Many of our female dogs are spayed at a young age. One of the benefits that vets commonly talk about is that early spaying can almost eliminate breast cancer in dogs. We usually call breast cancer mammary cancer in dogs, but we are talking about breast cancer.
We now know that early spaying is also associated with higher risks of other cancers, like osteosarcoma and hemangiosarcoma. On top of this, we see higher rates of thyroid problems and hip dysplasia associated with spaying early in life.
And on the other side, we have the number one cause of canine death: shelter euthanasia. Dogs need homes and we must fight for population control. Spaying helps.
So now we must start to look at the big picture. We need to weigh the pros and cons, balance this information logically, and come to a recommendation based on current facts.
For these reasons, I advocate in my patients spaying at a later date, perhaps between the 3rd and 4th heat. This way we still get pretty good protection against breast cancer and at the same time hopefully evade the other possible complications of spaying so early.
Now, if we look at female dogs who have not been spayed, a large number of these dogs will develop breast cancer.
So here we have the dog, in her natural state, seeming to have cancer being caused by the presence of normal body parts- her ovaries. If she has them, she is at high risk for breast cancer. If we take them away with early spay before the first heat, the odds of breast cancer drop to almost zero.
Does this make any sense? Do a dog’s ovaries cause her breast cancer?
In the past, I was always puzzled by this. And nowhere did I get a good explanation, an answer to this riddle. The answer does not exist at this time in conventional veterinary knowledge.
But now we know about endocrine disrupting chemicals (EDC’s), also called endocrine disruptors.
EDC’s are chemicals that behave like hormones in the body, but they are not hormones. The are part of civilization. They are found in our environment, especially in our water.
These chemicals usually have effects in the body that are like the sex hormones, especially estrogen. Estrogen is mainly made in the ovaries.
It turns out that when pregnant women (and lab animals) are exposed to these chemicals, the babies have higher risks of cancers later in life. Breast cancer is top on this list.
Where do endocrine disruptors come from? They come from normal parts of every day life in modern society. Take plastic, for example. Plastic is everywhere. Plastic water bottles, the lining of cans, plastic containers, food packages, plastic wrap and more.
Plastic contains a chemical called bisphenol A (BPA). BPA is classified as a “xenoestrogen”. “Xeno” means strange or foreign. So a xenoestrogen is a strange or foreign estrogen. This means in is not made in the body like natural estrogen from the ovaries, but it acts like an estrogen.
BPA is found in the urine of 92% of Americans.
There are a host of other endocrine disruptors out there in addition to BPA. Their source is typically stated as industrial chemicals and pesticides. Another source not discussed much is the urine of women using birth control pills or on hormone replacement therapy.
The odd thing about these chemicals is that is seems low doses have the effects, where high doses may not.
So here we have our dogs (and ourselves), drinking water that is capable of acting like estrogen in the body.
What does this mean? Our dogs have natural estrogens from their ovaries. On top of this, our dogs mother’s have been exposed to water-borne xenoestrogens during pregnancy.
If you add the effects of the normal estrogens from the ovaries to the effects of the xenoestrogens during pregnancy, the combination is probably too much.
We spay these dogs before their first heat, and we remove most of the natural estrogens from body, since the ovaries are removed. The effects of the xenoestrogens by themselves are not enough to cause the cancer later in life, and we tip the scales to a breast-cancer free state. Early spay results in almost complete elimination of breast cancer.
But if we don’t do this, the two effect add up to a plague of breast cancer in dogs that have not been spayed.
This is why it looks like being unspayed “causes” breast cancer. In my opinion, it does not. The missing link are the endocrine disruptors.
It is my opinion that the endocrine disruptors are the most likely explanation for what we see in our dogs. As to whether we have “scientific evidence” to back up this idea, the jury is still out.
In 2005, a review paper was published that states that these risks need immediate attention.
For more inside information on real cancer causes, check out The Dog Cancer Survival Guide.
Dr. Demian Dressler is internationally recognized as “the dog cancer vet” because of his innovations in the field of dog cancer management, and the popularity of his blog here at Dog Cancer Blog. The owner of South Shore Veterinary Care, a full-service veterinary hospital in Maui, Hawaii, Dr. Dressler studied Animal Physiology and received a Bachelor of Science degree from the University of California at Davis before earning his Doctorate in Veterinary Medicine from Cornell University. After practicing at Killewald Animal Hospital in Amherst, New York, he returned to his home state, Hawaii, to practice at the East Honolulu Pet Hospital before heading home to Maui to open his own hospital. Dr. Dressler consults both dog lovers and veterinary professionals, and is sought after as a speaker on topics ranging from the links between lifestyle choices and disease, nutrition and cancer, and animal ethics. His television appearances include “Ask the Vet” segments on local news programs. He is the author of The Dog Cancer Survival Guide: Full Spectrum Treatments to Optimize Your Dog’s Life Quality and Longevity. He is a member of the American Veterinary Medical Association, the Hawaii Veterinary Medical Association, the American Association of Avian Veterinarians, the National Animal Supplement Council and CORE (Comparative Orthopedic Research Evaluation). He is also an advisory board member for Pacific Primate Sanctuary.