Circulating Tumor Cells in Prostate Cancer: From Discovery to Clinical Utility.

BACKGROUND: Prostate cancer represents the most common non-skin cancer type in men. Unmet needs include understanding prognosis to determine when intervention is needed and what type, prediction to guide the choice of a systemic therapy, and response indicators to determine whether a treatment is working. Over the past decade, the "liquid biopsy," characterized by the analysis of tumor cells and tumor cell products such as cell-free nucleic acids (DNA, microRNA) or extracellular vesicles circulating in the blood of cancer patients, has received considerable attention. CONTENT: Among those biomarkers, circulating tumor cells (CTCs) have been most intensively analyzed in prostate cancer. Here we discuss recent studies on the enumeration and characterization of CTCs in peripheral blood and how this information can be used to develop biomarkers for each of these clinical contexts. We focus on clinical applications in men with metastatic castration-resistant prostate cancer, in whom CTCs are more often detected and at higher numbers, and clinical validation for different contexts of use is most mature. SUMMARY: The overall goal of CTC-based liquid biopsy testing is to better inform medical decision-making so that patient outcomes are improved.