RESULTS: All three patients (two women, one man, average age 41 years old) presented with dyspnea on exertion, two had chest tightness, and one had intermittent syncope. Computed tomography pulmonary angiography showed that two patients had filling defect in the main pulmonary artery, left and right pulmonary arteries, and one patient had filling defect in the right upper pulmonary artery. All patients were misdiagnosed as pulmonary thromboembolic disease and underwent surgery. Macroscopically, the PAS (with length of 5.0 cm-9.5 cm, diameter of 1.2 cm -4.5cm) appealed as mucoid intraluminal or nodular sessile mass spreading along the pulmonary artery. Microscopically, the tumor consisted of spindle cells with fascicular and storiform patterns and was accompanied by necrosis and stromal myxoid change. Immunohistochemically, vimentin, desmin and CD34 were highly positive, and α-smooth muscle actin (α-SMA) was slightly positive in one patient, and vimentin and α-SMA were highly positive in the other two patients. Intimal sarcoma was diagnosed in one patient, and leiomyosarcoma was diagnosed in the other two patients.