PSA (Prostate-Specific Antigen) is a simple blood test that serves as an important marker of prostate cancer. It's discovery has been the major reason that prostate cancer is caught at much earlier stages than in previous years. In fact, it's also the major reason that patients with newly diagnosed prostate cancer typically have no symptoms (other than an elevated PSA).
Prior to the discovery of PSA, prostate cancer was detected only at more advance stages - when the patient had symptoms or the cancer could be felt on digital rectal examination (DRE). The mortality (death) rates from prostate cancer in the current decade is lower than that in the last decade largely because of the increased use and awareness of PSA.
But like any screening test, PSA is not perfect. It can be falsely elevated due to 1) benign enlargement of the gland, 2) infection, 3) inflammation such as prostatitis, and 4) recent sexual activity. Elevation of PSA, when due to cancer, does not distinguish slowly growing cancers from aggressive ones.
Should I get the PSA test?
There is no "one-size-fits-all" answer to this question. There is clearly a major debate right now on PSA. PSA can pick up cancers at such early stages, that in many situations, such cancers may not be life-threatening. For this reason, some groups such as the USPSTF recommend against routine screening. It's also argued that men who are detected with cancer will overwhelmingly choose treatment, rather than consider more conservative treatment options.
However, my opinion is that PSA screening is valuable, when used appropriately, and in conjunction with new biomarkers and clinical tools. Firstly, PSA gives the patient and physician more information and does not commit a patient to any further evaluation or treatment. Secondly, many men benefit from the PSA - the large European randomized study and studies of prostate cancer in Sweden have shown early detection to save lives. Finally, I don't believe the argument that patients are automatically going to elect treatment. In today's computer-savvy world, patients have the tools to research all treatment options (including active surveillance) and decide what treatment is right for them.