The selenium is a good choice, but I recommend upping it to 200mcg 3 times daily.
Suma is another excellent choice since it is the highest herbal source of germanium, which is highly antitumor.
Turmeric fights cancer through a number of different mechanisms. It is cheap, safe and readily available. You can add it to most foods.
Prostate cancer is actually caused from the human papilloma virus, so antiviral herbs are also highly recommended. Some of the best antivirals include chaparral, pau d' arco, and andrographis.