Previously, we established a qualitative nested endpoint RT-PCR specific for cytokeratin (CK)20-mRNA, coding for an intermediate filament protein of epithelial cells, which has been shown to detect CTC within a fraction of peripheral blood mononuclear cells (PBMC) with a high specificity and sensitivity in the blood of CRC patients [12, 13]. The gene discussed is KRT20; the disease is colorectal carcinoma.