Changing levels of circulating tumor cells in monitoring chemotherapy response in patients with metastatic breast cancer.

BACKGROUND The detection of >5 circulating tumor cells (CTCs)/7.5 ml blood in patients being treated for metastatic breast cancer (MBC) has recently been shown to be predictive for therapy efficacy. The aim of this study was to investigate whether changing CTC levels during the course of chemotherapy treatment would also be useful in monitoring response to treatment. PATIENTS AND METHODS CTC levels were determined in 58 MBC patients at the beginning and after 3 cycles of chemotherapy. Changes in CTC level (either negative CTCs (<5 CTCs/7.5 ml blood) turning positive, vice versa, or a change of ±25%) were correlated to radiologic Response Evaluation Criteria In Solid Tumors (RECIST) criteria, as well as serum CA 15-3 measurements, and were evaluated for their capability to predict survival. RESULTS Changing CTC levels significantly correlated with response to therapy as measured by radiologic RECIST criteria (p<0.001), and serum CA 15-3 level changes (p=0.017). Patients with decreasing CTC levels survived significantly longer than patients with increasing CTC levels (17.67±5.90 months versus 4.53±0.54 months, p<0.001). CONCLUSION The observation of changes in CTC level during the course of chemotherapy is useful in monitoring therapy efficacy and is correlated with overall survival. Further prospective trials should investigate the clinical usefulness of determining changes in CTC level during chemotherapy of MBC.