TM4SF1 and neoplasm: TM4SF1 regulates biological and cellular activities through its ability to form 100–300 nm diameter protein complexes called TMEDs (TM4SF1-enriched microdomains) on the surfaces of cells that express high levels of TM4SF1 in vitro [6,7,8,9] and the tumor endothelium of human cancers in vivo [7].