Detection of circulating gastric cancer cells in peripheral blood using real time quantitative RT-PCR.

Background/aims: Detection of occult cancer cells in peripheral blood or bone marrow has recently received a great deal of attention regarding the prediction of postoperative recurrence of the cancer, and for novel strategies of adjuvant therapy. This study addresses the detection of circulating tumor cells in peripheral blood in patients with gastric cancer using Quantitative RT-PCR.

Methodology: Common mRNA targets for RT-PCR for detection of small numbers of cancer cells in gastric cancer are CK18, CK19, CK20, and CEA. Ten milliliter of peripheral venous blood was taken from 14 healthy Japanese volunteers and 101 patients with gastric cancer. Samples were analyzed using real-time TaqMan technology and a Model 7700-sequence system. The group of gastric cancer patients included 69 individuals with curative disease on preoperative diagnosis and 32 individuals with a non-curative operation or recurrence of the disease.

Results: 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. Cut-off levels of CK19 or CK20 copy numbers were determined by the maximum value of healthy volunteers. For CK19, there were 61 (88.4%) negative cases and 8 (11.6%) positive cases in 69 individuals with curative gastric cancer. There was a significant difference in tumor stages between CK19 positive and negative patients with curative disease on preoperative diagnosis. For CK20, there were 59 (85.5%) negative cases and 10 (15.5%) positive cases. There was no statistical difference between CK20 positive and negative cases for all clinicopathological factors. On postoperative day 14, there was a significant difference between positive and negative cases regarding tumor size, tumor stage, and lymph node metastasis for CK19, and tumor stage and lymph node metastasis for CK20. Five-year survival rates of patients with CK19 positive or negative cases were 50.0% or 79.0%, respectively (p=0.0347). While, for CK20, 5-year survival rates for positive cases was 51.9%, and for negative cases 78.9% (p=0.0490).

Conclusions: 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, and could be clinically useful to estimate prognosis or to make a postoperative strategy of adjuvant treatment.