In addition to the prognostic value of CTC detection, it can also be used as a tool to measure systemic treatment response – Xenidis, et al. demonstrated that cytokeratin-19 (CK-19) mRNA-positive circulating tumor cells (CTCs) detection in the peripheral blood of women with early-stage breast cancer following chemotherapy was a significant predictor of treatment success, with patients in which CTCs remained after chemotherapy having more frequent clinical relapses and a poorer overall survival [4]. Here, KRT19 is linked to breast cancer.