However, Tie2-expressing monocytes (TEMs), a subpopulation of circulating, tumor-infiltrating myeloid cells with a highly proangiogenic phenotype, have been found in both humans and mice.12 Angiopoietin 2 (Ang-2), a Tie2 ligand, is overexpressed by ECs in tumors, further augmenting the ability of TEMs to stimulate angiogenesis through upregulation of proangiogenic enzymes, such as thymidine phosphorylase and cathepsin B.13, 14. This evidence concerns the gene TEK and neoplasm.