The vascular architecture of rat brain tissue was examined with anti-CD31 antibody, and dexamethasone treated tumor regions showed reduced vessel area (16.45±1.36 μm2) as compared to saline treated tumor regions (30.83±4.31 μm2, p<0.001) and non-tumor regions (22.80±1.11 μm2, p<0.01). The gene discussed is PECAM1; the disease is neoplasm.