Lack of dexamethasone effect on the antitumor activity of cisplatin.

High-dose glucocorticosteroids have proven to be effective antiemetic agents when used before and after cisplatin chemotherapy. To rule out a possible decrease in cisplatin antitumor activity by a direct effect of short-term glucocorticosteroid treatment, survival was studied in mice inoculated with P388 leukemia and then treated with cisplatin preceded by a single high dose (1.5 mg/kg) of dexamethasone (Dex). The median survival of animals treated with cisplatin-Dex was 19 days, and that of animals treated with cisplatin alone was 18 days. These survival durations were significantly longer (P less than 0.01) than the survival time of the controls (median, 12 days). A double-layer soft agar clonogenic assay was used to study the possible effect of Dex on cisplatin inhibition of tumor colony-forming units from two human tumor cell lines (HEC-1A, endometrial; and WiDr, colon). In this model, the addition of Dex to cisplatin showed no statistically significant effect. These data suggest that Dex has no inhibitory effect on the antitumor activity of cisplatin.