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[A case of desmoid tumor involving the posterior mediastinum].

A 36-year-old woman visited our department because of back pain. Chest CT showed the 35 x 20 mm mass to be located in the left posterior mediastinum. Neurogenic tumor or pulmonary sequestration was suspected. We followed the tumor for 2 years, chest CT revealed an increase in size. En bloc resection of the tumor was performed. The tumor originated in the posterior mediastinum, protruded into the thoracic cavity and adhered to the left lower lobe and invaded the diaphragm, measuring 65 x 50 x 25 mm in size. This tumor was diagnosed pathologically as desmoid tumor which showed proliferation of spindle shape cells with collagen fibers, but with no cytologic atypia or mitotic figures were present. The tumor was alpha smooth muscle actin-positive, vimentin-positive, CD34-negative. Desmoid tumor of the posterior mediastinum is very rare. Desmoid tumors grow infiltratively and the recurrence rate after operation is high. Therefore, long-term follow up will be necessary in this case, although the patient has been well for 10 months.