Increased numbers of endothelial cells are observed in peripheral blood of cancer patients. These circulating endothelial cells (CECs) may contribute to the formation of blood vessels in the tumor or reflect vascular damage caused by treatment or tumor growth. Characterization of these cells may aid in the understanding of the angiogenic process and may provide biomarkers for treatment efficacy of angiogenesis inhibitors. To identify markers typical for CECs in cancer patients, we assessed global gene expression profiles of CD146 immunomagnetically enriched CECs from healthy donors and patients with metastatic breast, colorectal, prostate, lung, and renal cancer. From the generated gene profiles, a list of 61 marker genes for CEC detection was generated, and their expression was measured by real-time quantitative PCR in blood samples from 81 metastatic cancer patients and 55 healthy donors that were immunomagnetically enriched for CECs. A set of 34 genes, among which novel CEC-associated genes, such as THBD, BST1, TIE1, POSTN1, SELE, SORT1, and DTR, were identified that were expressed at higher levels in cancer patients compared with healthy donors. Expression of the VWF, DTR, CDH5, TIE, and IGFBP7 genes were found to discriminate between cancer patients and "healthy" donors with a receiver operating characteristic curve accuracy of 0.93. Assessment of the expression of these genes may provide biomarkers to evaluate treatment efficacy.