Controversy regarding the use of PSA (prostate-specific-antigen) in early detections of prostate cancer continues with the recent publication of an article in the New England Journal of Medicine (NEJM).
Prostate cancer is the most frequent cancer and the second leading cause of death from cancer in men, exceeded only by lung cancer. In 2008, an estimated 24,700 men were diagnosed with prostate cancer and 4,300 died of the disease.
The walnut size prostate gland lies below the urinary bladder in front of the lowest inch of the rectum, through which it can readily be felt on digital rectal examination (DRE). The gland has an important role in the proper flow of urine. It also provides the proteins and ions that form the bulk of the semen. In conjunction with other smaller glands in the vicinity, the prostate gland produces secretions that serve to lubricate the reproductive system and provide a vehicle for storage and passage of sperms.
Once upon a time, “the old finger” i.e. DRE was the only crude way to pick up early prostate cancer. Although DRE has a cancer detection rate of only 0.8 to 7.2 percent, it remains an important test that can be done easily in a doctor’s office. It also checks for anal and rectal tumours.
The PSA test was introduced in North American medical practice by the end of 1980s. PSA was expected to replace the embarrassing and uncomfortable DRE. And it was promoted as an ideal test for screening and early detection of prostate cancer. But this hope has not materialized. PSA blood test has a false positive rate of 20 to 50 percent and false negative rate of 25 to 45 percent. That means 30 to 50 percent of the time the test is wrong.
The editorial in the NEJM says, “In the United States, most men over the age of 50 years have had a prostate-specific–antigen (PSA) test, despite the absence of evidence from large, randomized trials of a net benefit. Moreover, about 95 per cent of male urologists and 78 per cent of primary care physicians who are 50 years of age or older report that they have had a PSA test themselves, a finding that suggests they are practicing what they preach.”
Recent clinical trials have shown that PSA screening without DRE was associated with a 20 per cent relative reduction in the death rate from prostate cancer at a median follow-up of 9 years, with an absolute reduction of about 7 prostate cancer deaths per 10,000 men screened. Critics say that this is at best a modest effect on prostate cancer mortality and the benefit comes at the cost of substantial over-diagnosis and over-treatment. There is net harm compared with potential benefits.
Experts agree that PSA testing is an imperfect screening tool. They say the test is as effective as programs such as mammography for breast cancer and fecal occult blood testing for colorectal cancer.
The Canadian Cancer Society recommends that men aged 50 and older discuss the benefits and risks of PSA testing with their physician, and the society does not plan to change its recommendation based on recent research.
Start reading the preview of my book A Doctor's Journey for free on Amazon. Available on Kindle for $2.99!