A Case of a Malignant Solitary Fibrous Tumor of the Pleura Rapidly Enlarged 17 Years after Its Discovery

Abstract

Solitary fibrous tumor (SFT) is a relatively rare tumor derived from mesenchymal cells. We experienced a case of malignant SFT that increased rapidly in size 17 years after its initial detection. The case involved a 74-year-old man who had been detected to have a pleural nodule and an anterior mediastinal nodule 17 years earlier. He did not desire to receive therapy and had been followed until one year before when both lesions started to grow. Partial resection of the lung including the tumors was performed. Intraoperative findings showed that the pleural lesion was a tumor emerging from the lung parenchyma. Pathological analysis showed CD34 (+) spindle-shaped cells, nuclear atypia, mitotic figures, and high MIB-1 index. The diagnosis was malignant SFT arisen from the visceral pleura. The anterior mediastinal nodule was diagnosed as type A thymoma. The SFT in this case increased rapidly in size one year before the operation, and it was possible that the degree of malignancy might increase during the course. However, the diameter was relatively small and FDG accumulation was low. SFT is a slowly increasing tumor and the prognosis is often good, but 10-30% of them are malignant, and it is considered difficult to preoperatively distinguish between benign and malignant SFTs. Therefore, surgical resection may be considered when SFT is suspected.