Solitary fibrous tumor (SFT) occurring at various extrapleural sites is sometimes difficult to diagnose because of its histologic variability. Although a solitary fibrous tumor is usually a slow-growing tumor with favorable prognosis, a small number of malignant cases have been reported. In the present study, we examined the clinical behavior, histologic, immunohistochemical and molecular features of 17 cases of extrapleural SFT. Four tumors were located in the pelvic cavity, two in the nasal cavity, two were confined to the pulmonary parenchyma, and there was one each in the meninges, kidney, mediastinum, retroperitoneum, temporal region, neck, groin, buttock and thigh. Histologically, all the tumors were characterized by the presence of areas consisting of a proliferation of bland spindle cells with variable amounts of thick, often hyalinized or keloid-like intercellular collagen bundles. Highly cellular areas were observed in three tumors, frequent mitoses in two, and cellular pleomorphism and tumor necrosis in one each. All 17 tumors showed immunoreactivity to CD34 and 15 (88%) to bcl-2 protein. The labeling indices of p53, mdm2 protein and Ki-67 were generally low. PCR-SSCP and a subsequent sequence analysis of the p53 gene disclosed point mutation at codon 161 in exon 5 in one of the 13 cases analyzed. According to follow-up information, none of the patients had developed local recurrence or distant metastasis. Our results suggest that most extrapleural SFTs behave in a benign fashion even in a higher histologic grade group, and it is difficult to predict their clinical outcome. Complete surgical excision in order to obtain clear margins and long-term follow-up is advisable for patients with an extrapleural SFT.

BACKGROUND Spindle and giant cell carcinomas of the lung are rare subtypes and are regarded as one type of lung carcinoma, termed pleomorphic carcinoma in the Armed Forces Institute of Pathology classification. This classification is different from the World Health Organization classification. METHODS Thirty‐seven cases of sarcomatoid (spindle and/or giant cell) carcinoma of the lung were studied by light microscopy, conventional histochemistry, and immunohistochemistry to establish their clinical and histologic characteristics. RESULTS The patient population was comprised of 29 men and 8 women ages 33–81 years. Seventeen patients died of their disease and there was no statistically significant difference in patient prognosis between sarcomatoid carcinoma and nonsarcomatoid carcinoma of the lung. Using light microscopy, 5 cases (13.5%) comprised entirely of sarcomatoid components without carcinomatous elements were classified as Group A. In the remaining 32 cases (86.5%), classified as Group B, carcinomatous components were present (adenocarcinoma [18 cases; 48.7%], squamous cell carcinoma [8 cases; 21.6%], and large cell carcinoma [6 cases; 16.2%]). Sarcomatoid components were divided further into three categories: spindle cell type, giant cell type, and mixed spindle and giant cell type. Immunohistochemically, the sarcomatoid components of all 37 cases were positive for cytokeratins. Statistically, there was no significant prognostic difference between the 37 cases of sarcomatoid carcinoma and 647 cases of nonsarcomatoid, nonsmall cell carcinoma of the lung (P = 0.8537). CONCLUSIONS The sarcomatoid portions in all sarcomatoid carcinomas in the current study showed an epithelial differentiation, and there was no apparent difference in biologic behavior between sarcomatoid carcinoma and ordinary lung carcinoma. Cancer 1999;86:608–16. © 1999 American Cancer Society.