Spay/neuter and the association with cancer in dogs: part two
Updated: May 13th, 2019
Spay Neuter Rottweiler: Susan Ettinger, DVM, Dip. ACVIM (Oncology) continues her discussion on how spaying and neutering dogs can increase their risk for certain aggressive cancers.
In part one of my series on spay/neutering, we reviewed the data that sex hormones can promote certain cancers, specifically anal gland tumors in males and breast cancer in females.
But more recently, there is evidence that less exposure to sex hormones increases risk for other aggressive cancers, including osteosarcoma, bladder transitional cell carcinoma, and prostate cancer, lymphoma, and mast cell tumors. So sex hormones may not be all bad, and in fact may be PROTECTIVE again certain cancers.
Osteosarcoma (OSA) is the most common bone cancer in dogs, accounting for about 85% of bone cancer cases. It is very aggressive: 90% of patients will die from the metastasis within the 1st year when amputation is the only treatment. Median survival times for OSA cases with amputation and chemotherapy increase to ten to twelve months, with 20-25% of dogs still alive at two years. I’ve recently written a series on OSA, if you want to read more about them.
Here is the rundown on how spay/neutering seems to influence cancer development:
Purebred dogs who have been spayed or neutered are twice as likely to develop osteosarcoma (bone cancer).
Look in the last section of the book for specific recommendations for each of the most common dog cancers, including osteosarcoma!
The risk is even higher for Rottweilers. One study looked at 683 Rotties and showed that both male and female Rotties who were surgically sterilized before the age of one year had an approximately one in four risk for developing osteosarcoma during their lifetime, while intact Rotties were much less likely to develop the disease. Spayed/neutered Rotties were 4 times more likely to develop OSA.
In a 2002 study, neutered males were 4 times more at risk for prostate cancer than intact males.
Then in 2007, a second study showed castration increases the risk for developing bladder and prostate cancers by three to four times.
The greatest risk was for prostate transitional cell carcinomas (TCC), with an overall risk of 8.
Spaying has also been shown to increase the risk of lymphoma. Intact females had a significantly lower risk, not just lower than for female spayed dogs, but also lower risk for both intact and castrated males.
Interestingly, in people, women also have a lower risk for lymphoma than men.
For all types of heart tumors, the relative risk for a spayed female was greater than 4 times that for intact female dogs.
For cardiac hemangiosarcoma (HSA), female spayed dogs were greater than 5 times the relative risk than for female intact dogs. Castrated males were also at slightly greater risk than that for intact males.
In the next post, I will discuss 2 brand new studies looking at the possible protective effect of sex hormones for cancer. The 1st study looks at the effect of neutering on both joint disorders and cancers in Golden Retrievers.
The 2nd study looked at sterilization, which found sterilization increased how long the dogs lived, EXCEPT sterilized dogs were more likely to die of cancer (and immune-mediated disease).
We will also discuss some recommendations on when to spay or neuter your dog. (Yes, I still think spay/neuter is a good idea, but when for your dog?)
Live longer, live well.
Spay/neuter and the association with cancer in dogs: part one
Spay/neuter and the association with cancer in dogs: part three
Sue Ettinger, DVM. Dip. ACVIM (Oncology). Dr. Sue is a boarded veterinary medical cancer specialist. As a Diplomate of the American College of Veterinary Internal Medicine (Oncology), she is one of approximately 400 board-certified veterinary specialists in medical oncology in North America. She is a book author, radio co-host, and an advocate of early cancer detection and raising cancer awareness. Along with Dr. Demian Dressler, Dr. Sue is the co-author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity.
My female is three years old had two litters of puppies is it too late to spade her?
Hello Cindy, the timing of when to spay your dog should be guided by your veterinarian, of course. But Dr. Dressler generally advises spaying after the third or fourth heat. I spayed my female dog at 10, but it was part of a cancer surgery. Looking back now, I think I would choose to have her spayed earlier in her life, after her third or fourth heat as Dr. Dressler suggests. It’s never “too late” to spay your dog, if you and your veterinarian think it’s the right thing!
Much of what you say just compares spayed dogs to intact dogs. It doesn’t compared early spay to spaying later, which is really what I need to compare. Lymphoma, for example, you say, “Spaying has also been shown to increase the risk of lymphoma. Intact females had a significantly lower risk…” It says nothing about the risk of lymphoma for a dog spayed at 6 months vs one spayed at 1 year. The statement above would imply NEVER spay in order to reduce risk of lymphoma. That’s not practical for most dog owners. I will spay my dog. I am just trying to figure out when. I need more comparisons of spay at 6 months vs. spay at 1 year, or 1.5 years, etc, not spay vs intact. So, while interesting, this article doesn’t really help me decide WHEN to spay.
Hi Crista! There’s no “one right time” that we know of at this point, but in general, early spays are considered problematic in terms of increasing the risk of more aggressive cancers later in life. Dr. Dressler makes a concrete recommendation in this post: https://www.dogcancerblog.com/blog/steps-to-help-avoid-canine-cancer-part-2/ and in his book he recommends, in general, waiting to neuter males until they are 18 months old, and until after at least the first heat for females, ideally even later. Please see The Dog Cancer Survival Guide for more details, and keep in mind that this is a very complex subject. What’s right for you and your dog might not be right for someone else and their dog.
Will a partial spay (leaving ovaries intact) help decrease the chance of certain cancers like being completely intact does?
I want to know why we have to remove the hormone producing organs. Take the uterus, leave the ovaries (like in humans), tie the vas deferens don’t take the testicles (like in humans) It preserves the hormones but takes away reproductive capabilities and that is all we really want.
Wrigs is an eleven year old Wire hair Fox Terrier.. He was in partial remission last week at 3rd CHOPs.This week his nose and node are bigger. They said they are pulling out the big guns with another drug. .He has T cell lymphoma . I pray that we can have him for awhile longer. At first they thought it was B cell lymphoma..
He had one pill of Lomustine last night and has not moved much since. He also received Denamarin.
They are still keeping him on prednisone. Purdue oncologist says no supplements from the beginning . I think our vet would be willing to try. Would a smaller dose of Apocaps be okay? He weighs 32 #.right now he is just laying around. Please help.
I realized I put my question in the wrong section.
My Standard Poodle is 23 months old and I am waiting to spay and have her stomach tacked. She has only had two heat cycles. I am considering lapraroscopic spay and gastroplexy done. Is it best to have her ovaries and uterus removed (ovariohysterectomy) or is it just as safe to leave her uterus (ovariectomy)? Pyometra is a concern. Do you prefer the traditional spay and tacking? The DCSG says to spay between the 3rd to 4th heat for females. I also want to make sure that her bone growth is complete, she is very athletic. I know you said the exact time to spay isn’t known for sure but when would you recommend spaying my girl? I lost my Airedales one to a brain tumor, one to DCM and hemangiosarcoma and one had a pheochromocytoma. They were all spay/neutered early. Nothing is a guarantee but I want to do all that I can. Thanks so much.
Do you have references for the studies you’ve cited? I would be interested to read. Thanks.
Hope these references help:
OSA: Cooley, 2002
prostate: Teske 2002 and Bryan 2007
Lymphoma Vilamil 2009
cardiac: Ware 1999
References for 2 new studies in part 3
All my best, Dr Sue
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