Desmoplastic spindle cell thymomas: a clinicopathologic and immunohistochemical study of 14 cases

Fourteen cases of spindle cell thymoma with prominent desmoplastic changes are presented. The patients are 9 women and 5 men between the ages of 46 and 79 years. Clinically, the patients presented with symptoms of chest pain, shortness of breath, and dyspnea. Radiographic imaging showed the presence of an anterior mediastinal mass, and surgical resection of the tumor mass was accomplished in all of the cases. Grossly, all the tumors were described as ovoid tumor masses measuring between 4 and 9 cm in greatest dimension. At cut surface, the tumors were described as solid and light tan-brown in color. Necrosis and hemorrhage were not recorded in any of the cases. Histologically, 8 cases were invasive, and 6 were encapsulated tumors. Extensive areas of young fibrocollagen and a prominent fibroblastic proliferation characterized the tumors. Scattered areas of more conventional spindle cell thymoma were present in all cases but mitotic activity, necrosis, and/or hemorrhage were not identified. Immunohistochemical stains were performed in 9 cases, showing tumor cells positive for pancytokeratin, cytokeratin 5/6, Bcl-2, Pax8, and vimentin. Clinical follow-up in 8 patients showed that all are alive and well 1 to 8 years after diagnosis. The current growth pattern of spindle cell thymomas is unusual and should be kept in mind when evaluating mediastinoscopic biopsies.