Systematic identification and validation of candidate genes for detection of circulating tumor cells in peripheral blood specimens of colorectal cancer patients.

The presence of tumor cells in peripheral blood is being regarded increasingly as a clinically relevant prognostic factor for colorectal cancer patients. Current molecular methods are very sensitive but due to low specificity their diagnostic value is limited. This study was undertaken in order to systematically identify and validate new colorectal cancer (CRC) marker genes for improved detection of minimal residual disease in peripheral blood mononuclear cells of colorectal cancer patients. Marker genes with upregulated gene expression in colorectal cancer tissue and cell lines were identified using microarray experiments and publicly available gene expression data. A systematic iterative approach was used to reduce a set of 346 candidate genes, reportedly associated with CRC to a selection of candidate genes that were then further validated by relative quantitative real-time RT-PCR. Analytical sensitivity of RT-PCR assays was determined by spiking experiments with CRC cells. Diagnostic sensitivity as well as specificity was tested on a control group consisting of 18 CRC patients compared to 12 individuals without malignant disease. From a total of 346-screened genes only serine (or cysteine) proteinase inhibitor, clade B (ovalbumin), member 5 (SERPINB5) showed significantly elevated transcript levels in peripheral venous blood specimens of tumor patients when compared to the nonmalignant control group. These results were confirmed by analysis of an enlarged collective consisting of 63 CRC patients and 36 control individuals without malignant disease. In conclusion SERPINB5 seems to be a promising marker for detection of circulating tumor cells in peripheral blood of colorectal cancer patients.