Histopathologic changes of thymoma preoperatively treated with corticosteroids

Preoperative treatment of thymoma in advanced stages with corticosteroids m ay reduce the size of the tumor, but no precise histologic evaluation has b een performed. We examined the histopathologic features of pretreatment bio psy and posttreatment surgical specimens of eleven cases of thymoma with su ch treatment to see the changes of the histologic subtypes based on Muller- Hermelink classification. All specimens were also assessed immunohistochemi cally for MIB-1 labeling and apoptotic cells to verify the effectiveness of this pretreatment. Seven tumors clinically diminished in size after the tr eatment with corticosteroids. Fungal infection occurred in three cases post operatively. The histology of mixed thymomas (two cases) was converted to t hat of medullary thymoma. Predominantly cortical thymomas (four cases) and cortical thymomas (three cases) changed to show similar histologic features ; both became epithelial-rich thymoma with large polygonal tumor cells havi ng indistinct cell borders. In contrast, two well-differentiated thymic car cinomas showed at surgery more prominent squamoid appearance with distinct cell borders. The apoptotic indices of epithelial cells were increased (P=0 .001), and the MIB-1 indices tended to be decreased with corticosteroid tre atment. These results su est that there may be a histogenetic relationship between medullary and mixed thymomas and also between predominantly cortica l and cortical thymomas. Corticosteroids may cause degenerative changes in the epithelial cells and lymphocytes and, in thymomas in advanced stages, c orticosteroid pretreatment may be warranted, although attention should be p aid to infection after surgery.