Molecular signature detection of circulating tumor cells using a panel of selected genes

Circulating tumor cell (CTC) detection in peripheral blood of colon and other epithelial cancer patients is becoming a scientifically recognised indicator for the presence of primary tumors and/or metastasis. The resulting need to further develop CTC detection-based systems for improved diagnosis, prognosis and assessment of therapy efficacy in tumour patients has prompted the application of different approaches, including expression analysis of tissue-specific and epithelial genes. In this context, lack of specificity of the analysed genes remains a fundamental problem for reliable CTC detection. In this study, we have selected a panel of highly specific epithelial genes: cytokeratin 20 (CK20), cytokeratin 19 (CK19), carcinoembryonic antigen (CEA) and guanylyl cyclase C (GCC), and performed RT-PCR analysis to assess their expression in total blood and in different cell fractions of peripheral blood (PBMC and CD45-negative population) of cancer patients and healthy controls. Our results demonstrate that analysis of a single gene in a CTC-enriched population (CD45(-) peripheral blood cells) of cancer patients allows detection of a CTC molecular signature in at most 63.3% of cases, while analysis of all four genes performed in all three sample types increases the detection of positive patient samples to 87.7%. Healthy controls did not show positivity for any combination of these genes, although positivity was observed for the CEA marker alone, which was detected in 3 (6.6%) out of 45 donors, and only in the CD45(-) fraction. Here, we demonstrate that combined analysis of the genes above, in multiple blood fractions, results in a highly specific and sensitive CTC detection system in patients with metastatic solid tumors. Therefore, we believe that validation on a large scale of this approach, which demonstrates higher specificity in patients compared to controls, could become a relevant CTC screening test in patients with established metastatic disease, and furthermore, may also be useful for evaluating the possible presence of CTCs before the onset of clinically manifested metastatic spreading.