Diagnosis: Intrapulmonary solitary fibrous tumor
• Solitary fibrous tumors (SFTs) are typically CD34 positive. Immunohistochemistry profile also includes bcl2 and CD99 reactivity, with no reactivity for cytokeratin, smooth muscle markers, S100, or CD31. SFTs are usually slow-growing tumors with potential for local spread and with malignant potential. They are generally pleural-based and sometimes on a pedicle; however, they can appear to be completely intrapulmonary.
• Criteria for malignancy include dense cellularity, necrosis, and mitotic rate. Larger tumors are more likely to display these criteria; however, tumors lacking these criteria can recur with invasive growth. The differential diagnosis includes other spindle cell neoplasms.
• . Bland SFTs, especially when they occur posterior and medial, can enter the differential diagnosis of schwannoma (nerve sheath tumors), and cellular SFT with atypia can enter the differential diagnosis with synovial sarcoma, sarcomatoid carcinomas, fibrosarcomas, and fibrous histiocytomas.
