Before discussing any real or perceived association between vasectomy and prostate cancer, it’s important to be aware of the general incidence and risk factors of prostate cancer in all men–vasectomised or not. It’s also important to understand why the prostate cancer / vasectomy debate came to be, what the evidence is for and against any causal link, and why the myth still persists in cyberspace today. This article looks at the history and the evidence as well as giving you a general overview of the incidence and risk factors known to be associated with prostate cancer.
Prostate cancer incidence and risk factors
The table on the left lists the most common cancers diagnosed annually in the US.2 The same data set indicates that despite the fact that prostate cancer is the most frequently diagnosed cancer for men, it’s by no means the biggest killer:-
- Despite the fact that you are 10% more likely to be diagnosed with prostate cancer, you are over 5 times more likely to die of lung cancer than prostate cancer
- You are 43% more likely to be diagnosed with prostate cancer than colon cancer, yet more likely to die from colon cancer by over 50%.
According to Cancer Research (UK), men are much more likely to die with prostate cancer than from it. As demonstrated by the graph (left)1, the strongest risk factor is simply getting older.
- Very few cases are registered in men under 50
- More than 60% of cases occur in men over 70 years old
- The largest number of cases is diagnosed in the 70-74 and 75-79 age groups
- About one third of men over 50 have a small focus of cancer in the prostate
- This rises to approximately 50% by the age of 80
- Only 1 in 25 men (4%) will die from prostate cancer
Where you live plays a big part in prostate cancer. The USA has the highest incidence of prostate cancer, and the far east has the lowest as shown left2. Why this should be the case is down to a combination of factors including ethnicity, lifestyle and diet factors.
African-American men have the highest incidence of prostate cancer. Higher than white Americans by some way, and Asian men have the lowest incidence1.
If you have a family history of prostate cancer, you have an increased risk. If your relative is a father or brother, affected at a young age or more than one relative has been affected then your risk increases by up to three times. Men whose families have an increased risk of breast cancer are also at higher risk of prostate cancer1.
Although Japanese men are amongst the least likely to develop prostate cancer, if they move to the west and change diet, their risk factor increases dramatically. The high intake of animal fat in the western diet is a key factor. Pork and red meats especially increase risk. As does meat cooked at high temperature, or meat cooked on the barbecue1. A high dairy consumption also elevates the risk factor. A diet rich in fruit and vegetables and fish lowers risk.
Moderate consumption of beer and wine is not linked to an increase in prostate cancer risk, but moderate consumption of spirits, and binge drinking is. Heavy drinking increases risk.
Although most studies conclude that men who smoke do not have an increased likelihood of developing prostate cancer, some research suggests that smokers are more likely to die of the disease than non-smokers3.
Do cancer organizations regard vasectomy as a risk factor?
In a word, no. Cancer Research UK, and the US National Cancer Institute and the World health Authority all mention the past research and all conclude that whilst they continue to look at new research, past studies have not demonstrated a causal link between vasectomy and prostate cancer, nor any form of biological explanation.
History of the myth
Some early studies looking into testosterone levels in men found that vasectomised men had higher levels of testosterone later in life than non-vasectomised men. High levels of testosterone are associated with an increased risk of prostate cancer. These studies, combined with other vasectomy and cancer studies done in the late 1980’s prompted researchers to look into the question of if there was a causal link between vasectomy and prostate cancer. The biggest studies done into the question were by Giovannucci et all, and published in May 19925 and February 19936.
The methodology of these studies is worth a close look. In 1976 and 1978, questionnaires were sent to married women in 11 states who participated in a study to look at methods of birth control used and associated health factors. 14,607 of the women reported vasectomy as the couple’s primary form of contraception. In 1989, the authors contacted these 14,607 women and matched them with 14,607 participants whose husbands had not had a vasectomy prior to 1978. At no point did the researchers check if the data coming back was accurate. The researchers did not cross check that the men had a) prostate cancer or b) a vasectomy.
The same data was used to publish both studies. The first study looked at the causes of death of men in the study. The study found that men with a vasectomy were less likely to die from the causes they examined than non-vasectomised men. The study concluded that “Our study also found no increase in overall mortality from cancer after vasectomy, but there was an apparent increase in the risk of cancer 20 or more years after vasectomy that requires further study”.
Bring on study number 2. Rather than set up a new study to look into the question they had asked, they simply regurgitated the results of the same data set in a different format. It’s worth repeating the fact that the researchers did not actually cross check that the men had indeed had a vasectomy or prostate cancer. The data relied entirely on random responses to a questionnaire sent to married women. The numbers add up as follows:-
- The study base consisted of 14,607 women who said their husband had had a vasectomy, and 14,607 women who said their husband hadn’t had a vasectomy.
- 96 new cases of prostate cancer were diagnosed in the study base.
The authors of the study concluded from the above data that men with a vasectomy 20+ years had an increased relative risk of prostate cancer. 96 cases is not a lot of data to base such sweeping statements on, being statistically a very small sample. In addition, it’s possible that half of the 96 cases hadn’t had a vasectomy as the sample was half men who had vasectomy and half who hadn’t. As the authors don’t publish a breakdown, it possible that the results were based on 48 men or less.
Remember that by the age of 50, a third of all men have prostate cancer to some degree. The study did not compare the results they had observed to national trends. In fact, had they done so they very well may have found that their results merely mirrored the national trend. Many researchers think that this study provides the strongest evidence for a link between prostate cancer and vasectomy. It grabbed the headlines at the time, and it’s certainly the one many people continuously refer back to even today.
That study, and a few other less convincing studies constitute the case for the link. What about the evidence against?
Firstly, many of the studies that find in favour of the possibility of a link do not stand up to objective analysis. The study above according to one peer7 in 1993 said that “Giovannucci’s detractors argue that the study is simply a dangerous attack on an already underused contraceptive method and that the report is fueled more by hunger for media attention than by sound science. Supporters counter that the findings are being carelessly dismissed to protect vasectomy in the US.”
In March 1993, The NICHD and National Cancer Institute convened a conference to clarify the available evidence on the relationship between vasectomy and prostate cancer. Scientists reviewed and carefully weighed all of the data available at that time, including results from published and unpublished studies. They determined that the results of research on the association between vasectomy and prostate cancer were not consistent. In addition, the scientists could not find any convincing biological explanation for a link between vasectomy and an increased risk of prostate cancer. In 1997, the National Cancer Institute convened the prostate cancer Progress Review Group (PRG), a committee that included members from the scientific, medical, industrial, and advocacy communities. This group was charged with developing a national plan to outline scientific efforts involving prostate cancer research. The PRG’s final report, published in August 1998, concluded that the evidence supporting a role for vasectomy in the development of prostate cancer is weak.
Researchers continue to investigate the possible relationship between vasectomy and prostate cancer. The majority of studies conducted thus far have upheld the conclusions made at the 1993 NICHD conference. Although a few studies have reported a link between vasectomy and prostate cancer, it is possible that other factors, including chance, may be responsible for the association suggested in these studies.8
Since 1993, researchers have been keen to avoid the mistakes made by Giovannucci. Very few studies now rely on unchecked questionnaire data. Many of the more recent studies are done by selecting patients on the grounds of one or more factors are verifiable by medical records. Also, detection bias is something researchers are keen not to repeat. It’s always possible that detection bias exists in all studies, but researchers are aware of the problem and design studies so that the effects are minimised.
There have been quite a lot of well designed, large studies that categorically refute the findings of Giovannucci. I’m going to mention just two. Firstly, a study published in 2002 that looked at 585 prostate biopsies of men with and without vasectomy9. It concluded that “We found no increase in prostate cancer incidence or severity in patients referred for prostate biopsy who had undergone prior vasectomy. In fact, prostate cancer was less common with fewer poor prognostic indicators in patients with previous vasectomy. These findings may be secondary to either selection bias, as patients with a vasectomy may seek more routine medical care, or a greater tendency of primary providers to refer these patients for evaluation.”
The second, and probably most significant study to discuss is the New Zealand study published in 200210. The reason this study has proved to be the strongest evidence against a possible link is the fact that it was designed to have a very robust methodology. New Zealand was chosen for the study in part because NZ has one of the highest uptakes of vasectomy in the world, but mainly because the key factors can be checked with medical records. New Zealand has a National Cancer Registry, and all new cases are noted to, and followed up by the registry. The participants of the study were all new cases of prostate cancer taken from the national Registry, had to be on the electoral roll and have a traceable telephone number. Medical records were examined in addition to the data from the National Cancer Register, and in 100% of the cases that were checked, vasectomy was confirmed by medical records. The study’s purpose was not revealed to participants, and interviewers were not aware of if they were interviewing a man who had a vasectomy or not. Key results of the study were:-
- Although many men are diagnosed and treated for prostate cancer as outpatients, the cases for this study came from the entire population through statutory notification of cancers by all pathology laboratories. Response rates for both cases and controls were high, minimizing the possible effects of selection bias.
- Pathological review of a sample of diagnostic specimens confirmed the diagnosis of prostate cancer.
- Similar proportions of cases (9%) and controls (10%) had a vasectomy 25 years or more previously, representing 38% of all men with a vasectomy.
- No elevation in risk was found 25 years or more after vasectomy, even though 38% of men with vasectomy were in this group.
- The risk of prostate cancer after vasectomy was not increased for any age at vasectomy.
- The risk of prostate cancer from vasectomy was not appreciably different among men with or without a family history of prostate cancer.
- No trend in relative risk with years since vasectomy was apparent.
Why does the myth still exist today?
By and large, in the real world it doesn’t. Since the start of the scare, and over the last 25+ years various medical authorities have looked at the issue. The World Health Authority, the American Urological Association, the Royal College of Obstetricians & Gynaecologists, the National Cancer Institutes of the US, UK, New Zealand, Scandinavian and other countries have all commissioned large scale well designed studied. The studies have been peer reviewed several times, and conclusions drawn. Whilst there is no conclusive evidence that a causal link might exist, there is plenty of overwhelmingly conclusive evidence that a link does not exist. Whilst looking at any new studies that emerge, the medical world has long since regarded the issue as a closed case and moved on. The World Health Authority have long since been recommending that men with vasectomy are not screened for prostate cancer any more frequently than non-vasectomised men are.
The myth exists primarily in cyberspace–not the real world. There are various individuals and groups that are opposed to vasectomy for a variety of reasons, including religious beliefs and the desire to sell various self-published books. Basically, as cancer is a scary word it’s used as the primary reason not to have a vasectomy in the place of any real argument. Scare tactic–pure and simple. The Giovannucci et all study is frequently referenced.
How you can lessen your risk factor
Obviously some of the risk factors such as being old, your ethnicity and family history you can’t do anything about. Nor will the decision to have a vasectomy or not affect your risk of prostate cancer. However, there are simple things you can do to lower your risk. Obviously giving up smoking is a good start. I know–easier said than done, but you know the risk, and remedy. Alcohol in moderation is OK, but cutting down is never a bad thing. The main thing you can do is to change your diet for a healthier one. Eat five portions of fruit and vegetables a day, and lowering the amount of meat and dairy in your diet are common recommendations. The other major change you can make is to increase your intake of Lycopene. This is a naturally occurring antioxidant that is known to reduce the risk of all cancers for both men and women. It can reduce your incidence risk of prostate cancer by up to 33%4. Cooked tomato products contain large concentrations of Lycopene, and the Lycopene is in a form easiest for the body to digest and use.
2 Data was taken from the American Cancer Society, and represents the number of new cases diagnosed in 2002.