Vasectomy and cancer
What Doctors Don’t Tell You (Volume 14, Issue 1)
Q I had a vasectomy 19 years ago when I was 30, but I’m now beginning to worry about the prostate cancer connection. Is it really true that having a vasectomy can cause prostate cancer? If so, what can I do about preventing it? – JP, via e-mailA The prostate cancer/vasectomy connection is one of those medical controversies that seems to rumble on interminably. Ever since vasectomies first became popular about 20 years ago, there have been scores of medical studies carried out to determine whether or not vasectomy causes prostate problems.
At first, about half the studies said yes while the other half said no.
Then, in 1993, along came two major pieces of research that seemed to resolve the issue. These were a couple of huge studies involving over 50,000 men, and backed by the prestigious Harvard Medical School in the US.
The first was what is called a ‘prospective’ study, which means that the data were collected as the study continued on. Over the four-year course of the study, there were around 300 new cases of prostate cancer among the men in the study. Looking at these data, there was a 66 per cent greater risk of prostate cases among the men who had undergone vasectomy (JAMA, 1993; 269: 873-7).
The second study was ‘retrospective’ – which means that it looked at existing medical records. In this case, the Harvard researchers compared some 15,000 men who had undergone vasectomy with 15,000 similar men who had not. The results were virtually identical to those of the first study.
In brutal statistical terms, the risk of developing prostate cancer after vasectomy jumps from seven per 1000 men per year to 11 per 1000 men per year – an increase of more than 60 per cent (JAMA, 1993; 269: 878-82). The researchers confidently concluded that there was a genuine connection between prostate cancer and vasectomy, as the odds of these two findings being chance results were thousands to one against.
But the studies soon began to be questioned. In 1994, a very large-scale Danish report on every vasectomy case in Denmark over a 12-year period (nearly 75,000 men) compared their prostate cancer risk with the rest of the Danish male population – and found no connection at all (BMJ, 1994; 309: 295-9).
This fed a controversy that was kept alive throughout the 1990s with yet more conflicting studies.
The latest study so far has come from New Zealand, a country with the highest rate of vasectomy in the world – and apparently meticulous cancer records. It compared more than 900 men with prostate cancer with about 1200 healthy men, and found no difference in prostate cancer rates (JAMA, 2002; 287: 3110-5).
So, what’s the latest verdict? Recently, US epidemiologists pulled together the evidence from 22 separate studies done over the last 20 years, and came to the conclusion that there is indeed a small extra risk of prostate cancer after vasectomy. However, they’re not sure whether this is a true causal connection or due to so-called ‘detection bias’ (Prostate Cancer Prostatic Dis, 2002; 5: 193-203). If it’s the latter, it could be, for example, that prostate cancer is more readily picked up in men submitting to vasectomy because such men are more health conscious and more likely to be regularly examined by a doctor.
On the other hand, there is evidence that a vasectomy may slightly increase testosterone levels in the blood – which is important as testosterone is known to promote prostate cancer.
On balance, therefore, there may indeed be a small increase in cancer risk.