Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Stage IV cancers have already spread to nearby areas such as the bladder or rectum (T4), to nearby lymph nodes, or to distant organs such as the bones. A small portion of T4 cancers may be curable using some of the same treatments for stage III cancers. Most stage IV cancers can’t be cured, but are treatable. The goals of treatment are to keep the cancer under control for as long as possible and to improve a man’s quality of life. In you case treatment seems working good. Zytiga is an anti androgen used in the treatment of prostate cancer because prostate cancer growth depends on androgen. Hope I have answered your query. Let me know if I can assist you further.