THE EFFECTS OF TOPICAL DEXAMETHASONE ON EXPERIMENTAL BRAIN-TUMORS ANDPERITUMORAL BRAIN EDEMA

To determine if topical dexamethasone administered to brain tumor beds would not only control peritumoral edema and suppress tumor growth bu t also prevent systemic steroid complications, we studied experimental brain tumors produced in 102 rabbits by implanted VX2 carcinoma cells . We separated 58 animals into three groups: 1) untreated rabbits (n = 15), 2) systemic dexamethasone-treated (4 mg/kg/day) rabbits (n = 18) , and 3) topical dexamethasone-treated (2.5 mul/h, osmotic pump) rabbi ts (n = 25). We administered systemic or topical dexamethasone from th e third day or from the seventh day after tumor implantation, and sacr ificed the animals on the 13th day. We compared survival in these thre e groups with that of another 44 rabbits, beginning treatment on the s eventh day. We measured brain water content in the white matter of the sacrificed rabbits by the specific gravity method. We measured the le ngth and width of the brain tumors of all the rabbits and estimated tu mor volume. Systemic and topical dexamethasone administered from the t hird day produced statistically significant inhibition of tumor volume as well as a mean reduction in peritumoral brain edema in most tested sites. Systemic and topical dexamethasone treatment resulted in a sta tistically significant increase in survival relative to the untreated group. These results suggest that topical dexamethasone is efficacious in a brain tumor model and its administration to brain tumor beds con stitutes a new therapeutic modality.