SOLITARY FIBROUS TUMOR - CLINICOPATHOLOGICAL, IMMUNOHISTOCHEMICAL, AND ULTRASTRUCTURAL ANALYSIS OF 12 CASES ARISING IN SOFT-TISSUES, NASAL CAVITY AND NASOPHARYNX, URINARY-BLADDER AND PROSTATE

The clinicopathological features of 12 extraserosal solitary fibrous r umours (SFT) are described. The age of the patients ranged from Is to 72 years (mean: 48.2 years; median: 54 years); 5 were female patients. Seven lesions arose in soft tissue (5 in perifascial, and 1 each in s ubcutaneous and intramuscular tissues). They were situated in the groi n (2 cases) and the neck, right buttock, left scapula, upper arm, and anterior abdominal wall (1 case each). One polypoid lesion was seen in in the nasal cavity and 1 in the nasopharynx; 2 neoplasms arose in th e urinary bladder and 1 was located in the prostate and periprostatic tissue. Nine lesions were excised; in 1 patient wide excision was perf ormed and in 2 patients, transurethral resection. Limited follow-up of 3 cases revealed a benign clinical course. The size of the neoplasms ranged from 1.7 cm to 20.0 cm (mean: 5.4 cm; median: 3.5 cm). Histolog ically, the neoplasms were well circumscribed and composed of cytologi cally bland spindle cells arranged without an obvious pattern; focally storiform or fascicular growth patterns were seen. Tumour cells were separated by thick bands of collagen demonstrating foci of keloid-fike hyalinization. Prominent vascularity showing a haemangiopericytoma-li ke vascular pattern and vessels with thick, hyalinized vessel walls we re seen in all cases. Increased mitotic activity was noted in 2 soft t issue cases (4-6 mitoses in 10 high-power fields); the other cases sho wed fewer than 2 mitotic figures in 10 high-power fields. Immunohistoc hemically, all cases tested stained positively for vimentin, CD34 and CD99, and 2 cases showed focal myofibroblastic differentiation. Two ca ses examined ultrastructurally showed a fibroblastic phenotype; focall y pinocytic vesicles and microfilaments were identified. SFT represent s a distinct neoplasm that should be included in the differential diag nosis of spindle-cell neoplasms in soft tissue, nasal cavity and nasop harynx, urinary bladder, and prostate. Strict diagnostic criteria are necessary to avoid overdiagnosis or confusion with more aggressive neo plasms in these locations.