnosis of PPMS.

Key words: EWSR1 gene, Primary pulmonary myxoid sarcoma, Fluorescence in situ hybridization