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Cancer in Dogs - The Ultimate Guide

Old smiling dog playing in a park

No one likes to hear the bad news that their pet has been diagnosed with cancer. While this can be a very broad term for many different types of masses that your pet may have. Some may be very aggressive while some are not so scary.

What causes cancer?

There are many causes of cancer. Some are due to genetics while others are environmental. Certain dog breeds such as boxers and golden retrievers are genetically pre-disposed to cancer. Just like in people dogs can develop cancer from second-hand smoking from their owners.

Signs of Cancer

Old grumpy Boston terrier on a sunny day

There are many different signs of cancer in dogs. Some of the symptoms that we see are very vague and some are obvious.


If your dog has a lump, this is an obvious sign that your dog may have cancer. Not all lumps are malignant (cancer) some are benign (not cancer). If you see a lump on your dog, your veterinarian can determine if this lump is cancerous or not.

Sores that won’t heal

Dogs that get a cut or abrasion that just will not heal is a sign that this could be associated with cancer. Sometimes these sores will not heal because the infection present is resistant to the type of antibiotic that they are taking

Loss of appetite

If your pet is not eating this could be a sign of cancer inside the intestinal tract. Some cancers can grow inside the intestines blocking food from passing through. This is not the only reason your dog may not be eating, numerous gastrointestinal diseases can also cause your dog to not want to eat.

Bad Breath/ Foul odors

If you notice your dog has horrible smelling breath, this may be a sign of cancer. Most dogs need dental cleaning every 1 to 3 years. If you notice bad breathing, checking for masses in their mouths and scheduling them a dental cleaning will help make sure everything is okay in their mouths. Though this could be due to other oral issues.

Mouth, Anus or Nose

Dogs can get cancer almost anywhere. Masses can grow in their mouths, around and in their rectum and even in their nose. It is a good idea to give your dog a monthly check over for any new lumps and bumps and get your dog checked out sooner rather than later.

Larger Pug playing in a grassy area

Abnormal Discharge

If your dog has abnormal discharge from the nose, eyes, mouth, or penis/ vulva. This could be a sign of cancer. This could also be an infection.

Weight Loss

A common sign that veterinarians see with a cancer diagnosis is sudden weight loss that was not intentional. Usually, these dogs will have a loss in the muscle around their hips and head.

Changes in Bathroom Habits

Your dog may be going to the bathroom more frequently or having accidents inside the house. If you notice this, they may have a urinary tract infection or have bladder cancer.

Less active

As a dog's age, we expect them to become less active but a sudden decrease in activity level may be a sign of cancer.

Lameness (stiffness or limping)

If you notice your dog limping and a swollen joint, this may be a sign of bone cancer.

Black Stools

Watching your dog’s stool and make sure it is constant every day is best. If you notice black tarry stool this is usually a sign of something serious going on with the intestines such as cancer.

I think my dog has cancer

Yellow lab happily being pet on a beautiful day

If you find a lump or bump on your dog this does not always mean that your pet has cancer. Sometimes these masses are just fatty deposits. If you notice any lumps or bumps get your pet checked out by your veterinarian.

Visit your vet

Your veterinarian can check all your pets’ masses and let you know if they suspect cancer or not. They will take a small biopsy with a needle and look at the cells under the microscope.


Small grey dog looking up with a floppy tongue

If your pet has been diagnosed with cancer there are many different options for helping get rid of your dog’s cancer.

Surgery, chemotherapy, radiation, and immunotherapy or a combination of therapies.

Depending on the location and type of cancer your veterinarian may recommend removing the mass surgically. Some cancers can not be fully removed surgically and chemotherapy or radiation is used to help kill the cancer cells. Many times a combination of surgery and chemotherapy or radiation is used to treat your pet's cancer.

A dog who is undergoing chemotherapy will not have the same side effect as humans. Veterinarians do not use as high of dosages of chemotherapy in pets and human doctors do. Veterinarians goals with chemotherapy are to prolong a good quality of life not make your pet suffer while they are undergoing their chemotherapy treatment.

CBD oil

CBD oil has also shown to help decrease cancer growth. It will also help with the side effects of chemotherapy. CBD is a great additive to give for dogs undergoing chemotherapy, radiation or post-surgery. CBD will aid in decreasing pain, increase appetite and reduce nausea.





Some somethings can be done to help prevent your pet from getting cancer.

Spaying/ neutering

Spaying and neutering your pets young not only eliminates unwanted pets but can prevent mammary, uterine and testicular cancer.


Keeping your pet up to date on vaccines will help prevent common diseases. This will help your pet stay healthy.

Proper Diet

Feeding your pet, a well-balanced diet will help them stay healthy.

Dietary Supplements

As your pet ages giving them extra vitamin and minerals to help boost their immune system.

Pit Bull looking up at the camera with a white background


Many supplements such as CBD oil is a good supplement to give your pet daily to help decrease the chance of your pet getting cancer by reducing bad cell growth.

Environmental Factors

Certain environmental factors such as smoke, air pollution, and pesticides can cause cancer. If a member of your house smokes it is best to be done away from pets.


Pesticides that are used on your yard can be linked to certain types of cancer. Usually, if you let these pesticides sit on your yard for a few hours before allowing your dog outside or using all-natural pesticides will help decrease the chance of cancer.

What you need to know

Small pug sticking up out of tall grass

If you see any lumps or bumps on your dog, it is best to take them to the veterinarian sooner rather than later. As cancer grows it can also spread to other locations in the body. If caught earlier there are many more options with a more successful outcome. 

Cancer is never a good word to hear and many people jump to scary conclusions. Luckily medicine has come a long way and there are things we can do to lessen the severity or discomfort. We hope this has helped you decide your next step for your furry friend to get them on a path to health!

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Dr. Sara Ochoa DVM author at sitstay.com

Dr. Sara Ochoa DVM
Since she was a little girl, she knew that her dream was to become a veterinarian. With a tremendous passion and love for animals that makes her a great source of knowledge for others. She lives happily with her husband Greg and her babies Ruby the Schnoodle, and Bam-Bam the bunny.

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