After vasectomy, the testes continue to make sperm. When the sperm cells die, they are absorbed by the body,
much like unused sperm in a nonvasectomized man. Nevertheless, many vasectomized men develop immune
reactions to sperm, although current evidence indicates that these reactions do not cause any harm.
Ordinarily, sperm do not come in contact with immune cells, so they do not elicit an immune response. But
vasectomy breaches the barriers that separate immune cells from sperm, and many men develop anti-sperm
antibodies after undergoing the procedure. This has given rise to concern on the part of doctors and
researchers, because immune reactions against parts of one's own body sometimes cause disease. Rheumatoid
arthritis, juvenile diabetes, and multiple sclerosis are just some of the illnesses suspected or known to be caused
by immune reactions of this type.
Immune reactions can also contribute to the development of atherosclerosis, the clogging of arteries that leads
to heart attacks. In the late 1970s, after a study of 10 monkeys showed an increased risk of atherosclerosis in
vasectomized animals, doctors became concerned that vasectomy might increase the risk of heart disease in
men.
Other, more persuasive research results, however, indicated that these concerns were not warranted. In
particular, the HSAM study provided a high level of reassurance. Researchers conducting this study found no
evidence that vasectomized men were more likely than others to develop heart disease or any other immune
illnesses.
But just as concerns about heart disease and immune ailments following vasectomy were being laid to rest,
worries about prostate cancer were taking their place.
Although the HSAM and a number of other studies showed no increase in cancer among vasectomized men,
three separate hospital-based studies published in 1990 reported positive correlations between vasectomy and
prostate cancer. However, a well-regarded 1991 study found no such relationship.
Because of the importance of the issue, all of this research has been carefully analyzed, and scientists have
identified several potential problems in the studies. It is possible, for example, that men who choose vasectomy
for contraception have above average access to health care. In particular, these men may be more likely than
others to visit urologists--physicians whose specialty includes the male reproductive organs, and they might
thus be more likely to receive an accurate diagnosis of prostate cancer, a disease that often causes no
symptoms and remains undiagnosed. If this were the case, vasectomy might falsely appear to increase the risk
of this cancer.
In October 1991, the World Health Organization (WHO) sponsored a meeting of experts from around the world
to evaluate the available evidence regarding a link between vasectomy and prostate cancer. Because additional
concerns had been raised about a possible association between vasectomy and testicular cancer, evidence for
such an association was also weighed at the meeting. The assembled experts concluded that a causal
relationship between vasectomy and cancer of either the prostate or testis was unlikely. This conclusion was
based in large measure on an overview of study results. But it was strengthened by the absence of a biological
explanation of how vasectomy might product any form of cancer.
Following the WHO meeting, two additional studies of vasectomized men found no increased risk of either
prostate cancer or all cancers combined. Subsequently, a study conducted in three regions of the United States
suggested that the subgroup of men who had a vasectomy before age 35 might have a slightly increased risk of
developing prostate cancer. However, the size of this subgroup was not large enough to make the result
conclusive. The study did not find any increased cancer risk in men who underwent vasectomy after age 35.
In 1993, a noted team of Harvard epidemiologists published findings from two large studies in the Journal of the
American Medical Association (JAMA). One of these studies was retrospective (backward-looking), while the
other was prospective and followed new patients. Both found vasectomy to be associated with a moderately
elevated relative risk of prostate cancer that increased with time after the procedure. After more than 20 years, a
vasectomized man appeared to be twice as likely to develop prostate cancer as a nonvasectomized man of the
same age. Although this conclusion may seem startling, scientists generally consider risk findings of this
magnitude to be of doubtful significance.
The studies were examined by experts in several professional organizations as well as in a JAMA article. The
authors of this article concluded that the studies could neither be relied upon nor ignored and that further
research was essential.
These authors pointed out that, since the causes of prostate cancer remain unknown, it had been impossible to
assure that risk factors for the illness were equally distributed between the vasectomized and nonvasectomized
men. In one of the studies, the men who had undergone vasectomy had a lower overall death rate than the men
who had not, supporting the likelihood that the two groups had different characteristics. Differences of this
type might have affected prostate cancer risk, producing study results that misleadingly implicated vasectomy
as a cause of prostate cancer.
Like others before them, these scientists also noted the lack of evidence for any biological mechanism that
could link vasectomy with prostate cancer.
In 1993, NICHD convened a meeting at which an expert panel considered published data, preliminary results
from studies in progress, and an analysis of eight epidemiologic studies, including the two reports mentioned
above. The panelists concluded that the positive associations between vasectomy and prostate cancer found in
some studies might or might not be valid. Scientists agree, however, that if any increased risk is caused by
vasectomy, it is relatively small.
WHO is currently conducting a major study of vasectomy and prostate cancer in several developing countries,
and three other studies are ongoing in the United States and Canada. Scientists expect these investigations to
help resolve the issue.
In the interim, most physicians will be guided by NICHD's expert panel of 1993 which concluded there is
insufficient basis for recommending any change in current clinical or public health practice. Providers should
continue to offer vasectomy and to perform the procedure, the panel said. Vasectomy reversal is not warranted
to prevent prostate cancer, and screening for prostate cancer should not be any different for men who have had
a vasectomy than for those who have not undergone the procedure.
Vasectomy has been used for about a century as a means of sterilization. It has a long track record as a safe and
effective method of contraception and is relied upon by millions of people throughout the world. On the basis of
much evidence, experts believe that vasectomy can safely continue to be used as it has been in the past, while
further research is carried out.
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