It is known that Zoledronic acid (ZA) reduces the risk of developing skeletal-related events (SRE) which are caused by bone metastasis in prostate cancer (PCa). ZA also improves the quality of life (QOL).

ZA has become a standard supportive therapy for men with prostate cancer who have bone metastasis. The big unknown is when should a man start ZA treatment. In a recent study researchers investigated whether the combination of ZA and combined androgen blockade (CAB) could delay a PSA relapse of prostate cancer as well as prevent the development of SREs.

To look at this issue the researchers randomly sorted ithe subject men into two groups (combined androgen blockade (CAB) alone group and CAB + ZA treatment group).

In the CAB + ZA group, 4 mg ZA was intravenously administered every 4 weeks with the start of treatment. The first end point was a period to PSA relapse, and the secondary end point was SREs rate.

Untreated 60 men with prostate cancer  with bone metastasis were enrolled between 2006 and 2011.

Thirty one men were treated with CAB alone and 29 men were treated with CAB + ZA. There were no significant differences in the baseline characteristics in the both groups, and the mean observation period was 27.4 months and 32.1 months, respectively.

There was no significant difference in progression free survival (PFS) (p=0.073), tendency that CAB + ZA shows better PFS than CAB alone group was observed (time to 50% PFS was extended 11.6 months than CAB alone group). A sub-analysis using the men with a higher Gleason score over 7, CAB +ZA group showed significantly longer PFS than the CAB group (p=0.021). A significant difference was recognized in SRE rate between the two groups (p=0.019), ZA tended to delay the occurrence of SRE in men with prostate cancer.

This result indicates that the use of ZA at the beginning of hormonal therapy not only has a preventive effect on the occurrence of SREs but also a relapse-delaying effect, especially in men with high Gleason score and severe bone metastasis.

Through careful observation is essential, since the long-term use of ZA may increase the incidence of adverse effects, CAB-ZA treatment may be recommended for the treatment of PCa patients with bone metastasis.

J Clin Oncol 32, 2014 (suppl 4; abstr 207); Satoru Ueno, Atsushi Mizokami, Takashi Fukagai, Naohiro Fujimoto, Hitoshi Ohoka, Yukihiro Kondo, Gaku Arai, Hisamitsu Ide, Mikio Namiki.