Quest for the Ideal Cancer Biomarker: An Update on Progress in Capture and Characterization of Circulating Tumor Cells

Preclinical Research The quest for a well-validated, non-invasive biomarker to aid in clinical decision making has remained elusive in the cancer space over the last 30 years. Much promise has been attached to circulating tumor cells (CTCs) as prognostic, predictive, and pharmacodynamic biomarkers with the potential to eliminate the need for invasive tumor biopsies and improve on the clinical value of other circulating tumor markers. The CellSearch® system (Veridex, LLC., Raritan, NJ, USA) cleared the U.S. Food and Drug Administration when the presence of CTCs was shown to have prognostic significance in patients with breast, prostate, and colorectal cancer. However, CTCs are not, at present, routinely being used in the clinic to guide treatment decisions. This paper discusses key attributes that a biomarker must possess, the status of other potential cancer biomarkers, and advancements in the capture and characterization of CTCs that will enable actualization of their potential as a reliable and efficient biomarker of disease diagnosis, progression, and response to therapy in the clinic.