Tumor endothelial marker 7 (TEM7) was identified through serial analysis of gene expression on endothelial cells isolated from human normal and malignant colorectal tissues. Further experiments verified TEM7 was highly expressed in the endothelium of numerous other cancer types including breast, lung and brain tumors. At least four isoforms of TEM7 are known to exist; these include intracellular, secreted, and membrane-bound forms. A homologous protein, TEM7R (also known as PLXDC2), acts as a binding partner to TEM7 and is also abundantly expressed in the endothelium of malignant colorectal cancer but is absent or rare in normal colon mucosa. High expression of TEM7 is associated with metastasis and poor survival of patients with osteogenic sarcoma.