Your prostate makes prostate-specific antigen (PSA), as do most prostate cancer cells. During prostate cancer treatment, changes in your PSA levels help show whether your treatment is working.
When you get treatment -- whether it's chemotherapy, hormone therapy, a vaccine, or a combination -- your PSA levels should drop and stay low. If you have surgery to remove your prostate, you shouldn't have any PSA levels that can be found in a test.