Solitary fibrous tumor composing benign and malignant components in the floor of the mouth: A case report

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm arising mostly in the pleura. We describe a case of SFT composed of benign and malignant components in the left floor of the mouth of an 88-year-old man presenting with a growing mass. A biopsy was diagnostically inconclusive because immunohistochemical staining for CD34 was negative. Postoperatively, the resected tumor was found to comprise 2 components of different cellularity and atypia. Immunohistochemically, tumor cells in both components were positive for vimentin, bcl-2 and STAT6 but showed opposing immunoreactivity to CD34. The malignant lesion with hypercellularity and atypia contained several small necrotic foci was immunohistochemically negative for CD34, and exhibited a high Ki-67 labeling index. On the other hand, the benign lesion of hypocellularity and no atypia was positive for CD34. Taken together, these findings indicated a rare case of SFT with distinctive histological features of benign and malignant components.