Many prostate cancer clinical trials are often in progress. Most of these are small clinical trials with only a small number of people being treated. If a small clinical trial shows that a treatment may work well, a larger clinical trial is then done. The treatment may then be tested on hundreds or even thousands of men. Other types of clinical trials for prostate cancer look for new ways to help prevent it, better ways to find it early, and ways to tell if it will grow quickly or not.