ROBO4 and cancer: Sets 4 and 5 contain genes typical of endothelial tissue, both actual angiogenic regulators TIE1/TIE2 (TEK), ARHGEF15, ROBO4, and ELTD1 and other endothelial markers such as CD34, CLEC14A, and ESAM. Several (7/12) of the genes in gene sets 4 and 5 were identified in the angiogenesis signature obtained from 1,250 tumors from different cancer types [36].