New studies show an increase in prostate cancer – should we worry?
Posted by Mike Malone | Posted in Uncategorized | Posted on 29-06-2010-05-2008
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I’d say no.
Both studies have been published recently. The first one is published in Mumbai, India, and the second in Maryland, USA. I don’t propose to discuss the Indian study, as despite showing an increased risk, the authors conclude that due to the limitations of the study and the possibility of selection bias they could not form any definite conclusions, so they opted to recommend further research. But the Maryland study is worth looking at.
There are two ways that vasectomy / prostate cancer studies have been traditionally done. One is a medical records based study, and the other is the questionnaire type study. The medical records study always strikes me as the much sounder methodology. Get a large group of men diagnosed with prostate cancer, and then ascertain who has a vasectomy, or a large group of men with vasectomy and ask about prostate cancer – simple. Both methods have been used, and the striking thing about the results of this type of study is that they invariably conclude there is no association. The results have been repeated over a number of large records based studies over the years conducted in the US, Scandinavia and New Zealand (amongst others). The Recent New Zealand study used data from the national cancer registry, and is regarded by many as the most thorough study to date. Contrast that with the questionnaire studies that rely on self reporting data for both having a vasectomy and prostate cancer that in the main show up some form of association.
The Maryland study is a postal questionnaire study. Of the study population, 3373 men reported having a vasectomy, and 78 of them reported having prostate cancer. That equates to an incidence rate of 2.3%. There is no mention of the control group’s statistics. The 78 men were split up into age group at time of vasectomy, and any conclusions were the result of mathematical extrapolation. I personally feel that results from counting the numbers are much more methodologically sound.
One thing most prostate cancer / vasectomy studies fail to do is to compare their incidence rates with large data studies for the incidence rate in general – this study is no exception. There is a LOT of data about the incidence of prostate cancer available, so there is no excuse not to IMHO. Maryland has had a state cancer registry since 1982. As the recently published study was started in 1989, it would have made sense to me to co-operate with the state cancer registry and perform a medical records based study. The overall incidence rate In Maryland is reported in 1996 as being 157.4 per 100,000. This equates to an incidence rate of 0.16%. The black to white ratio being 1.7. Most research finds a higher incidence rate amongst black men – this data being about average.
Personally, I find the results are interesting, but for me the research asks many more questions than it answers. I question the use of a questionnaire based study when the state cancer registry would have been willing to co-operate in doing a large, records based study. I am uneasy with conclusions based on very small samples, and based in the main on mathematical extrapolations. And I also am curious as to how the researchers managed to get an incidence rate of prostate cancer over fourteen times higher than the state incidence rate.
