The article that reachout found, www.gyncancer.com/what-is.html
says that 30 doublings gives you the smallest tumor you can detect (0.25 inches in diameter, the size of a pea), and that 40 doublings gives you a lethal tumor. That gives you 10 doubling times to treat the cancer. It's hard to believe that you could detect a prostate cancer that small with a biopsy, so it may be more like 8 doublings.
The growth rate of most prostate cancer is dependent on hormones, so ADT must increase the doubling time. But HT reduces the PSA, so the cells must also actually die and go away, but HT fails if some cancer cells are not hormone dependent and keep on growing.