Prostate Cancer Much of the spay/neuter information available to the public asserts that neutering will reduce or eliminate the risk that male dogs develop prostate cancer. This would not be an unreasonable assumption, given that prostate cancer in humans is linked to testosterone. But the evidence in dogs does not support this claim. In fact, the strongest evidence suggests just the opposite.
There have been several conflicting epidemiological studies over the years that found either an increased risk or a decreased risk of prostate cancer in neutered dogs. These studies did not utilize control populations, rendering these results at best difficult to interpret. This may partially explain the conflicting results.
More recently, two retrospective studies were conducted that did utilize control populations. One of these studies involved a dog population in Europe5 and the other involved a dog population in America6. Both studies found thatneutered male dogs have a four times higher risk of prostate cancer than intact dogs.
Based on their results, the researchers suggest a cause-and-effect relationship: “this suggests that castration does not initiate the development of prostatic carcinoma in the dog, but does favor tumor progression”5 and also “Our study found that most canine prostate cancers are of ductal/urothelial origin….The relatively low incidence of prostate cancer in intact dogs may suggest thattesticular hormones are in fact protective against ductal/urothelial prostatic carcinoma, or may have indirect effects on cancer development by changing the environment in the prostate.” This needs to be put in perspective. Unlike the situation in humans, prostate cancer is uncommon in dogs. Given an incidence ofprostate cancer in dogs of less than 0.6%from necropsy studies7, it is difficult to see that the risk of prostate cancer should factor heavily into most neutering decisions.