My understanding is that Zytiga restricts testosterone which feeds prostate cancer. Little, if any of the cancer, dies from that, but the PSA drops to sometimes "undetectable." If the biopsy results were correct, the cancer is still there and will *very likely* reassert itself as the effect of the Zytiga eventually -- as I understand almost always does -- wears off. (I have heard of -- but can't verify -- "hormone therapy," actually anti-hormone therapy like Zytiga, working for many years for SOME men.)