A 77-year-old woman presented with hoarseness and hemoptysis. Chest CT scan revealed a mediastinal tumor in the lumen of the left pulmonary artery. A definitive diagnosis could not be made based on mediastinoscopy and thoracotomy. Eight months later, multiple nodular shadows appeared in both lung fields.Video-assisted lung biopsy showed that these nodules were lung metastases of a spindle cell sarcoma. Based on the pathological and radiological findings, a pulmonary artery sarcoma was eventually diagnosed. Interestingly, on immunohistological staining, the tumor cells were diffusely positive for KIT, which is an immunohistochemical marker of gastrointestinal stromal tumors. The patient was treated with imatinib, a KIT tyrosine kinase inhibitor; however, the tumors progressed. The relationship between pulmonary artery sarcoma and KIT requires further study.