The density of immature CD105-stained endothelial cells in the tumour decreased from 19.5±2.5 to 8.7±2.0 after treatment with imatinib (P=0.01), and the ratio of CD105- to CD31-stained (total) vessels was used as an indicator of vascular immaturity. The gene discussed is PECAM1; the disease is neoplasm.