766 detection of so-called epithelium-speciﬁc genes, which are potentially expressed in CTCs but not in blood nuclear cells. However, most analyzed tran- scripts exhibited variability in RT-PCR signals that hampered their recognition as speciﬁc markers for CTCs. This variability may be caused by many reasons. Although qRT-PCR greatly increases the sensitivity of mRNA detection, its usefulness as a speciﬁc method for CTC detection, speciﬁcally in blood specimens, is questionable. A low PCR signal signiﬁcantly decreases the reproducibility of inter- and intra-measurement results. In addition, PCR-based methods may detect both malignant and non-malig- nant epithelial cells circulating in the blood. Both cell types may be released into the blood due to undeﬁned reasons and with undeﬁned intervals [3], leading to their inconsistent presence in the circulation. For these reasons, the existing PCR-based methods of detecting CTCs have limited usefulness for clinical use. 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