Malignant solitary fibrous tumor of the pleura with liposarcomatous differentiation.

Pleural solitary fibrous tumors (SFTs) are uncommon tumors. Although these tumors have been well characterized, malignant pleural SFTs with liposarcomatous differentiation have not been reported. We report an unusual malignant pleural SFT intermixed with foci of well-differentiated liposarcoma. The patient was a 66-year-old, white man with a large, solid right pleural mass that measured 13.5 x 10.3 x 8.5 cm. The tumor was composed of spindle-shaped and plump cells embedded in dense collagenous stroma. The tumor cells were arranged in interlacing fascicles or in a patternless pattern. Marked nuclear atypia, a high mitotic rate (21 mitoses per 10 high-power fields), and areas of prominent necrosis were evident. In addition, numerous adipocytes mixed with typical lipoblasts were seen scattered throughout portions of the tumor. Immunohistochemistry revealed the tumor cells were strongly positive for CD34 and vimentin and negative for cytokeratin, desmin, smooth muscle actin (IA4), and S100. To the best of our knowledge, this case represents the first example of a malignant SFT with liposarcomatous differentiation.