Should Canadians be offered systematic prostate cancer screening?

Severity of disease

The severity of prostate cancer is undeniable. Every year in Canada, some 20 000 new cases are diagnosed, and 20% of these men die from prostate cancer. These numbers are comparable to the numbers for breast cancer, and mortality and health care costs will increase proportionally with the rapid increase in life expectancy.

Effective method of detection

Prostate cancer screening is now possible thanks to a combination of the prostate specific antigen (PSA) test, which helps to identify those at greater risk of cancer, and development of a biopsy procedure guided by trans-rectal ultrasound. Approximately 6% of men aged 50 and older will have PSA levels higher than 4 μg/mL, and 16% will have levels between 2.5 and 4 μg/mL. Ultrasound-guided biopsies are well tolerated under local anesthetic and have a specificity of nearly 100% and a sensitivity of about 85%. About 15% of cancers are detected during a second biopsy.2

Efficacy of treatment

The efficacy of treatment for prostate cancer is well documented. A Swedish study3 demonstrated that surgical treatment of localized prostate cancer had reduced cancer mortality by more than 50% at 10 years and had had no negative effects on quality of life. No other cancer treatment can claim these results. Several other studies and observations show that screening significantly reduces mortality from prostate cancer. A study conducted in the Tyrol4 reported a statistically significant decrease in mortality among men who agreed to at least one systematic screening compared with men in other parts of Austria who were not screened. In Quebec city, a 67% decrease in mortality was observed among 7155 men (23% of 30 958 who were offered screening) who were systematically screened compared with those who turned down screening.5 Another European randomized pilot study of 2367 men showed a 75% decrease in cancer mortality at 10 years.6 We have also seen close to a 25% decrease in prostate cancer mortality in both Canada and the United States as well as in England, Austria, and several European countries since the PSA test was introduced, despite an increase in longevity.7 Regions in which the PSA test is used less extensively, such as Scandinavia and Australia, continue to experience an increase in prostate cancer mortality.

Comparison with screening for other diseases

While prostate cancer screening was being made available, screening for several other cancers was introduced on the basis of similar, even inferior data. For example, systematic screening for cervical cancer was implemented on the basis of similar observations and was never subjected to controlled studies.1 Among the many studies that have evaluated the efficacy of breast cancer screening, only 1 Swedish study was able to demonstrate a significant reduction in mortality and only in women older than 50. Breast cancer screening, however, is widely practised. The same is true for colon cancer; only 1 American study has demonstrated the efficacy of fecal occult blood screening. Even though studies are still trying to evaluate the efficacy of colonoscopy at the present time, it is widely used for screening purposes.

So, why isn’t screening for prostate cancer being promoted by family physicians as strongly as screening for these other cancers?

Clearly, advocacy for cancers specific to men has been much less effective than advocacy for cancers specific to women or cancers that affect both men and women. The biggest objection to prostate cancer screening is the potential detection of cancers that are not clinically significant and that will not result in death. It is becoming increasingly evident that low-grade cancers (Gleason =6) with a PSA of <10 carry a low risk of death, even without treatment.8 In Canada, close monitoring is increasingly recommended for this type of low-risk cancer.9 Moreover, this type of cancer seems to respond to hormone therapy and changes in diet and lifestyle, areas in which family physicians should play a predominant role. It would make sense to try to minimize the psychological and medical effects of a diagnosis of low-risk prostate cancer rather than to deprive some men of an effective means of detecting and treating a high-risk cancer just because we are afraid of adversely affecting a whole lot of other men.