Big Harvard Study Finds Vasectomy-Cancer Link

A newly published study from the Harvard School of Public Health has found a link between having a vasectomy and an increased risk of developing more serious forms of prostate cancer.

Researchers examined the medical records of 49,405 American men who participated in the Health Professionals Follow-Up Study, which spanned more than two decades in some cases. (The Health Professionals Follow-Up Study is the male counterpart of the Nurses' Health Study, a long-term women-only health study also organized by Harvard.) What they found was that men who had had a vasectomy had an increased chance of developing advanced or lethal prostate cancer.

Numbers in perspective

During the course of the Harvard study, 6,023 cases of prostate cancer were diagnosed, 811 of them lethal. One quarter of the men in the study reported that they'd had a vasectomy. In real-world terms, here's what the researchers found:

  • In the Harvard study, 16 in every 1,000 men in the general population developed lethal prostate cancer.
  • The study found that that number goes up to 19 in 1,000 men among those who've had a vasectomy.

In other words, the study found men who have had a vasectomy were found to be 19% more likely to develop lethal prostate cancer than men who did not. The study also showed that men who had a vasectomy were 20% more likely to develop metastatic cancer (cancer that spreads to other parts of the body).

That difference (the increase of 3 more men in 1,000 developing lethal prostate cancer) means that men who'd had vasectomies were more at risk of lethal prostate cancer than the general population, but the risk is still quite small (less than 2 percent of the population is affected). The increase in risk for advanced (that is, metastatic) prostate cancer was almost the same. Men in the study who'd had vasectomies had no increased risk of low-grade prostate cancer.

Prostate cancer in the US

According to the National Cancer Institute (NCI), about 15 percent of American men will be diagnosed with prostate cancer at some point in their life.That makes prostate cancer is the most common form of cancer and the second-deadliest form of cancer in the U.S. after lung cancer. According to the NCI, 233,000 new cases of prostate cancer will have been diagnosed in the United States in 2014, and about 29,480 men will die from the disease.

There is no consensus on whether men should routinely have a PSA (prostate-specific antigen) test to screen for prostate cancer — organizations are divided on the issue. The American Urological Association, for example, no longer recommends PSA screening for men under the age of 55 who are at average risk. The American Cancer Society says that in men at average risk, "the discussion about screening" should begin at age 50.

Causes yet to be determined, but some possibilities

It's not yet clear what might cause the increased risk of advanced and lethal prostate cancer among men who've had vasectomies, and that will certainly be the subject of further research. Researchers will certainly want to determine whether the procedure itself creates some sort of mechanism that leads to cancer formation.

Another hypothesis that researchers are likely to look into is that men who have a vasectomy are often far less likely to use condoms, and if they have multiple sexual partners, not using condoms puts them at greater risk for sexually transmitted diseases. Some studies have suggested a link between human papilloma virus (HPV) and prostate cancer, although that matter is far from settled. The Harvard researchers looked at data on HPV and other sexually transmitted diseases in their study and concluded it wasn't a factor. Scientists will no doubt continue to investigate that link, however.

Other interesting findings

Interestingly, the researchers found that the increase in risk seemed to be even more acute in men who had their vasectomy when they were younger than 38.

Among another subgroup of men in the study who received regular PSA tests to screen for prostate cancer, having had a vasectomy was associated with a 56% increased risk of lethal prostate cancer. Naturally, that doesn't mean that PSA tests increase the risk of cancer. It's possible, however, that those men were already at higher risk of prostate cancer for other reasons, such as age or family history of prostate cancer, and that may be why they were being followed closely. But the statistical association between vasectomy and serious prostate cancer is significant enough that it will definitely warrant further study.

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