Abstract: A cancer test having prognostic utility in predicting time to disease progression, overall survival, and response to therapy in patients with MBC based upon the presence and number of CTC's. The Cell Spotter® System is used to enumerate CTC's in blood. The system immunomagnetically concentrates epithelial cells, fluorescently labels the cells and identifies and quantifies CTC's. The absolute number of CTC's detected in the peripheral blood tumor load is, in part, a factor in prediction of survival, time to progression, and response to therapy. The mean time to survival of patients depended upon a threshold number of 5 CTC's per 7.5 ml of blood. Detection of CTC's in metastatic cancer represents a novel prognostic factor in patients with metastatic cancers, suggests a biological role for the presence of tumor cells in the blood, and indicates that the detection of CTC's could be considered an appropriate surrogate marker for prospective therapeutic clinical trials.