An 84-year-old woman was transferredbecause of dyspnea. She had no past history or family history of sarcoma. Herrespiratory sounds were decreased, hypotension was observed, and blood gasanalysis showed hypoxemia. Both bilateral hilar lymphadenopathy and dilatedpulmonary artery were suspected on chest X-ray. On chest computed tomographyscan, the upper mediastinal space was occupied with low-density mass, whichspread from the pulmonary artery trunk to peripheral branches with phymatoidenlargement (Figure 1A). Although we treated the symptoms, the patient died ofrespiratory failure on the third hospital day. Postmortem examination revealed aremarkable dilatation of the pulmonary artery, and mucous tumors thatoriginated from the pulmonary artery trunk were observed (Figure 2A).Histologically, proliferation of undifferentiated fusiform tumor cells withatypical cylindroid nucleus was observed in the lumen of the pulmonary artery(Figure 2B). Immunohistochemical examination was positive for vimentin, a-SMA(smooth muscle actin), and HHF-35 (common muscle actin) (Figure 2C). These?ndings revealed the tumor was a pulmonary artery intimal sarcoma. Pulmonary artery sarcoma is a rare tumor ofthe great vessels. The diagnosis is usually made postoperatively or at autopsy.The average age at presentation is 48 years, with a slight female predominance(1). The most common symptom is dyspnea, followed by chest or back pain, cough,hemoptysis, and malaise (1). Computed tomography ?ndings include aheterogeneous tumoral attenuation resulting in a ?lling defect that primarilyinvolves the entire luminal diameter of the proximal pulmonary trunk, withvariable intravascular extension in one or both pulmonary arteries (2). Theprognosis is poor, and mean survival is 12-18 months (3). Surgical resectionhas been reported to decrease clinical symptoms and lengthen survival (4).Recently, the effectiveness of chemotherapy and radiotherapy have been reported(5). Figure 1. On the chest computed tomography scan, upper mediastinal space wasoccupied with low-density mass, which overcrowded from the pulmonary trunk toperipheral sites with phymatoid enlargement. Figure 2. (A) Postmortem examinationrevealed a remarkable dilatation of pulmonary artery and mucous tumors (*) thatoriginated from the pulmonary artery trunk. (B) Histologically, proliferationof undifferentiated fusiform tumor cells with atypical cylindroid nucleus wasobserved in the lumen of the pulmonary artery. (C) Immunohistochemicalexamination was positive for vimentin, a-SMA (smooth muscle actin), and HHF-35(common muscle actin).