The underlying mechanism of the effect of steroid pulse therapy on thymoma.

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Glucocorticoid has been used in thymomas. However, the mechanism of steroid action on thymomas is not clear.We cultured sliced thymoma and infant thymus in glucocorticoid under HOS culture (high oxygen submersion culture).The reduction in tumor size was accompanied with a marked reduction in the CD4+8+ double positive immature thymocytes that expressed higher levels of glucocorticoid receptor. Apoptotic changes were observed in both neoplastic epithelial cell and lymphocyte components following glucocorticoid.We cultured thymoma in vitro under drugs, 5-fluoroucil(5-FU), cisplatin(CDDP), docertaxel(DOC), carboplatin(CBDCA), paclitaxel(PTX). Apoptotic changes were also observed in both neoplastic epithelial cell and lymphocyte.The efficiency of pre-operative steroid pulse therapy and chemotherapy in thymoma was most prominent which is probably related to the specific effect on GR rich CD4+8+ double positive immature lymphocytes which are abundant in this type of thymoma.We propose that steroid pulse therapy can be used as induction therapy for advanced thymoma, especially those rich in associated CD4+CD8+ double positive cells. Preoperative diagnosis of thymoma is essential for this treatment. Histological classification of thymoma using WHO classification and flow cytometric analysis of the lymphocytes associated with thymoma to determine the proportion of CD4+CD8+ double positive cells will predict the response to the steroid pulse therapy. Flow cytometric analysis oflymphocytes recovered from needle biopsy samples is a useful measure for this purpose.