The Medical Minute: Prostate cancer screening -- What's the use?

By John Messmer
Penn State Family and Community Medicine
Penn State Milton S. Hershey Medical Center
Penn State College of Medicine

It's the most frequently diagnosed cancer in men and the third leading cause of cancer death among men after lung and colon cancer. So, one might think it makes sense to screen for it. Screening tests are well established for other cancers: colonoscopy for colon cancer, mammography for breast cancer, Pap smears for cervical cancer. Why not for prostate cancer?

When a test is done because of a symptom or physical finding, it is a diagnostic test, not a screening test. Screening is a way of finding a problem when no symptoms or other abnormalities exist. A screening test for cancer should be fairly sensitive, that is, it should find cancer when present. It should be fairly specific, that is, a positive test is because of cancer, not some other problem.

Screening tests may be appropriate only for certain groups based on gender or age. It makes no sense to screen women for a disease only men get. Similarly, if detecting and treating the problem will add only 10 years of life, it may be inappropriate for people with a life expectancy of less than 10 years. If the disease diagnosed by screening is mild and the treatment results in a high rate of unpleasant side effects, perhaps screening should be avoided.

More men over age 50 are screened for prostate cancer than for colon cancer according to a 2003 article in the Journal of the American Medical Association. That's interesting, because colon cancer screening is more likely to save lives than prostate cancer screening, but screening for prostate cancer is easier to do.

Proponents of prostate cancer screening might point out there is an increase in the diagnosis of prostate cancers due to screening and increased survival with early diagnosis. But the counter argument is that this represents biases based on lead time and length. That is, more screening will find tumors earlier, but will include many non-aggressive tumors that would not have caused any problems because of slow growth or the men would have died of some other problem before the prostate cancer affected them.

If early diagnosis results in cure, should we really care whether or not the cancer would have lead to death? Isn't it better just to have the cancer out? Maybe not, since this is one problem for which the treatment in some cases might be worse than the disease. Some of the treatment medications can increase the risk of heart disease, a more common disease in men than prostate cancer. Impotence and urine leakage can complicate surgical treatment and radiation can cause bladder or rectal pain. If screening is supposed to help, treatment should result in increased quality of life.

Prostate cancer screening usually means a blood test for prostate specific antigen (PSA) and might include a digital rectal examination (DRE) of the prostate. PSA is a chemical made only by the prostate which serves to liquefy the semen after ejaculation. A small amount is found in the blood normally, but elevated levels are found in prostate cancer in addition to many benign prostate conditions, most commonly benign prostatic hypertrophy or enlargement that comes with age. DRE can find larger tumors, but tends to miss tiny ones. However, it is useful when the PSA is only slightly elevated. If DRE shows the prostate to be very large, the PSA may be high because of the increased size of the prostate.

Unfortunately, low levels of PSA do not guarantee the absence of prostate cancer and high levels do not mean cancer is definitely present. Some PSA is bound to blood proteins and some is not. The latter is called "free" or "unbound" PSA. Lower levels of "free" PSA may be more indicative of cancer, but there is currently insufficient data to say that with certainty.

Since the scientific data is not able to show that prostate screening is always beneficial, recommendations on screening are different from different groups. The U.S. Public Health Service Task Force makes no recommendation on DRE and says there is insufficient evidence to recommend PSA testing. The American Cancer Society and American Urologic Association recommend DRE annually for men over 40 and PSA annually for men over 50 after being informed of the risks vs. the benefits. The Canadian Task Force on Prevention Health Care said there is poor evidence to do DRE at all and it recommends against doing PSA on anyone.

So, what's a guy to do? No single answer is applicable to all men. Higher risk individuals include African-American and Hispanics, obese men and men with a family history of prostate cancer under age 60, so those men might benefit more from screening starting at age 40 or so. Other men can be informed of the risks and benefits of screening and make individual decisions. Since prostate cancer in men under age 70 tends to be more aggressive, PSA may be useful in this age group as long as their life expectancy is more than 10 years. After age 70 it is even less clear, since prostate cancer is less likely to be a cause of death. Otherwise healthy men with longer life expectancies may be helped by screening, but the anxiety of having to deal with a borderline PSA may create unnecessary unhappiness.

It's a good idea to have a personal physician to help with the decision to screen or not. Everyone's circumstances are different so having someone to help sort the ifs, ands, and buts can make it easier. For men without a personal physician, many hospitals participate in prostate cancer screenings during September which is prostate cancer awareness month. Regardless where screening is performed, men must ask what the results mean to them as individuals and whether it is even appropriate to screen them at all.