The phase III trials for both Xtandi and Zytiga were similar. Both trials investigated men who progressed or died against placebo. Only 14% of men taking Xtandi during the trial progressed or died compared to 40% of the men in the placebo group. In the phase III trial of Zytiga 28% of the men progressed or died, compared with 46% on placebo. It appears that almost twice as many men died or progressed in the Zytiga group opposed to the Xtandi group.
These two trials were not head-to-head clinical trials, so any comparisons must be taken with a grain of salt.
Xtandi, unlike Zytiga it does not require the concurrent taking of Prednisone, a steroid that has side effects.
If your doctor suggests that you take Zytiga and prednisone instead of Xtandi ask, why.