Prostate Cancer Screening - the Debate Continues
Is Screening With DRE and the PSA Test Beneficial?
Sep 24, 2009
Screening for certain cancers helps detect the cancer early and decreases the chance of dying from the disease. However, evidence as to whether prostate cancer screening results in a decrease in the death rate is controversial. In March this year, results from two major prostate cancer screening trials were reported, but instead of clarifying this issue they have further fuelled the debate.
Prostate Cancer Screening Tests – the DRE and PSA Test
Screening for prostate cancer is carried out using the digital rectal examination (DRE), which involves the doctor inserting a lubricated gloved finger into the lower part of the rectum to feel for any lumps on the prostate glands. A test used alongside the DRE is the prostate-specific antigen (PSA) test. The PSA test measures the level of PSA in the blood, which is a protein found at elevated amounts in men who have prostate cancer.
Prostate Cancer Diagnosis
If prostate cancer is suspected following screening, a biopsy is carried out in order to determine if the patient actually has the disease. This diagnosis of prostate cancer requires removal of several small tissue samples from the prostate glands, which are then analysed under the microscope for the presence of cancer cells.
Why is Prostate Cancer Screening Controversial?
The PSA test is not always a reliable indication for the presence of prostate cancer - it can result in a large number of false positives, with over 60% of men who show a raised PSA level not actually having prostate cancer. Other factors that may contribute to a raised PSA include infection or inflammation of the prostate or benign prostatic hyperplasia (BPH) - an enlargement of the prostate that is not cancerous. In addition, PSA levels generally rise as men get older.
Scientists are working to improve the PSA test and also identify other molecular markers to improve screening for prostate cancer, as current methods may lead to many men undergoing biopsies unnecessarily.
Prostate cancer screening may also result in many diagnosed patients being treated prematurely for a disease where symptoms may not manifest for many years. Since most men who have prostate cancer do not die from the disease, they may undergo unnecessary treatment and be exposed to associated side effects, such as impotence and incontinence, with little chance of any real benefit.
What are Current Recommendations?
No widespread program for prostate cancer screening is in place. Nonetheless, some physicians routinely use the DRE and PSA test to screen men over the age of 50 years as well as younger men at higher risk. This is because some organisations, such as the American Cancer Society, recommend such screening. Alternatively, the US Preventative Services Taskforce recommends against screening for prostate cancer in men of all ages. Different organisations in many other countries also have various stances on the issue.
New Evidence - is Prostate Cancer Screening Beneficial?
In March this year, results from two major prostate cancer screening trials were reported in tandem in the New England Journal of Medicine. Many hoped these studies would provide the long-awaited answer to this question, but instead patients and doctors are none the wiser.
The US-based Prostate, Lung, Colorectal and Ovarian Cancer (PLCO) screening trial involved nearly 77,000 men aged 50 to 74 years who received either usual care (control group) or annual screening consisting of a PSA test for six years and a DRE for four years. The study showed that 22% more prostate cancers were diagnosed after seven years in the group of patients who were screened compared with the control group; however, there was no significant difference in the number of deaths due to prostate cancer. Preliminary results at 10 years follow up are consistent with these findings.
Alternatively, a large European screening study has suggested that prostate cancer screening does lead to a mortality benefit. The European Randomized Study of Screening for Prostate Cancer (ERSPC trial) involved 182,000 men aged 50 to 74 years, with those in the screening group offered a PSA test every four years. 39% more prostate cancers were diagnosed in the screening group compared with the control group and an overall 20% reduction in death after nine years was observed. The study did note, however, that screening with PSA was also associated with a high risk for over-diagnosis.
What’s Next?
Results of these two large screening trials have been eagerly awaited by many; however, it seems the evidence is still inconclusive. The authors of the ERSPC trial, which showed a mortality benefit, noted that “...the rates of death in the two study groups began to diverge after seven to eight years and continued to diverge further over time.” As such, further follow-up analysis for each trial may provide more conclusive evidence as to whether there are any benefits of widespread screening for prostate cancer in patients who show no symptoms of the disease. What does seem apparent, however, is that more accurate testing methods for prostate cancer screening are needed, which will also define who needs treatment and who can consider watchful-waiting.
Sources:
American Cancer Society Website, 2009; Detailed Guide: Prostate Cancer - Can Prostate Cancer Be Found Early?
Fritz et al., 'Screening and Prostate Cancer Mortality in a Randomized European Study.' N Engl J Med 2009; 360:pp1320-1328
Gerald et al., 'Mortality Results from a Randomized Prostate-Cancer Screening Trial.' N Engl J Med 2009; 360:pp1310-1319
National Cancer Institute Website 2009, Prostate-Specific Antigen (PSA) Test
Smith et al., 'The early detection of prostate carcinoma with prostate specific antigen: The Washington University experience.' Cancer 1997; 80:pp1853–1856.
US Preventative Taskforce, 'Screening for Prostate Cancer: U.S. Preventive Services Task Force Recommendation Statement' Ann Int Med 2008; 149:pp185-191
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