Preoperative treatment of
thymoma in advanced stages with
corticosteroids may reduce the size of the
tumor, but no precise histologic evaluation has been performed. We examined the histopathologic features of pretreatment biopsy and posttreatment surgical specimens of eleven cases of
thymoma with such treatment to see the changes of the histologic subtypes based on Muller-Hermelink classification. All specimens were also assessed immunohistochemically for MIB-1 labeling and apoptotic cells to verify the effectiveness of this pretreatment. Seven
tumors clinically diminished in size after the treatment with
corticosteroids.
Fungal infection occurred in three cases postoperatively. The histology of mixed
thymomas (two cases) was converted to that 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 having indistinct cell borders. In contrast, two well-differentiated
thymic carcinomas 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 treatment. These results suggest that there may be a histogenetic relationship between medullary and mixed
thymomas and also between predominantly cortical and cortical
thymomas.
Corticosteroids may cause degenerative changes in the epithelial cells and lymphocytes and, in
thymomas in advanced stages,
corticosteroid pretreatment may be warranted, although attention should be paid to
infection after surgery.