I have no idea what joinpoint analysis is; however, there is a recent
article and accompanying editorial on some problems in using prostate cancer
death statistics to estimate the effect of PSA screening : Newschaffer CJ et
al., 2000, J Natl Cancer Inst 92:613-21; and Albertsen P, Ibid, pp 590-1.
One thing to keep in mind as these statistics come in and are analyzed over
the next few years is that any decrease in prostate cancer mortality caused
by PSA screening is only half of the picture. The other half is the number
of false positives treated, and the amount of unnecessary morbidity this
causes. We could get rid of virtually all prostate cancer deaths by simply
prophylactically removing (or irradiating) every man's prostate at age 40.
But at what cost (in harm as well as financially)? The number of false
positives is especially hard to calculate for prostate cancer, because it is
not false positives in terms of actually having prostate cancer that is of
interest, but false positives in terms of prostate cancer that would have
ever become clinically significant. There is really no question that PSA
screening will lower the prostate cancer death rate. That is a foregone
conclusion for removing and obliterating more prostates. The main question
is the benefit-harms tradeoff. No report of lower prostate cancer death
rates due to screening should be let off the hook without addressing this
question.
We recently completed an elaborate cost-effectiveness analysis of PSA
screening using the sensitivity of the assay for clinically significant
prostate cancer as estimated prospectively by Gann et al., 1995 (JAMA
273(4):289-94). As expected, our model estimated a substantial decrease in
prostate cancer deaths; however, this benefit appreared to be largely
cancelled out by the large number of false positives and the consequent
quality-of-life loss that resulted.
David L. Doggett, Ph.D.
Senior Medical Research Analyst
Technology Assessment Group
ECRI, a non-profit health services research organization
5200 Butler Pike
Plymouth Meeting, PA 19462-1298, USA
Phone: +1 (610) 825-6000 ext.5509
Fax: +1(610) 834-1275
E-mail: [log in to unmask]
> -----Original Message-----
> From: Jeanne Lenzer [SMTP:[log in to unmask]]
> Sent: Monday, May 22, 2000 12:14 PM
> To: EBM (E-mail)
> Subject: Joinpoint analysis & prostate cancer
>
> The National Cancer Institute just announced that "screening and/or
> treatment" is responsible for downward trends in prostate cancer deaths.
> This seems like a real stretch to me and I need help because they are a
> term and technique terms I don't understand.
>
> First, to me, it seems that a downward trend in prostate cancer morbidity
> and mortality could simply be due to a cohort effect, another possibility
> is "detections effect" in which skyrocketing increases due to better
> detection begin to taper off as more and more men have had PSA testing so
> fewer cases may be detected causing both a false initial increase in death
>
> rates and then a slowing of death rates.
>
> But they stumped me when they said they arrived at their conclusions using
>
> a "new statistical technique" called "joinpoint" analysis in which they
> look at segments of time rather than overall trends. Come again? can
> someone help me out here? This doesn't sound anything like proof of
> effect
> to me. Or am I nuts? Why are "segments" in time being used instead of
> overall trends? Were regions in which there is a high rate of screening
> and treatment compared with regions with four-fold variations of the same?
>
> Jeanne
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