Circulating tumor cells in solid cancer: tumor marker of clinical relevance?

Circulating tumor cells (CTC) can be detected in the peripheral blood of patients with a variety of solid cancers. Because of their very low frequency, these tumor cells are not easily detected using conventional cytology methods. In the past decade, numerous groups have attempted to detect CTC of solid malignancies using the highly sensitive reverse transcriptase polymerase chain reaction, which has been shown to be superior to conventional techniques. However, the biological significance of CTC and the therapeutic relevance of their detection are still debated. This article reviews the most recent findings on this subject, and discusses the potential of identification and molecular characterization of the subset of CTC responsible for metastasis development. Confirming the prognostic value of CTC would provide clinicians with a unique tool for better stratification of patients' risk and provide basic researchers with a new target for the development of novel therapeutic approaches.