This method included: direct comparison of different samples of colon mucosa and blood cells, searching for epithelial-specific genes among the 20,000 genes assayed by microarray slides; identification of candidate marker mRNAs by data analysis, which allowed for only 10 putative differentially expressed genes; selection of some of the most suitable mRNAs (TMEM69, RANBP3 and PRSS22) that were assayed in blood samples from normal subjects and patients with colon cancer as possible markers for the presence of epithelial cells in the blood, using RT-PCR. This evidence concerns the gene PRSS22 and colonic neoplasm.