Due to the high bleeding risk (ie, vascularized mass, coagulation alteration), a core-needle biopsy (18-G) was performed under CT guidance. However, results of the pathologic study revealed only normal pleural tissue. Finally, a surgical approach (simple removal of the tumor by hemiclamshell thoracotomy) was used. Pleural decortication was performed, with no visual thoracic wall invasion after the procedure. The macroscopic study of the tumor samples showed a 20 × 17 × 12 cm tumor with pleural and muscular infiltration, weighing 2 kg (Fig 4). The tumor had well-defined margins, with a polylobulated shape and necrotic areas. Histologically, the tumor exhibited a transition from low- to high-grade spindle cell proliferation areas. The low-grade areas showed spindle cells, with relatively small hyperchromatic nuclei in a collagenous background (Fig 5A). However, the spindle cells of these areas were focally positive for S100 staining (Fig 5B). The higher grade areas showed necrosis (40%) and clear pleomorphic cells with focal giant cells (Fig 5C and 5D). These areas were negative for S100 staining. In the most cellular areas, 21 mitoses per 10 high-power fields were recorded. The rest of the immunohistochemical analysis showed wide positivity for CD34; results of desmin, smooth muscle actin, acid fibrillary glial protein, BCL-2, STAT6, cytokeratin, and TLE1 staining were negative. The Ki-67 proliferative index was 20%.