Early detection of prostate cancer. Part 3
Screening
Cost per prostate-specific antigen test including labour is about $25. Even in a less populous province, such as Newfoundland, with about 50000 men between the ages of 50 and 75, annual screening would cost $1.25 million. This does not include additional costs arising from investigation of false-positive results. It is fair to state that mass screening for prostatic cancer with prostate-specific antigen is untenable.
Evaluating PSA as a screening test for diagnosing prostatic cancer is difficult because the natural history of prostatic cancer is largely unknown. When prostate-specific antigen is used in casefinding, very high rates of sensitivity and specificity are observed; Powell et al found in a group of men presenting with urinary obstruction a sensitivity of 90% and a specificity of 90%, using 10 µg/L as the cutoff value for prostate-specific antigen. In studies where PSA has been used to detect prostatic cancer in asymptomatic populations (screening), these figures are less impressive, with a false-positive rate of 67 % in one study.
Screening recommendations from professional groups
Neither the Canadian Task Force on the Periodic Health Examination (CTFPHE) nor the United States Preventive Services Task Force (USPSTF) advises routine testing for prostatic cancer; both base their recommendation on a formal appraisal of prevailing scientific evidence. The Canadian Cancer Society has not recommended screening with prostate-specific antigen. The National Cancer Institute (NCI) in the United States advises physicians:
Given the possibility of unnecessary morbidity associated with diagnosis and treatment of many such lesions, careful evaluation of prostate cancer screening is desirable. There is insufficient evidence to recommend transrectal ultrasound and serum tumour markers for routine screening in asymptomatic men.
Contrary to most cancer organizations in North America, the American Cancer Society recommends annual screening for all men older than 50 by both digital rectal examination and prostate-specific antigen. Both the American Urological Association and the Canadian Urological Association recommend annual screening for men 50 to 70 years with both DRE and PSA. The Canadian Urological Association’s recommendations were not accompanied by a presentation of supporting scientific evidence or of the process by which they were developed.