Circulation of cancer cells in the blood is a mandatory step for metastasis, but circulating tumor cells (CTC) have a low metastatic efficiency in preclinical animal models. In this prospective study, we reported the clinical outcome of nonmetastatic breast cancer patients according to CTC detection.

In 115 nonmetastatic patients diagnosed with large operable or locally advanced breast cancer, we prospectively detected CTC using the CellSearch system before and after neoadjuvant chemotherapy in a phase II trial (REMAGUS02).

At baseline, 23% of patients were CTC positive, but only 10% had >1 CTC/7.5 ml of blood. After a median follow-up of 36 months, CTC detection before chemotherapy was an independent prognostic factor for both distant metastasis-free survival [DMFS; P = 0.01, relative risk (RR) = 5.0, 95% confidence interval (CI) 1.4–17] and overall survival (OS; P = 0.007, RR = 9, 95% CI 1.8–45). CTC detection after chemotherapy was of less significance (P = 0.07 and 0.09, respectively). Moreover, CTC detection showed interesting characteristics as an individual predictive test for metastatic relapses (sensibility 55%, specificity 81%, and global accuracy 77%).

Detection of ≥1 CTC/7.5 ml before neoadjuvant chemotherapy can accurately predict OS. Our findings may change the clinical management of nonmetastatic breast cancer and indicate that the metastatic efficiency of CTC could be higher than previously reported.