Cancer testis (CT) antigens are attractive targets for cancer immunotherapy 
because their expression is restricted in normal germ line tissues but 
frequently detected in variety of tumors. OY-TES-1 is identified as a member of 
CT antigens. Current knowledge about OY-TES-1 expression in colorectal cancer 
(CRC) is solely based on mRNA analysis. None of previous researches has studied 
OY-TES-1 at protein level. In this study, OY-TES-1 polyclonal antibody was 
generated. The expression of OY-TES-1 mRNA and protein was detected by RT-PCR 
and immunohistochemistry in 60 CRC and paired adjacent non-tumor tissues, 24 
colorectal adenoma and 3 normal colon tissues, respectively. Sera from 73 CRC 
patients were also tested for OY-TES-1 antibody by ELISA. Our results showed 
that the frequency of OY-TES-1 mRNA expression was statistically higher in CRC 
(73.3%, 44/60) than that in adjacent non-tumor tissue (55.0%, 33/60) and 
colorectal adenoma (45.8%, 11/24). For the first time, OY-TES-1 protein 
expression was found in (43.3%, 26/60) of CRC tissues, but absent in any of 
adjacent non-tumor and colorectal adenoma tissues. No OY-TES-1 expression was 
found in normal colon by either RT-PCR or immunohistochemistry. Furthermore, 
OY-TES-1 protein expression was correlated with tumor invasion stage (P=0.004) 
and histological grade (P=0.040). Anti-OY-TES-1 antibody was detected in (9.6%, 
7/73) of CRC patients' sera but not in 76 healthy donors. This finding 
demonstrates that OY-TES-1 is frequently expressed in CRC and is able to induce 
humoral immune response spontaneously in CRC patients, suggesting that it might 
be a promising immunotherapy target for CRC.