Editor's note: CNN conditions expert Dr. Otis Webb Brawley is the chief medical officer of the American Cancer Society, a world-renowned cancer expert and a practicing oncologist.
(CNN) -- Q: The New England Journal of Medicine has published more information on prostate cancer screening. Why is it so controversial?
A: Approximately 28,200 American men will die of prostate cancer in 2012. Among cancers, only lung cancer kills more men in the U.S. each year.
This week's issue of the New England Journal of Medicine has a follow-up evaluation of The European Randomized Study of Screening for Prostate Cancer (ERSPC), which analyzed data from 162,000 men.
The ERSPC study concluded that screening reduced an individual's relative risk of prostate cancer death by 21%.
Many will quickly interpret this to mean that prostate screening with the blood test known as PSA saves lives. But the paper deserves a deeper examination, as the findings are not that simple.
Prostate cancer screening has been common in the U.S. since the early 1990s. Mass prostate screening, where large numbers of men are encouraged to get the test at health fairs, shopping malls and community meetings has become a lucrative part of the business plan for many hospitals, clinics and medical practices. So it's surprising to note that the 2009 ERSPC publication was the first well-designed clinical trial to even suggest that screening saves lives.
The ERSPC reported a 21% decrease in relative risk of death in 2009. Put into perspective, a 21% decline in relative risk means that a man choosing screening goes from a lifetime risk of prostate cancer death of 3% to a lifetime risk of 2.4%. Here they found that 1,055 men would need to be screened to identify 37 men with prostate cancer and save one life.
To be fair, not all accepted cancer screening tests have demonstrated a decrease in overall mortality.
Trials have shown breast cancer mammography has met this standard, as has lung cancer screening using low dose spiral CT.
I am aware of no cervical cancer or colorectal cancer screening studies showing a decrease in overall mortality, but many have shown a decrease in the incidence of disease. Reducing the number of people getting the cancer is another accepted benefit of screening.
Q: Why do we need a new study of prostate cancer screenings?
A: The purpose of a screening test is to save lives. A test is not necessarily successful in saving lives if it simply finds cancer. I believe it is not necessarily a successful test it finds disease earlier and leads to an increase in the number of people surviving five or 10 years after diagnosis.
Screening is only successful if it decreases the number of people dying from the disease. Unfortunately this important point about screening is not widely understood beyond those with expertise in screening. Indeed, a recent study in the Annals of Internal Medicine suggests that this point is not appreciated by more the 75% of practicing physicians.
The only way to truly determine if screening saves lives is through taking a large number of people at risk for the disease and randomly assigning half to get the experimental test on a regular basis over time and half to not get the test over the same period of time.
The two groups are then watched to see if the number of deaths from the cancer and the all-causes mortality rate differs in the two groups.
The double edge sword of cancer screening is that screening itself can cause harm.
Prostate cancer screening can detect and diagnosis a cancer that would never have needed treatment. The subsequent unnecessary treatment can cause incontinence, sexual impotence and even death.
Indeed studies show that about 1% of men undergoing prostate cancer surgery in the U.S. die due to the surgery. The European study investigators estimate that half of all the cancers they diagnosed fell into the category of those not needing treatment. Most men elected to have treatment.
Q: So should I get screened, or not?
A: In draft guidelines issued in the fall of 2012, the U.S. Preventive Services Task Force noted that four studies published over the past 15 years have documented the harms of prostate cancer screening and only the ERSPC has suggested that screening leads to a mortality reduction.
They use this as reasoning to recommend against prostate cancer screening.
When one takes a hard look at the scientific data, the benefits of screening are not at all clear. Given the uncertainty, I believe:
-- Mass screenings should stop.
-- Screening should only be done within the physician-patient relationship.
Doctors and the men they serve need to learn the true facts about screening. Only after understanding the known harms and potential benefits of screening should a man be encouraged to make a personal decision about screening.
The views and opinions expressed in this article are those of the writer and do not necessarily reflect the views and opinions of CNN or the American Cancer Society.