CD248, known also as endosialin and tumor endothelial marker 1 (TEM1), is a 95-kDa transmembrane glycoprotein expressed in activated stromal and perivascular fibroblasts and pericytes.  CD248 is an important regulator of critical pathways involved with stromal fibroblast migration, and proliferation.    During normal embryonic development, CD248 is highly expressed across diverse tissue types.  Postnatally, its expression is restricted to the endometrium, bone marrow and corpus luteum.  In vitro protein structure studies demonstrated interaction of the extracellular domain of CD248 with extracellular matrix proteins, facilitating cell migration and metastatic formation.  Conversely, the cytoplasmic domain was shown to regulate stromal fibroblast function.  CD248 is expressed within the endothelium across many tumor types include sarcomas, carcinoma and neuroectodermal tumors.  Within the tumor stroma, activated fibroblasts subpopulations are often associated with poor prognosis.