Detection of circulating cancer cells by nested reverse transcription-polymerase chain reaction of cytokeratin-19 (K19) - Possible clinical significance in advanced gastric cancer

Intermediate filament cytokeratin-19 (K19) protein is expressed in normal and malignant gastrointestinal epithelial cells, but not in peripheral blood (PB). Small amount of circulating gastric cancer cells can be detected by a sensitive nested reverse transcription-polymerase chain reaction (RT-PCR) with primers specific for K19 mRNA. Thirty-four PB samples obtained from patients with inoperable/metastatic gastric cancer were examined. The mononuclear cell (MNC) fraction was collected by Ficoll centrifugation, and followed by total RNA extraction by acid guanidinium thiocyanate-phenol-chloroform method. RNA from 8 gastric cancer cell lines and the monocuclear cells of 33 healthy adults were used as positive and negative controls, respectively. DNA fragment of 774 bp amplified by the internal primers was found to be a highly reliable marker for K19 mRNA expression. The sensitivity of detection was between 1 and 10 cells/106 normal MNCs. The K19 transcripts were detected in 20.6% (7/34; 8-37%, 95% C.l) of PB samples. None of the other pertinent clinicopathological features, including the disease extent and the histopathologic types of the tumors, were related to the expression of K19 in PB. All 34 patients had been treated by systemic chemotherapy. Among the 17 non-responders to chemotherapy, the survival of the 4 patients with detectable K19 was significantly shorter than that of 13 patients without detectable K19 in their circulating blood (p = 0.014). However, the survival impact of K19 was less significant in the other 17 patients whose tumors had responded to systemic chemotherapy. Of the whole group of patients, the median survival of the 7 and 27 patients with and without detectable K19 in their circulating blood was 1 and 3.5 months, respectively (p = 0.368). We concluded that detecting circulating cancer cells by K19 nested RT-PCR is associated with poor prognosis of gastric cancer, particularly in those patients who are not responsive to systemic chemotherapy.