Genetic detection of lymph node micrometastases in colorectal cancer

Objective: This study was undertaken to detect lymph node micrometastases in colorectal cancer patients by using reverse transcriptase polymerase chain reaction (RT PCR). Methods: A total of 205 lymph nodes, obtained from 17 colorectal cancer patients who underwent curative operation, were detected for expression of cytokeratin 20(CK20) mRNA with RT PCR. Thirty one lymph nodes from 4 patients with benign gastrointestinal disease were served as negative control. Cell spiking experiment was performanced to determine the sensitivity of this method. Results: Thirty five of 205 lymph nodes samples in colorectal cancer patients were shown CK20 mRNA expression, while only 18 samples were histologically positive. CK20 mRNA expression was undetected in 31 lymph nodes of benign disease. The result of cell spiking experiment indicated that the limit of sensitivity were 1 tumor cell per 105 normal lymphoytes. Conclusion: RT PCR for CK20 is a sensitive and specific method to detect lymph node micrometastases in colorectal cancer. It is superior to routine histopathological assay in examining lymph node metastases. Micrometastases detection by RT PCR may improve clinical staging and indications for cancer therapy.