Detecting circulating cancer cells using reverse transcriptase-polymerase chain reaction for cytokeratin mRNA in peripheral blood from patients with gastric cancer

Background: Cytokeratins (CKs) 19 and 20 have been used as targets for detecting cancer cells. We attempted to detect circulating cancer cells in patients with gastric cancer using a high-sensitivity reverse transcriptase-polymerase chain reaction (RT-PCR) assay for CK transcripts. Methods: PT-PCR for CK 19 and CK 20 was performed on peripheral blood samples obtained from 52 patients with gastric cancer, from 24 of whom blood samples were collected on three occasions. Fourteen healthy volunteers served as controls. Results: CK 19 and CK 20 were positive in five (9.6%) of 52 patients with gastric cancer. Of these five, four were classified into stage IV and the other stage I, according to the TNM Classification. In gastric cancer patients, three (12.5%) were positive in the 24 cases examined three times and two (7.1%) were positive in 28 cases examined only once. Among the stage IV cancer, positive cases for CK showed significantly lower survival rates than those negative for CK. Between CK 19 and CK 20 in the 24 cases examined three times, CK 19 was found to be more sensitive in detecting cancer cells. CK 20 was detected in one (7.0%) of 14 healthy volunteers, whereas CK 19 was not detected. Conclusions: We conclude that repeated blood sampling may be desirable to detect circulating cancer cells in peripheral blood, even in patients with advanced gastric cancer; CK 19 may be superior to CK 20 in detecting these cells. The clinical significance of detecting occult cancer in peripheral blood remains to be determined.