NZ CANCER SOCIETY – POSITION STATEMENT: Screening for Cancer of the Prostate – November, 1999
Although prostate cancer is a major health problem for older men, current methods of screening for this cancer have not been proven to reduce the number of men who die from this disease.
For this reason, and because of the risks associated with screening, the Cancer Society does not recommend the testing of men who do not have symptoms.
The Society will review its position when the results from current randomised controlled trials for prostate screening are reported. In the meantime, the Cancer Society recommends that men considering screening be informed of its lack of proven benefit and of the potential risks.
The Society also recommends that men with prostate symptoms be assessed by their doctor.
Prostate cancer is the leading cancer registered for men in New Zealand, with the rate of registration having almost trebled since 1990.
This increase is linked to changes in cancer reporting and diagnosis, the latter being due to more men having prostate specific antigen blood tests ( PSA).1
Prostate cancer occurs mainly in men over the age of 60, with 80% of cases occurring in men 65 and over. At present it is the third leading cause of male cancer death.
Because we don’t know the causes of prostate cancer, prevention is not possible.
There is increasing interest in the potential of screening for prostate cancer to detect the disease at an early, more curable stage. Screening is the testing of people with no symptoms to identify early signs of disease.
Screening differs from the diagnosis of people seeking help for symptoms in that the process is offered to well individuals, either direct or through publicity.
There is an ethical obligation among those offering screening to ensure there is conclusive evidence that it will benefit a significant proportion of those who are screened.
Evidence of benefit
Various screening tests for prostate cancer are being trialled. These include digital rectal examination (DRE), trans-rectal ultrasound and PSA (prostate specific antigen) testing.
Randomized controlled trials (RCTs) provide the best evidence to support any method of cancer screening. In an RCT for screening, people in a population are randomly allocated into two groups, usually called the study and control groups. One group is offered screening and the other is not. The results are assessed by comparing rates of death from the disease in those offered screening with those who are not.
As yet there is no evidence from RCTs to show that screening is effective in reducing deaths from prostate cancer. Two RCTs for prostate screening are underway, however, and results from these studies are likely to be reported in the next five years.
A man’s chances of developing prostate cancer increase as he gets older. The chance of having prostate cancer which remains latent and has no symptoms also increases with age.
Prostate screening can therefore result in the detection of innocuous, occult disease which would never have developed into a detectable cancer. Treatment of such asymptomatic cancers can have adverse effects, such as urinary incontinence and impotence.
The results of prostate screening tests can be inaccurate, resulting in both false positive and false negative results. Examination by DRE is subjective and its accuracy depends on the experience of the clinician.
Also, many tumours of the prostate gland cannot be felt and therefore will be missed by DRE.4
One of the disadvantages of PSA tests is their low specificity,5 resulting in many patients requiring further investigation which will eventually show no cancer.
There is no clear evidence that early detection and treatment of prostate cancer results in increased life expectancy or improved quality of life for men who have prostate cancer.
As the incidence of prostate cancer is greatest among men in the oldest age groups, where any possible extension of life following screening is likely to be short, research is needed to assess the quality of life years that may be gained as well as harms and benefits.
Recommendations for screening
There is currently no evidence from randomised controlled trials that screening is effective in reducing mortality from prostate cancer and because of the risks associated with screening, the Cancer Society of New Zealand does not recommend screening for prostate cancer .
Other agencies which do not recommend screening include the government’s National Advisory Committee on Health and Disability, the Australian Health Technology Advisory Committee, the Australian Cancer Society, the US Preventive Services Task Force, and international health agencies such as the World Health Organization and the International Union Against Cancer
Men who have a first degree relative (father or brother) who developed prostate cancer may have a two to three fold risk of developing prostate cancer.11 The risk rises if two or three first degree relatives have had prostate cancer, particularly before the age of 65.
The Cancer Society of New Zealand recommends that for these men screening should be an informed choice. They should be informed of the potential risks and lack of proven benefit.
Although the Urological Society of Australasia does not recommend population screening of asymptomatic men for prostate cancer, it advises that men who wish to be tested should be able to do so, after appropriate counselling regarding the potential risks and benefits of investigations and the controversies of treatment.
The Urological Society also advises that an individual doctor should decide whether to advocate testing in a man not requesting it.
While agencies such as the American Cancer Society and the American Urological Association recommend that physicians offer PSA and DRE testing to men 50 years and older who have a life expectancy of at least 10 years, and to younger men who are at high risk, they stress the need for them to provide men with adequate information regarding the potential benefits, side effects and uncertainties regarding early prostate cancer detection and treatment, so that men can make informed decisions about testing.
The Cancer Society of New Zealand recognises that prostate cancer is a major health problem among older men, and it will review its position when data from current randomised controlled trials become available.
In the meantime we recommend that men who have no symptoms should be informed of the potential risks as well as the lack of proven benefit that it will reduce their chances of dying from prostate cancer before undergoing a test for prostate cancer.
The Cancer Society also recommends that men with symptoms suggestive of benign or malignant prostatic disease should seek an assessment by their doctor.