Potential of circulating tumor cells as blood-based biomarkers in cancer liquid biopsy

Despite the first reports of circulating cells from solid tumors shed light on the circulation in deceased and in living patients in 1869 [1] and the mid 1950s [2], respectively, it took almost 50 years until the introduction of the CellSearch^® system by Veridex (now Janssen Diagnostics, LLC, Raritan, NJ, USA) as well as its approval by the US FDA [3] in 2004 paved the way for widespread clinical assessment of the number of circulating tumor cells (CTCs) as a prognostic diagnostic tool. The technology is based on enumeration of cells expressing the epithelial marker EpCAM and excludes cells positive for the hematopoietic cell surface marker CD45. The number of EpCAM⁺/CD45^– cells correlate with prognosis and are being used to monitor the response to chemotherapy in metastatic breast [4], prostate [5] and colorectal cancer [6]. This information can be used to spare cancer patients who are not responding to therapy the burden of adverse effects [7,8].

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