To enable monitoring of tumour angiogenesis during cancer progression, we implanted pre-oncogenic RT2 islets into Tie2-EYFP reporter mice, characterized by endothelial expression of the enhanced yellow fluorescent protein (EYFP), and obtained by crossing Tie2-Cre mice16 with R26R-EYFP(Ai3) mice17. This evidence concerns the gene TEK and cancer.