Evidence Update- Neutering and Cancer Risk in Danish Dogs

10 Responses to Evidence Update- Neutering and Cancer Risk in Danish Dogs

1. Kelly says:

   March 13, 2015 at 8:52 pm

   ok – You summarized the Danish study stating: “This study is in general agreement with some of the previous research in suggesting neutering may increase the risk of some specific cancers . . .” But that doesn’t jibe with the abstract – which states that “distribution of malignant neoplasia” was [greater] in “intact” males (38%) and females (32%) vs neutered (12.5% and 17.5% respectively); so either the data from the Danish study was flipped, or the Danish study seems to contradict all (most) of the other studies. Yes, I see in the abstract where neutered females are more likely to get some forms of specific cancers, but that also seems to contradict the overall study.

   What did I miss here? I’ve read it 20 times now and come to the same conclusion .
2. skeptvet says:

   March 13, 2015 at 9:21 pm

   The the vast majority of dogs in Denmark are intact, and the numbers that indicate more neoplasia in intact dogs are not corrected for the proportion of the population intact and neutered. The overall number of cancers are greater in intact dogs because there are a lot more intact dogs, but the relative rate of occurrence of some cancers (corrected for the proportion of the population intact and neutered) is greater in neutered dogs.
3. Deborah Cottrell says:

   March 14, 2015 at 4:30 pm

   I was about to say the exact same thing as Kelly, because it sure seemed that the study was saying 180 opposite of what you were saying. Whew.
4. Jen Robinson says:

   March 18, 2015 at 6:46 pm

   Sorry to be dense, but what do OR and RR stand for?

   Is anyone presuming a mechanism, like estrogen or testosterone affecting cancer risk?
5. skeptvet says:

   March 19, 2015 at 7:31 am

   OR is Odds Ratio and RR= Risk Ratio. These are standard measures of the difference in the risk or the odds of an outcome in an epidemiologic study.

   In the case of some cancers, there are known or presumed mechanisms of association between sex hormones and cancer. For example, the effect of estrogen exposure on mammary cancer development is well-established. For most other cancers, the question is still IF there is an association, rather than what the mechanisms of any association might be. It is possible to look for mechanisms without definitive evidence that an association actually exists, but that is a less common way to go about such research.
6. Jen Robinson says:

   March 23, 2015 at 6:06 am

   Thanks for the answer. Not what I hoped for. Ratio based indices are so hard to interpret. Am I right in thinking an RR of 2 means treatment doubles risk over control? But what is the risk of the control? If the risk goes from 1:10,000 to 2:10,000, it doesn’t worry me much. If it goes from 1:10 to 2:10 it becomes serious. I gather the mammary tumor problem is on the order of 2:10 over an intact bitch’s lifetime . . . but I’d guess the risks are lower for male cancers.

   Also, the high CI’s in your tables tend to the high side . . . some are extremely high. They suggest small sample sizes and high variances. Virtually all statistical analyses assume an unbiased sample . . . and it’s absurdly difficult to find sample that represents all dogs.

   Once again . . . .lots of room for skepticism.
7. skeptvet says:

   March 23, 2015 at 9:57 am

   Absolutely. Relative risk can be misleading when the absolute risk is low, which is something I tried to address in my own review of the literature concerning neutering and health. When relative risk is very different and absolute risk is high, as in the case of the risk of pyometra in neutered and intact dogs, then it is fair to conclude a clear effect (a benefit, in this case). When relative risk is fairly high but absolute risk is low, as in many of the cancers studied, it becomes harder to determine whether the specific risk factor should have a meaningful influence on the overall risk assessment and the decision to neuter or not and when. This is further influenced by breed, since risk varies with breed. In breeds predisposed to certain cancers, it may make more sense to delay neutering or not neuter if neutering significantly affects the relative risk of those cancers since the absolute risk is higher, whereas the situation may be different in breeds at lower absolute risk even if the relative risk difference is the same.

   As you say, no simple answers. But given the unthinking, automatic recommendations most vets have made for decades, the very fact that we are more widely acknowledging that there is real uncertainty is an indication that we may be taking a more evidence-based approach, even if that means less clarity in our recommendations.
8. Axolotl says:

   April 28, 2015 at 10:14 am

   I would like to see greater awareness in vets of alternatives to spaying and neutering that remove fertility but preserve the gonads and the normal function of the animals’ endocrine system, such as a vasectomy for a dog or a hysterectomy with retention of ovaries for a bitch (which, if done correctly, eliminates the risk of pyometra).
9. skeptvet says:

   April 28, 2015 at 3:12 pm

   Certainly, research into the pros and cons of such procedures is needed. You seem to be assuming that overall these would be better than gonadectomy in terms of health, and if so I would point out that this is not proven yet, merely a hypothesis, but certainly studying the long-term effects of such procedures would be useful information.
10. WeatherBoy says:

    October 18, 2015 at 4:37 pm

    Evolution is also “merely” a theory, but that doesn’t make it incorrect. I fail to understand how the majority of vets and pet owners, within the span of a few decades, have arrived at the default conclusion–based on minimal evidence–that removing a major part of an animal’s endocrine system is in the best interests of it’s health, at least until an overwhelming amount of new evidence to the contrary comes along. Intuitively, this seems suspicious, so it’s great to see some researchers willing to investigate this issue recently.

    I’m fairly certain that amputating a dog’s legs will be 100% effective against all forms of leg cancer as well as roaming, leg lifting, humping, aggression, jumping up, digging, foot chewing, running away, scratching, and other unwanted behaviors, so it therefore seems logical to recommend every responsible pet owner have their dog’s legs amputated as soon as possible.

    Aside from the myriad biological variables at play, the political, public policy, and profit-driven factors in the neutering debate are powerful and contentious, so it is a very tricky question to investigate objectively. I’d be curious to know why the neutered dogs in the study cited above were neutered, since in Scandinavia and most of Europe that isn’t normally done unless for specific medical reasons, and how the study controlled for that.