Circulating tumor cell count during zoledronic acid treatment in men with metastatic prostate cancer: a pilot study

PURPOSE: Recent clinical trials have demonstrated that zoledronic acid (ZOL) significantly prolongs survival in prostate cancer patients undergoing androgen deprivation therapy. This pilot study investigated the influence of ZOL on circulating tumor cell (CTC) counts in prostate cancer patients in association with prostate-specific antigen (PSA) used as a serum biomarker. METHODS: Patients with metastatic castration-resistant prostate cancer (CRPC) who were CTC-positive (n=4) were enrolled in treatment with ZOL between April 2012 and December 2013. CTCs were detected using the Cell Search System. The study evaluated CTC fluctuations at 1, 2, and 3 months versus baseline, as well as patient outcomes and adverse events. RESULTS: Two patients showed evidence of temporally decreased CTCs after ZOL treatment. Instead of decreasing the number of CTCs, the PSA level did not go down during the ZOL treatment. One patient could not undergo ZOL treatment due to rapid disease progression. CONCLUSIONS: Although CTC count arguably provides useful information about patients undergoing ZOL treatment, the positive influence of ZOL may be limited to temporary effects for CRPC.