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Are All Tumors Cancerous In Dogs? Health & Care Facts

Does finding a tumor on your dog mean he has cancer? Find out the symptoms of dog tumors, how to determine if they’re cancer and your options for treatment.

Written by: Sassafras Lowrey, MFA, CPDT-KA, CTDI

Last Updated on February 15, 2024 by Dogster Team

A hurt dog with his leg bandaged.

Are All Tumors Cancerous In Dogs? Health & Care Facts

As they age, many dogs get lumps, bumps and masses under their skin. Some of these dog tumors are benign, fatty growths that are completely harmless, but one in four dogs will receive a cancer diagnosis in their lifetime, and cancer is the second leading cause of death in older animals.

To learn more about dog tumors, when pet parents should worry and what treatment looks like if dog tumors are cancerous, we sat down with Dr. Barbara Biller, an Associate Professor of Oncology at the Colorado State University Flint Animal Cancer Center and a member of the American Animal Hospital Association Oncology Task Force, who authored the 2016 Oncology Guidelines for Dogs and Cats.

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Dog tumors, lumps and bumps

A sick dog at the vet.
A sick dog at the vet. Photography ©Chalabala | Thinkstock.

Beyond making sure your dog has regular annual wellness checkups, Dr. Biller mentions looking out for these dog tumor symptoms. If your dog starts to develop skin lumps, or you notice any abnormal swellings or masses growing, bring your pup to the vet ASAP to determine if they are benign (not cancerous) or cancerous growths. Dog tumors aren’t something you can treat at home, so any unusual or new growths should be checked out by professionals.

Diagnosing dog tumors

If your dog has a growth, your vet will likely perform a needle aspirate, which Dr. Biler explains doesn’t involve any need for sedation. “The veterinarian takes a needle and pokes that needle into the mass, drawing back some cells in the mass with the syringe that can be looked at on a microscope,” she explains. Your vet will usually order some blood tests and perform a physical examination.

If your dog’s tumor isn’t cancer

If your vet confirms that your dog’s tumor isn’t cancer, that’s really good news! My 15-year-old Chihuahua mix has a benign tumor on his chest, so I know what a relief it is to hear the doctor say that a growth isn’t cancerous. While my vet said the lump was unlikely to become cancerous, it’s still important to keep an eye on it. We were told to monitor the tumor to make sure that it didn’t rapidly change in size, develop any kind of sore and — because the tumor is near his armpit— that it didn’t impact his movement in any way. Of course, you should still bring him in for regular checkups.

If the dog tumor is cancerous

If your dog’s tumor comes back positive for cancer, your vet will likely recommend surgery, radiation, chemotherapy or a combination of the above.

Veterinary medical advancements have also opened the doors to new and better cancer treatments designed specifically for dogs. “In the last couple of years, there are actually chemotherapy drugs that are designed just for dogs. These are dog-only, chemotherapy-type drugs that are potentially more effective for dogs and are less expensive for owners,” Dr. Biller shares.

The cost of treating cancerous tumors 

Dr. Biller stresses that treating a cancerous tumor isn’t necessarily expensive. The price of treatment will depend on what you and your veterinarian decide is the best approach for your dog’s specific diagnosis. Many veterinarians will work with owners on payment plans, and chemotherapy for dogs can be much cheaper than it is for humans. Dr. Biller estimates that treatment can be as low as $50 a month, or it could range upward of $10,000 for a more complicated course.

Dr. Biller also encourages getting health insurance for your dog while he is young and healthy before lumps and bumps develop. Many canine health insurance plans are now covering diagnostics and treatments for any tumors your dog might develop so long as your pup was on the plan before receiving a diagnosis.

weimaraner dog checked by vet
Image Credit: LightField Studios, Shutterstock

Quality of life when your dog has a cancerous tumor

While cancerous tumor treatment for people and dogs looks very similar, there are some big differences.

Dr. Biller explains that treating dogs is, “very different, in a positive way, from what humans experience,” she says. “One of the big differences is that even though we use the same treatments like chemotherapy, surgery, radiation therapy or combinations, the quality of life during the treatment — not just when [the dogs] are done — is good. Meaning that most dogs and cats handle treatments for cancer really well with a very low chance of severe side effects. Most dogs and cats don’t have any outward side effects.”

Clinical trials for dog cancer

Just like with humans, many veterinary hospitals are working on clinical trials to develop new and hopefully more effective cancer treatments for dogs. The costs associated with treatments in clinical trials are usually fully covered by the research hospitals. Ask your veterinarian to refer you, or learn more about various clinical trials your dog might be eligible for in the US and Canada by visiting

Not happy with the treatment? Get a second opinion

Dr. Biller also encourages dog owners to get second opinions, especially if your veterinarian is telling you that you have an old dog and there is nothing you can do about a growth or tumor. “If someone has told you there is nothing you can do, it may be worth a second opinion,” she says. Dr. Biller encourages dog owners to find another veterinarian, or even to go directly to a specialist. She says that most canine oncology specialists will see new patients without a referral, and even if there isn’t a firm diagnosis. “People can self-refer if they aren’t happy with the message they are getting from their vet.”

Read more about lumps on dogs on

Sassafras Lowrey is an award-winning author. Her novels have been honored by organizations ranging from the Lambda Literary Foundation to the American Library Association. Sassafras is a Certified Trick Dog Trainer, and assists with dog agility classes. Sassafras lives and writes in Brooklyn with her partner, a senior Chihuahua mix, a rescued Shepherd mix and a Newfoundland puppy, along with two bossy cats and a semi-feral kitten. Learn more at

Featured Image Credit: blanscape | Thinkstock.

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