The average survival of a patient with stage 4 prostate cancer is 1-3 years.
When bone metastases are present, they generally indicates a poor prognosis, and every treatment is just palliative (controlling symptoms).
Metastatic prostate cancer is usually controlled with hormone therapy for a period of time, often several years, but, eventually, most prostate cancers are able to grow despite hormone therapy.
Bone metastases can decrease the life expectancy to 6-9 months.