[Two cases of a solitary fibrous tumor with different growth patterns]

We report two cases of a solitary fibrous tumor demonstrating different growth patterns. Case 1: a 46-year-old male presented with a pedunculated solid tumor which was found between the lobes projecting from the lingula lobe. Case 2: a 68-year-old female demonstrated a tumor, measuring 2 cm in size, clearly inside the lung. The tumor was covered with pleura and could be removed bluntly. Histopathologically, spindle shaped fibroblasts were uniformly distributed in abundant, tangled collagen fibers in both cases. Sinusoid-like lumens, lined with one endothelium layer were also found. Immunohistological staining was strongly positive for vimentin and CD34, while it was negative for keratin, cytokeratin and EMA. The diagnosis of a pedunculated solitary fibrous tumor which extruded to outside the lung was made in one case, while in the other case a solitary fibrous tumor proliferating inside the lung was diagnosed. Many investigators have suggested this type of tumor to derive from mesenchymal tissue under mesothelium cells and is thus probably different from diffuse mesothelioma.