RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is a novel tumoreassociated antigen expressed in human uterine and ovarian carcinomas. The predicted amino acid sequence of RCAS1 (213 a.a.) possesses an N-terminal transmembrane region and a coiled-coil structure in the C-terminal portion, indicating that RCAS1 is a type II membrane protein able to form oligomers through the coiled-coil structure. RCAS1 revealed different expression pattern from the known tumore associated antigens such as, YH206, GA733, CA125, CEA and sialyl Le molecules in human tumore cell lines. Recent study indicated RCAS1 acts as a ligand for a putative receptor present on various human cells including T, B and NK cells. RCAS1 inhibited the in vitro growth of receptor-expressing cells and induced apoptosis. It was suggested that tumore cells might evade immune surveillance by expression of RCAS1.Synonyms: Cancer-associated surface antigen RCAS1, EB9, Estrogen receptor-binding fragment-associated gene 9 protein, PDAF, Receptor-binding cancer antigen expressed on SiSo cells