January 11, 2006. Arizona. I see this study as a huge piece of misinformation. They set out to prove a
point using very weak data. The time period chosen was one in which the PSA test was
just starting to be used, but not used primarily by the VA doctors. These
doctors have consistently denied the value of the PSA test. One more smoke screen
because they have no justification for the evident reduction on prostate cancer
mortality we are currently experiencing.
The study under review:
The Effectiveness of Screening For Prostate Cancer, Concato J et al. Arch Intern Med/Vol 166 Jan 9, 2006 pp 38 43
Type of study: Nested case-control
Comments: Case-control studies are usually appropriate for studying rare diseases or conditions that develop over long time. They are the quickest and least expensive studies to undertake. Prostate cancer is far from rare, but it does have a long development time.
The main problem with this type of study is that of all study methods, it has the largest number of biases or errors and it depends completely on high-quality records and the extraction process.
The authors go a long way to minimize biases, but there is no mention of how many of the patients categorized as "cases" or "controls" were in-country in Vietnam and exposed to Agent Orange, for which the military offers disability. This would definitely be a selection bias when compared to a normal population with no Agent Ornage (dioxin) exposure.
A key to a good case-control study is the selection of the control group. By use of nesting, the authors tried to minimize this problem, but it is one disadvantage of case-control as the control cohort can distort results.
Results:
PSA screening and all-cause mortality: OR 1.08; 95% CI, 0.71
1.64; p = 0.72
PSA and/or DRE screening and cause-specific mortality: OR 1.13; 95% CI, 0.63
2.06, p = 0.68
Comments:
These odd ratios have such a wide range that the result is bad probabilities (p = 0.72 and 0.68).These results are associated with both the case and control cohorts, the time of diagnosis, the amount of comorbidities and last but not least the extent of disease at diagnosis.
These patients are far from what the average patient diagnosed today. The question is then: How relevant is this study for today's patient? In their conclusions, the authors seem more concerned with the enforcement of informed consent than with their results which indicate a higher risk of mortality for
Study comments: The authors acknowledge the value of randomized studies but defend their use of the case-control method as valid. At the same time they fail to mention the observed reduction in mortality rate since the inception of PSA testing. They also fail to properly mention the results of the Tyrol experiment that are in direct opposition to their weak results. Nothing was mentioned on the latest updates of Scandinavian studies in which treatment resulted in a survival benefit.
They make no attempt to associate mortality and the form of treatment (or non-treatment -- "watchful waiting"). The diagnosis and deaths are defined as 1991 to 1995 for diagnosis and 1991 to 1999 for deaths. These are overlapping periods. This means that for some men, deaths occurred soon after diagnosis, indicating that possibly many of these men had advanced disease.
The authors have gone out of their way to minimize biases, but there is a previous bias on the part of these authors by way of their repeated efforts to prove the lack of efficacy for screening with PSA for prostate cancer. Many have written or co authored negative papers on this issue before.
In summary, this paper is more about promoting the recommendation of the American College of Physicians than to effectively disprove that screening with PSA and DRE results in finding earlier cases of the disease and provides an option for treatment at a time of disease progression when it is potentially more treatable.
The fact that there is no mention of a relation between PSA testing inception and the reduction in real deaths from prostate cancer is disturbing and demonstrate a reluctance of these authors to admit that providing choice has had an effect in managing the disease.
Ralph Valle, a chemist, lives in Arizona. Ralph writes on Prostate Problems Mailing List and WRITES AND LEADS CHATS WITH PRostate Help Mailing List. He volunteers for ACS and Chairs Arizona chapter of US Too!
Related
Screening for Prostate Cancer May Not Reduce Men's Risk of Dying from the Disease, New England VA Study Says Jan 11 2006
