The existence of occult metastasis in peripheral blood has been reported in various tumors. However, in gastric cancer (GC), this metastasis has not been well analyzed. In the present study, to identify circulating cancer cells in patients with GC, peripheral blood samples from GC patients were investigated. Total RNA was extracted from 1.5 ml peripheral blood from 55 patients with GC, from 34 non-cancer patients, and from 10 healthy volunteers. Carcinoembryonic antigen (CEA), cytokeratin 19 (CK19), and 20 (CK20) messenger RNA (mRNA) were used as probes to detect GC cells in the blood samples using real-time reverse transcriptase polymerase chain reaction (RT-PCR). CEA and CK19 mRNA expression were not detected in the 40 healthy volunteers and non-cancer patients, while 2 of the 40 showed CK20 mRNA expression. In 55 patients with GC, CK19 mRNA was not detected and CEA mRNA was detected in only one case (1.8%) with stage IV. While CK20 mRNA expression was observed in 15 cases (27.3%) and even in stage I, 8 of 24 (33.3%) showed CK20 mRNA expression. Thus, the specificity of CK20 marker may be low. Even though the sensitivity of CEA marker is low, CEA may be a more reliable marker than cytokeratins for detection of cancer cells in GC patient's peripheral blood.

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