Circulating tumor cells in prostate cancer: beyond enumeration.

Circulating tumor cells (CTCs) are a population of rare cancer cells that have detached from the primary tumor and/or metastatic lesions and entered the peripheral circulation. Enumeration of CTCs has demonstrated value as a prognostic biomarker, and newer studies have pointed to information beyond enumeration that is of critical importance in prostate cancer. Technologic advances that permit examination of the morphology, function, and molecular content of CTCs have made it possible to measure these factors as part of liquid biopsy. These advances provide a way to study tumor evolution and the development of resistance to therapy. Recent breakthroughs have created new applications for CTCs that will affect the care of patients with prostate cancer.