A Giant Solitary Fibrous Tumor of the Pleura Exceeding 15 cm Classified as Low Risk: A Rare Case Report

Solitary fibrous tumors of the pleura (SFTPs) are rare mesenchymal neoplasms that are usually benign but may occasionally recur or undergo malignant transformation. Tumor size is an important prognostic factor; lesions larger than 10 cm are associated with recurrence and poor outcomes, and tumor size ≥15 cm is considered as a risk factor in prognostic models. Histologically, benign SFTPs of ≥15 cm in size are extremely uncommon.

A 48-year-old male presented with exertional dyspnea and chest tightness. Chest CT revealed a giant mediastinal mass measuring 138 × 91 × 129 mm. The encapsulated tumor originated from the pleura and was completely resected via a thoracotomy. Histological examination revealed spindle cells with hyalinization and calcification, without necrosis or mitotic figures. Immunohistochemical staining was positive for CD34 and STAT6, confirming a diagnosis of SFTP. The resected specimen measured 185 × 80 × 145 mm, with a low Ki-67 labeling index of 3%, and was classified as low risk according to the 4-variable Demicco risk stratification model.

We report a rare case of a histologically benign but giant SFTP exceeding 15 cm in diameter. Although classified as low risk, large tumor size itself may reflect biological aggressiveness and be associated with recurrence or malignant transformation. Therefore, careful long-term follow-up is required.