A more reliable tumor marker is needed as a prognostic indicator in metastatic castration-resistant prostate cancer. Circulating tumor cells (CTCs) are cells that have broken away from a tumor and flow in the bloodstream. Evidence has indicated that the presence of CTCs in the peripheral blood of men with solid malignancies correlates with clinical outcomes. When the CTC number is reduced to fewer than five cells per 7.5 ml of blood, survival outcomes often improve. The relationship between the number of CTCs and prognosis has the potential to influence treatment decisions. Therefore, oncology nurses and practitioners must evaluate the scientific evidence, understand the clinical implications, and realize the impact CTC counts may have on practice to effectively communicate the CTC results to a patient. In addition, oncology nurses and practitioners must know that although favorable changes in CTC count are associated with a better prognosis, that alone cannot be used to guide treatment decisions for an individual.