Circulating tumor cells in breast cancer.

Circulating tumor cell (CTC) measurement in peripheral blood of patients with breast cancer offers prognostic information. In this review, we will try to identify evidence that could be used for prognosis, predictive power to draw this tool to clinical utility. We reviewed 81 manuscripts, and categorized those in discovery datasets, prognostic factors in metastatic breast cancer, identification of clinical utility in early breast cancer and in novel approaches. With each patient responding differently to chemotherapy, more efficient markers would improve clinical outcome. Current CTC diagnostic techniques use epithelial markers predominantly; however, the most appropriate method is the measurement of circulating DNA. It has been hypothesized that micrometastasis occurs early in the development of tumors. That implies the presence of CTCs in nonmetastatic setting. The origin of stimulus for malignant transformation is yet unknown. The role of microenvironment as a stimulus is also being investigated. It has been shown that CTCs vary in numbers with chemotherapy. The markers, which are followed-up in the primary tumors, are also being studied on the CTCs. There is discordance of the human epidermal growth factor receptor-2 status between the primary tumor and CTCs. This review summarizes our current knowledge about the CTCs. With genetic profiling and molecular characterization of CTCs, it is possible to overcome the diagnostic difficulties. Evidence for clinical utility of CTC as prognostic and predictive marker is increasing. Appropriate patient stratification according to CTC determination among other tests, would make personalized cancer therapy more feasible.