TM4SF1 and cancer: Subsequently, we demonstrated that TM4SF1 is expressed at high levels in cultured endothelial cells originating from blood or lymphatic vessels [6,8], endothelial progenitor cells, and in bone marrow-derived mesenchymal stem cells [9], as well as in vivo in an endothelium undergoing pathological angiogenesis in both experimental models of angiogenesis in mice [6] and in human cancers [6,7].