PROSTABLOG NZ: Rates of prostate cancer detected in NZ are expected to rise about 23% in the decade leading up to 2016, moving from 91 cases per 100,000 to 112.
That’s the finding of a Ministry of Health cancer projection report released late last month, but only just picked up by news media (none of whom looked in detail at prostate cancer).
Something the report calls the “burden of new cases” is expected to increase by 71% over the 2006-2016 period. This term is not explained (for the uninitiated).
Interpreting the report is something of a challenge.
The Ministry’s researchers have chosen to single out prostate cancer projections as the only ones that “could not be updated (although they have been extended), as these are based only on data up to 1984-88”.
The reason given is something they dub the “PSA effect”.
It’s hard to be sure, but this apparently means that because of a sudden upsurge of PSA testing in the late 1980s and early 1990s – leading to perhaps half of the Kiwi aged male population getting tested – there has been a massive blip in the detection statistics.
A half generation of men who would otherwise have not been detected until symptoms showed at an older age have been diagnosed “early”.
This has distorted trends to such an extent, it seems, the projection models can’t cope.
Graphs from the report, reproduced here, show the “bulge” effect. In the bottom one, the solid lines showing rates up to 2006 are extrapolated out (dotted lines) from 1986, ignoring what really happened because of PSA testing:
The Ministry says until rates return to what would have been expected “pre-PSA”, it cannot provide reliable predictions.
Despite that constraint, it has a go anyway: it concludes the rate of prostate cancer will continue to rise (presumably because of the baby boomer bulge moving through).
Confused? Join the club.
Why is prostate cancer being dealt with differently from other cancers that have been the subject of widespread screening and marketing campaigns, such as breast and cervical?
Is it because those screening campaigns were Ministry-approved, while PSA is frowned on by the Ministry because it leads to a problem – once prostate cancer is found there is no reliable way to know if it needs treatment, leading to possible over-treatment, and with it, unnecessary cost on the health system.
It would be useful to hear from epidemiologists on this, despite their inherent bias against PSA testing casting doubt on their views.
Still, they might help unravel the technicalities of the Ministry’s convoluted explanation.
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