Receptor-binding cancer-associated surface antigen (RCAS1) and Estrogen receptor-binding fragment-associated gene 9 (EBAG9) proteins are identical. EBAG9/RCAS1 induces apoptosis and suppresses the growth of several cells such as activated T cells []. Defects in EBAG9 may be a cause of breast cancers and adenocarcinomas of the lung as it is present and overexpressed in many patients and the expression correlates with tumor grade, suggesting that it may be involved in cancer immune escape. It may not be a directly tumor-associated antigen, but rather contributes indirectly to the antigenicity of tumor cells. The selectivesuppression phenomenon of the cytotoxic immune response may be brought about by an increase in sRCAS1 blood serum concentration. Such an increase has been observed during cancer progression. RCAS1 blood serum concentration could be useful in the identification of endometriosis []and prostatic cancer [].
