Detection and clinical application of circulating cancer cells, using highy pricise cancer cell determination system

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Real time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) was used to detect disseminated cancer cells in bone marrow and peripheral blood. First of all, we compared CEA, CK18 and CK20 expression using 4 gastric cancer cell lines and 3 normal tissue cell lines in order to select the most appropriate marker for detection of disseminated gastric cancer cell in bone marrow. CK20 proved to be the most promising marker since the expression level of normal cell lines was extremely low and about 50- to 100-fold differences were found between gastric carcinoma cell lines and normal tissue cell lines. We also screened bone-marrow RNA of 47 patients with gastric cancers, using this system. Among the three markers we tested, with only about CK20 could we find that 27 of 47 patients were positive.Next, we studied the detection of circulating tumor cells in peripheral blood in patients with gastric cancer using Quantitative RT-PCR. Common mRNA targets for RT-PCR for detection of small numbers of cancer cells in gastric cancer are CK18,CK19,CK20, and CEA. The number of CK19 and CK20 mRNA copies was significantly increased in patients with a non-curative operation or recurrence of gastric cancer (CK19;p=0.0087, CK20;p=0.0022) compared with healthy volunteers. There was a significant difference in tumor stages between CK19 positive and negative patients with curative disease on preoperative diagnosis. Five-year survival rates of patients with CK19 positive or negative cases were 50.0% or 79.0%, respectively (p=0.0347). In conclusion, micrometastases of gastric cancer can be detected in circulating peripheral blood using quantitative real-time RT-PCR. CK19 is a better marker than CK18,CK20 and CEA for peripheral blood, and could be clinically useful to estimate prognosis or to make a postoperative strategy of adjuvant treatment.