Cytomorphologic features of malignant solitary fibrous tumor with mediastinal involvement sampled by endoscopic and endobronchial ultrasound-guided fine-needle aspiration: A comparison of two cases.

Solitary fibrous tumor (SFT) is an uncommon fibroblastic neoplasm with considerable risk of local recurrence. SFT is histologically characterized by bland spindled-to-epithelioid cells in alternating hyper- and hypocellular zones, a "patternless pattern," ectatic "staghorn" vessels with variable edematous perivascular stroma, and thick ropey collagen. Cytologically, smears are variably cellular with spindled-to-epithelioid cells with oval nuclei, wispy cytoplasm, multiple inconspicuous nucleoli, and occasional nuclear pseudoinclusions.