Dedifferentiated Solitary Fibrous Tumor of Thoracic Cavity

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Solitary fibrous tumor (SFT) is a mesenchymal tumor characterized by fibroblast-like tumor cells, thick collagen bands, a hemangiopericytoma-like branching vascular pattern and CD34 expression of tumor cells. 1 Although some cases show malignant behavior, most of the cases are benign and have his-tologically bland-looking tumor cells. Rarely, highly pleomor-phic sarcoma arises within a primary or recurrent SFT having typical histologic features. This is a phenomenon similar to that seen in dedifferentiated liposarcoma. Dedifferentiated SFT (DSFT) is rare, with less than 30 cases reported worldwide, 2-6 and it has not been previously reported in Korea. Here, we present a case of DSFT. A 73-year-old male presented with dyspnea for one month. On computerized tomography, a large mass involving the left thoracic cavity and mediastinum was found (Fig. 1A). Sarcoma was suspected upon needle biopsy, based on the large size and mesenchymal features of the tumor cells. During surgery, a 30×25×20-cm-sized well-encapsulated multinodular solid tumor was found. The tumor was divided surgically into two parts and removed (Fig. 1B). Microscopically, the tumor was composed of fibroblast-like tumor cells, collagen fibers and many thin-walled blood vessels, which are characteristics of a SFT (Fig. 1C). The tumor cells were diffusely and strongly positive for CD34 (Fig. 1D) and showed moderate nuclear atypism in focal areas. The mitotic index was generally low, but it was up to 4/10 high-power fields (HPF) in a few areas. Necrosis was absent, and the diagnosis of SFT with malignant potential was made. After 38 months, a computerized tomography showed a 20-cm-sized recurrent mass involving the mediastinum and left thoracic cavity and a separate 4.5-cm-sized mass in the medias-tinum. The tumor appeared to have invaded rib bones. The tumor was divided surgically into several parts and removed along with three segments of rib bones (Fig. 2A). The larger mass was composed of highly pleomorphic spindle cells with a mitotic index up to 21/10 HPFs (Fig. 2B). It showed necrosis and invasion to rib bones. The tumor cells were nondistinctive and showed no muscular or osteoid differentiation. They were arranged in a storiform pattern in some areas and were negative for CD34, desmin, S-100, and CD99. Conversely, the smaller mass showed typical microscopic findings …