Hi Chuck,
I believe there have been variable response rates to Zytiga with prednisone as well as Zytiga with prednisone and Lupron. There are some here that have been on it for more than 4 years with excellent results. I have been on Zytiga for 26 months and have my labs checked every six weeks. There is a small blogspot that discusses its efficacy. I have pasted the link below
abiraterone.blogspot.com/2012/10/how-long-does-zytiga-work.html