Circulating tumor cells as biomarkers in cancer

Circulating tumor cells (CTCs) can be found in the peripheral blood of metastatic cancer patients. Recently, with the development of technologies sufficiently sensitive to detect very rare cells, there has been a considerable increase in research to improve detection of CTCs. Here we discuss the current technologies employed for the enumeration and characterization of CTCs. The implementation of such technologies has enabled research into determining the clinical significance of CTCs and has shown that the concentration of CTCs in patient blood correlates with prognosis and is a clinically relevant prognostic biomarker for patients with metastatic breast, prostate, and colorectal cancers. Additionally, CTCs may be a useful marker for more accurately staging patients as well as to identify early-stage patients at risk of developing metastatic disease who are likely to benefit from a more aggressive adjuvant therapy. Furthermore, various studies have shown that temporal monitoring of CTCs can be used to evaluate patient responses to therapy and to detect genetic and phenotypic changes to tumors in real time, allowing more effective treatment guidance