Why Do Big Dogs Get Cancer More Often Than Small Dogs

Unfortunately, larger dogs do have higher rates of cancer versus smaller dogs, although all dogs can get cancer.

Why do big dogs get cancer?

It is believed that bigger dogs get cancer at a higher rate than smaller dogs due to a hormone called IGF1. This hormone occurs at higher levels in big dogs and it is linked to an increased risk of cancer.

There may be other reasons as well, but it isn’t entirely clear why cancer is more common in big dogs.

Cancer risk can also be genetic. If you have a purebred or designer-breed dog (like a Labradoodle), make sure you ask if there is any cancer history in its family bloodline. Avoiding cancer in the family history can help to reduce your dog’s risk of cancer.

What types of cancer are common in dogs?

The types of cancer that dogs get are similar to cancer that humans get. Here are the common types of cancer in dogs:

  • Mast Cell Tumors
  • Melanoma
  • Lymphoma
  • Osteosarcoma
  • Hemangiosarcoma

What breeds tend to get which type of cancer?

While any dog can get cancer, certain large breeds are more likely to get certain types of cancer.


  • All breeds

Mast cell tumors


Osteosarcoma (bone cancer)


What is the main cause of cancer in dogs?

Some cancers are genetic, but most cancers in dogs occur from gene mutations that happen because of the environment. Cancers can also be caused by exposure to hormones in the dog’s body from things such as tobacco smoke, pollution, and sunlight.

Other causes of cancer in dogs include:

  • Nutrition
  • Viruses
  • Pesticides
  • Uv light
  • Asbestos
  • Waste incinerators
  • Polluted sites
  • Radioactive waste
  • Canned foods

Unspayed dogs also have a higher chance of developing mammary cancer.

What are the early signs of cancer in dogs?

Cancer is out of control growth of cells in the dog’s body. This can spread into the normal tissues of the body and cause destruction. There are lots of cancer types that can be found in dogs, so regular veterinary checkups are important to catch early signs.

Symptoms of cancer that you may see at home include:

  • Unusual growths in or under the skin. These growths (tumors) can be anywhere on your dog. Make sure you pet your dog regularly as part of their grooming routine.
  • Open wounds or sores that don’t heal like normal.
  • Loss of appetite or loss of weight.
  • Discharge from body openings. This could be bleeding, vomiting, or diarrhea.
  • Unusually bad body odor. If your dog has a tumor or tumors in their anus, mouth, or nose it can cause noxious smells.
  • Decrease in stamina or a lack of interest in exercise or play. This can also happen in old age but is sometimes the first sign of cancer.
  • Stiffness or limping when walking. This might be arthritis, but it can also be an indication of bone, nerve, or muscle cancer.
  • Problems going to the bathroom or breathing. This could be wheezing, straining to poop, or having difficulty urinating.

None of these symptoms mean for sure that your dog has cancer, but they are all a good indication that it’s time to take your dog to the vet to rule out cancer or other problems.

What age do dogs normally get cancer?

Dogs can get cancer at any age. But in studies, the median age of cancer in dogs is 8.8 years.

The recommendation is to start screening for cancer in dogs at the age of 7 years.

How can you prevent cancer in dogs?

While you can’t always avoid cancer in your dog, there are some steps you can take to make it less likely that your dog will get cancer.

  1. Avoid smoking around your dog. Don’t smoke around your dog and don’t let other people smoke around your dog. Secondhand smoke causes cancer in dogs just like it does in children.
  2. Keep your pet at a healthy weight. Obesity can be a risk factor for cancer. Feed your dog healthy food and make sure it gets sufficient exercise.
  3. Know the risk for your breed. Some breeds (see above) are at higher risk for certain types of cancer. If you have a high-risk breed, make sure that you have a thorough medical history for it.
  4. Get regular vet checkups. When you take your dog to a yearly checkup your vet can flag any potential problems, including possibly spotting developing cancer.
  5. Avoid long-term sunlight exposure. Being out in the sunshine is great, but too much sun can increase the risk of skin cancer in dogs.
  6. Avoid asbestos exposure. Asbestos has been linked to cancer in both humans and dogs.
  7. Do a home exam on your pet once a month. Look in the mouth and ears of your dog. Be sure to run your hands along their body and look for anything unusual.
  8. Exercise! Regular exercise will help to keep your pet healthy and reduce the risk of other diseases as well.
  9. Avoid pesticides and herbicides. Lawn chemicals have been linked to cancer in both humans and pets.
  10. Avoid solvents and paints. There is a possible connection between solvents and paints and cancer. Avoid exposure to these, especially when wet.
  11. Know your pet. You are likely to notice behavioral changes in your pet before anyone else does. It’s important that you get to know your pet so that you can recognize if there’s a problem that is arising.
  12. Add veggies. At least one study says that adding veggies to a dog’s diet may decrease its risk of cancer.
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