What Causes Cancer in Dogs? : Why Do Dogs Get Cancer and How to Avoid It

What causes cancer in dogs and why do dogs get cancer? How do dogs get cancer in the first place?  And what should we be telling our owners, so that they can prevent cancer in the puppies that we sell to them.

Unfortunately, cancer is on the rise in our dogs. About 30 years ago, only about 1 in 10 dogs was diagnosed with cancer.  These days it’s more like 2 out of 3!  And they don’t even drink or smoke…

So, cancer in dogs is definitely on the rise, as it is in humans.  And that’s no surprise.  Because what causes cancer in dogs can also cause cancer in people too, and both are exposed to similar cancer causing agents.

Here are some tips proven to help prevent cancer from happening in our pets:

1 What Causes Cancer in Dogs: Obesity

So Keep your Dogs Lean and Fit

One reason why do dogs get cancer more these days is because they are obese and unfit.  Fit dogs are less likely to get cancer, than obese, sedentary dogs.  Suggesting to our owners that they actually don’t let their dogs get too fat is a good thing.  It helps prevent diabetes and other diseases as well.

And interesting enough, dogs that are allowed to run flat-out at least once a week are at significantly reduced risk of cancer.  So, whether that be at the beach or in the forest or whatever, letting them off the lead and have a flat-out run is really, really good for our dogs.

2. What Causes Cancer in Dogs:  Early Sterilization

So Sterilize Dogs Late

Why do dogs get cancer more if they are sterilized young?  This is why we shouldn’t spay or neuter them too young.  For male and female dogs, sterilization before the age of 12 months messes up their immune system function. The presence of natural sex hormones generated by their own bodies helps the immune system to develop and mature.

And we now know that delaying sterilization till at least 12 months in both males and females helps prevent immune function issues.  This includes related diseases such as autoimmune conditions and cancer.

3. What Causes Cancer in Dogs: Overuse of Routine Medications

So Use Routine Dog Medications Sparinglywhy-do-dogs-get-cancer

Don’t overdo routine veterinary treatments. If we’re using all of the prescribed routine veterinary medications, we think we’re doing the best job for our pets.  But unfortunately a lot of them are associated with an increased risk of cancer.

For example, Permethrin, which is a pesticide that’s found in a lot of flea and tick treatments has been associated with cancer of the liver and lungs in pets. And so can other drugs such as the insecticide Fipronil used in Frontline, which has also been proven to cause cancer in pets.

Rather than use routine monthly treatments, I recommend to only treat for fleas if fleas are actually present on your dog. If you get in early, alternatives such as diatomaceous earth on the dog and its immediate environment can be effective.

For heartworm control, rather than a yearly injection or monthly treatment, I recommend owners only use a heartworm specific medication every 3 months, such as Nuheart.

Nuking intestinal parasites can also harm our pets.  Surprisingly the presence of some intestinal parasites has been shown to be associated with better immune function in laboratory animals and in humans.  So I can’t help thinking, even though there’s no studies to prove it yet, that the presence of some intestinal parasites is likely to be good for our dog’s immune systems too. I wish I had some empirical studies I could actually tell you about but there isn’t anything there at the moment.

What I suggest to my owners is don’t overdo treatments for intestinal parasites. As breeders we have a duty to worm our pregnant and nursing moms and their babies to prevent them being a public health risk to small children.

But, as far as adult dogs go, it’s actually okay for them to have a few worms.  Prevention is best.  Instead of allowing your backyard to become heavily contaminated with intestinal parasite larvae, simply remove all dog poo at least once a week. That will stop the larvae from being able to get out of the poo and into your dog’s environment.

4. What Causes Cancer in Dogs: Environmental Toxins

Avoid Known Toxins in your Dog’s Environmentwhat-causes-cancer-in-dogs

Talking about environment brings us to the next thing that can help prevent cancer in dogs.  That is to minimize the use of toxic chemicals in the home: things like off gassing from new furnishings and carpets, particularly synthetics.  There can be a lot of synthetics in our homes.  They originate from petrochemicals and can give off synthetic estrogens that disrupt hormonal balance and predispose to cancer.

If you’re going to do refurnishing uou’re better off using natural fibers, such as natural timbers, wool, cotton or hemp.

That same goes for cleaning in the home.  It’s better to use natural, non-toxic cleaners for example, vinegar and bicarbonate of soda.

That also goes for the environment where we exercise our dogs.   Carcinogenic chemicals such as 2,4-D, and glyphosate are commonly used in public parks to control weeds.    Exposure to those has been linked with a 70% increase in cancers, notably lymphoma.  So, it’s advisable to minimise our dog’s exposure to those sort of places as well.

It’s very tempting to see a beautiful green park that’s absolutely perfect, with not a weed in sight.  But the only reason it’s perfect is because it’s covered in chemicals.  Our dogs don’t have shoes or clothes on to protect them when they play in those parks. And they end up absorbing the chemicals through their skin. So we should warn our owners to avoid that kind of situation.

5. What Causes Cancer in Dogs: Carcinogens in Food

Avoid Carcinogens in Dog Food

Another risk to our dogs is what we are feeding them.

I’ve always been a proponent for natural feeding.  And one of the reasons is because of the plastics that are associated with a lot of commercial foods.

Even the lining of commercial dog food bags can have plastic, and that can seep into the food.  So, if you’re going to buy a big bag of dog food then see if you can get the ones with the foil lining rather than the plastic lining.

And would you believe a lot of commercial foods even contain plastic? How does it get there? Well, when a large butcher or supermarket has leftover meat that didn’t sell by the used by date, what do they do with it? They just off sell it to a pet food manufacturer.  And it just goes straight into the mix. They don’t bother to unwrap every parcel. They just put it in, plastic wrappers, foam and all, and that plastic and foam mimic estrogen in the body causing hormonal imbalance.

Endocrine disruptors not only can mess up your breeding program, but they can also predispose dogs to cancer.

I hope that you found those tips useful things to tell your owners. We want them to enjoy a long happy time with our dogsr and not have them die too young from things like cancer.

Return from What Causes Cancer in Dogs to Home Page


  1. Roger said:

    Thank you for the interesting article Dr. Howe, I live in the Ozarks, which is a hilly area in the central part of America. We have a lot of ticks and when I say a lot, I mean a lot. I treat for ticks every month except a couple of months in the winter when it is freezing hard. What would you recommend for tick treatment and are their the same risks with tick medicines.

    April 13, 2022
    • Dr. Meg Howe said:

      Hi Roger. Yeah, it’s not easy to do without the harmful chemicals. Recommend keeping your dog’s coat short during tick season. Check and remove any ticks daily. There are some natural repellents purported to help. I haven’t tried them so I cannot verify. Here is a link for more info: https://animalwellnessmagazine.com/natural-tick-repellents-dogs/
      Cheers, Meg

      April 15, 2022

Leave a Reply

Your email address will not be published. Required fields are marked *