Possible anti-tumor activity of initial treatment with zoledronic acid with hormonal therapy for bone-metastatic prostate cancer in multicenter clinical trial

To ascertain the anti-tumor effect of zoledronic acid (ZOL) treatment on clinical outcomes in patients with bone metastatic prostate cancer, we examined the effect of ZOL started simultaneously with hormonal therapy as initial treatment in these patients. Forty-seven patients with bone-metastatic prostate cancer who received a luteinizing hormone releasing-hormone (LHRH) analogue and an anti-androgen [maximal androgen blockade (MAB)] were assigned to receive ZOL (4 mg intravenous administration every month for 2 years). The time to progression (TTP) of the prostate-specific antigen (PSA), the overall survival (OS), and the rate of PSA decrease in patients with MAB and ZOL treatment (ZOL group) were compared with these parameters in patients who received only MAB at one institute as a control group (non-ZOL group). Although the nadir PSA level and the rate of PSA normalization showed no significant differences between the ZOL and non-ZOL groups, the time to nadir PSA in the ZOL group was significantly shorter than that in the non-ZOL group (P < 0.05, Mann-Whitney U-test). There was a significant difference in TTP (P = 0.017, log-rank test) between the ZOL and non-ZOL groups, and statistically significant differences in TTP and OS between the ZOL and non-ZOL groups (P = 0.044 and 0.035, log-rank test) were recognized particularly in patients with advanced disease (extension of disease, grade 3 and 4). Simultaneous administration of ZOL and MAB as initial treatment delayed TTP in bone-metastatic prostate cancer patients. Initial treatment with ZOL has the possibility of anti-tumor activity to delay disease progression.