If you want some info on prostate cancer (PCa), here's an American Cancer Society page:
http://www.cancer.org/docroot/LRN/LRN_0.asp?dt=36
This topic should be on the radar of any man who's 45 or 50 years old and above.
My layperson's understanding is that this is a common cancer in men that often does not get detected early enough, unfortunately. However, as with many cancers, early detection is the key to effective treatment. If it goes untreated long enough, cancer cells can shed from the original tumor to other sites, making the problem more difficult to manage.
The PSA test is a simple blood test that measures the levels of prostate-specific antigen in the bloodstream. My previous 2 primary-care physicians did not believe in the test (for reasons your doctor can explain to you). My current physician does, and I'm glad of it, myself.
Certainly I hope the best for Tiger's dad.