10 Signs of Cancer in Dogs

Signs of cancer in dogs. Learn the 10 warning signs of dog cancer, what are the canine cancer symptoms, the most common types of dog cancers, and more all in this article!

Illnesses are frightening enough, but there’s something particularly scary about canine cancers. They depend on us for their health, yet can’t tell us when something’s not feeling right. That’s why being on the lookout for signs of cancer in dogs is so important.

It’d be wonderful if this were a rare and minor health issue with dogs, but unfortunately 1 in 3 will suffer from dog cancers in their lifetime according to the National Canine Cancer Foundation.

Now, let’s get into the warnings signs of canine cancer as well as its most common types. Noticing any of these doesn’t necessarily mean your dog has cancer, but there’s a good chance of another health issue at a minimum, so you should contact your vet immediately if any are observed.

Signs of Cancer in Dogs

Notice one or multiple signs in this list? Contact your vet right away.

1. Weird Smells

You’ve probably grown accustomed to your dog’s bad breath, but you should be on the look out for any unusually bad (or just plain different) smells coming from your dog when you’re close enough to smell their breath.

Most times, it will just be due to something easily explainable like a change in diet, but you can never be too careful. Also pay attention for any odd odors coming from the nose or rectal area as potential signs of dog cancer.

2. Pale Gums

Be sure to occasionally check the color of your dog’s gums. Pale gums can be a sign of many health issues with dogs, cancer included. If you notice a change in this area, contact your veterinarian right away.

Here’s how to check your dog’s gums:

  • lift the jowl so you can get a good look
  • press the gums with the ball of your finger
  • observe the gum’s color where you’ve pressed

In healthy dogs, after pressing on their gums the area should turn white briefly. After about 2 to 3 seconds, the color should return to its normal pink. If not, pay attention for other warning signs and consider talking to your vet.

3. Lack of Energy

Has there been any significant changes in your dog’s energy level? Lethargy is also one of the common signs of cancer in dogs. No one knows your dog’s normal behavior better than you, so this is one your veterinarian may not always catch.

Is your dog spending less time playing? Do they tire quickly? Are they spending a lot more time sleeping or just generally seeming disinterested in their usual activities? Look out for these, and when noticed begin looking for other signs your dog has cancer.

symptoms of dog cancer

4. Vomiting and Diarrhea

Sometimes when your dog is vomiting or has diarrhea it can be due to something gross but normally harmless, like eating poop. Unfortunately, though, it’s also one of the common signs of cancer in dogs.

If you notice your dog having diarrhea or vomiting — especially when accompanied by other warnings signs from this list — consult your veterinarian right away. Even if it’s not dog cancer, there could be another health issue that needs to be addressed.

5. Breathing Trouble

Like with people, there are many different types of dog cancer. And like people, you need to be on the lookout for the warning signs of lung cancer in dogs. Pay attention to your dog as they play and go about their usual life.

Are you noticing differences in their breathing, such as coughing, wheezing, or becoming short of breath much more quickly than normal? Be on the lookout for other warning signs and consider speaking to your veterinarian very soon.

6. Bumps or Lumps

If you’re not already,  you should get into the habit of checking your dog’s skin on a regular basis. About once a month is fine. Check by slowly and gently running your hands over your dog’s body, taking notice of what you feel.

Make note of anything that seems unusual or out of place, and if this isn’t your first time checking you’ll certainly want to investigate anything new. Your dog should enjoy this petting, so don’t be afraid to take your time.

Don’t forget to feel behind their ears and around their face. If your dog does not want to be touched in certain areas, investigate closely. Contact your vet immediately if you notice any bleeding or discharge.

canine cancers

7. Unexpected Weight Loss

If you don’t have your dog on a weight loss regimen, and haven’t been feeding them weight control dog food, then unexpected weight loss is one of the most common signs of dog cancer you should be on the lookout for.

Your dog suddenly losing weight may not be cancer, but if there’s no other obvious explanation there’s a very good chance some type of health issue is the cause and you should get into touch with your veterinarian.

8. Change in Appetite

Have you noticed any changes in your dog’s appetite? Are they eating less or not showing interest in food they normally love? Many health issues for dogs could be the cause here, and cancer is unfortunately among them.

Sometimes it can be just a brief issue of not feeling great, or maybe someone else has been sneaking them food when you weren’t looking. Pay close attention to their eating habits any time you notice a change and talk to your vet right away when problems persist.

9. Change in Behavior

Another sign of cancer in dogs you’ll want to be watching out for are changes in behavior. Is your dog limping, walking, or playing differently than normal? Is your normally quiet dog irritable and barking or snapping even at you?

Dogs, just like people, get annoyed or lethargic when they aren’t feeling well. If your dog begins acting strangely and there’s no obvious reason why, there’s a good chance they’re sick and you should speak to your veterinarian.

10. Wounds or Sores

If you notice any wounds or open sores on your dog that aren’t healing as quickly as you’d normally expect, or are appearing with no obvious explanation, get in touch with your veterinarian as soon as possible.

Unexplained sores or slow healing times can be the sign of something serious — including dog cancer. Don’t hesitate to get in touch with a professional right away who can examine your dog for anything that needs to be addressed.

Types of Dog Cancer

We’ve already covered the signs of canine cancers, now let’s quickly cover the different, most common types of dog cancer.


This type of dog cancer is found in the lymph nodes or bone marrow and usually diagnosed in dogs between 6 to 9 years old. It attacks the dog’s immune system and will spread rapidly if not addressed.

There are five stages of lymphoma in dogs, with each having their own treatment options and prognosis. Dog lymphoma is usually first noticed in a painless but swollen lymph node behind your dog’s neck or knees.


A malignant cancer of the blood vessels, hemanglosarcoma is more commonly found in dogs than any other species. It is most often found in the spleen, liver, and heart but can spread to any organ or occur just below the skin.

Unfortunately, there are no obvious early warning signs with hemanglosarcoma and oftentimes it is not found until it is in its advanced stages. This type of canine cancer is most frequently found in large breeds like German Shepherds or golden retrievers.


A type of skin cancer that you’ve likely heard about due to its frequency in humans, melanoma is most often found in or around a dog’s mouth or lips. It can also be found in their nail beds, foot pads, and eyes.

Melanoma in dogs can be particularly aggressive, spreading from the skin deep into a dog’s organs. Early signs of melanoma in dogs include swollen paws, a draining eye, or sores in or around their mouth.

Mast Cell Tumors

Found in the skin and other tissues like the respiratory tract or intestines, mast cell tumors attack a dog’s immune system by turning normally protective enzymes and histamines against the dog.

Mast cell tumors are very common in older dogs. Mixed breeds should be particularly on the lookout as well as boxers, Boston terriers, beagles, and schnauzers. The earliest sign is usually skin lesions, with agitation caused by discomfort also common.


A cancer of the bone, about 85% of osteosarcoma tumors are malignant and will grow very quickly. It is most commonly found in large breed dogs that are 4 to 7 years in age.

Early signs include swelling and lameness. Breeds most at risk include Great Danes, Irish setters, Doberman pinschers, Rottweilers, German Shepherds, and golden retrievers.

Mammary Cancer

Mammary cancer is most often found in female dogs that were not spayed, or were not spayed until after they were 2 years old. Roughly 50% of mammary tumors in dogs are malignant and have metastasized (spread) by the time of surgical removal.

It is tough to spot, with mammary tumors usually appearing only as a small nodule on or around the dog’s nipple.

Please be sure to pay attention to these signs of cancer in dogs. If you notice any one, or multiple signs, then you should contact your veterinarian immediately. Cure rates have never been better, and improve even more with early detection.

Best wishes to you and your pup, and please be sure to pin or share this so you can help other dog parents to know the warning signs of canine cancer!

signs of canine cancer