Signs of Cancer in Dogs: How Do You Know If Your Dog Has a Tumor?

Signs of Cancer in Dogs: How Do You Know If Your Dog Has a Tumor?

The signs and consequences of cancer in humans are well recognized, but you may not have heard as much about how it could affect your beloved pooch. In fact, cancer is the most common cause of death in domesticated dogs, yet it may go undetected for a long time, drastically reducing their chances of survival.

This article contains the information you need to know the signs and types of cancer that could affect your pet. This is a guide to understanding canine cancer and tips on what to do in case your pet develops the illness.

Key Takeaways

  • Prevention: Many environmental factors may cause cancer, such as exposure to chemicals and some viruses. The chance of disease also increases with age, and long-term obesity contributes.
  • Breeds matter: Professionals have noted that there is genetic predisposition to some types of cancer based on the breed, particularly Golden Retrievers.
  • Listen to your pet: They cannot talk, but tell-tale behaviors show you if they are in pain or discomfort.
  • Early detection is key: If you notice any symptoms, take your dog for a check-up.

When a Dog Has Cancer, What Are the Signs?

The following are warning signs of cancer in dogs and might help with early detection and a veterinary diagnosis:

  • Unusual lumps and bumps: Mast cell tumors commonly appear as masses underneath the skin.
  • Sores that don’t heal: Even with the use of antibiotics.
  • Lameness and stiffness: This can be symptomatic of arthritis in older canines, but prolonged lameness coupled with lethargy is also an indication of cancer in the bones.
  • Increased respiratory rate: Breathing problems and coughing can signal cancer in the lung or a tumor between the ribs.
  • Diarrhea, vomiting, loss of appetite, and weight loss: Digestive problems and weight loss may be a manifestation of cancers in the stomach, digestive tract, or liver.
  • Difficulty urinating: If your pet is suffering from a tumor in their urinary tract, it will be difficult and painful for them to urinate. Look out for traces of bleeding in the urine too.
  • Foul-smelling breath: Bad oral health in canines can be caused by mouth tumors.
  • Swollen lymph nodes: Lymphoma, a type of cancer that affects white blood cells, is common. But swollen lymph nodes mean infection, other cancers, and illness. Lethargy and fever are also signs of lymphoma.

Symptoms of Cancer in Dogs: 8 Common Cancers

Skin Cancer 

Short-haired pets with pink skin commonly develop melanoma or discoloration, which is often harmless (benign). However, canines are susceptible to mast cell tumors that require surgery. Mast cells appear as raised lumps that change in size or shape. If there is a colored lump on your pet, have them examined as it may suggest skin cancer in dogs.

Bone Cancer

Bone cancer in dogs or Osteosarcoma is among the most common types of cancer found in canines [1]. Scottish Deerhounds are genetically predisposed to this disease. It occurs more frequently in larger dogs and older dogs. Golden Retrievers and Rottweilers are also at greater risk. CBD oil can be used to relieve pain and inhibit the growth of harmful cells [2].

Lung Cancer

Thankfully, lung cancer in dogs is relatively rare as it is a highly aggressive type with a low survival rate [3]. Pets may experience pain, fever, lethargy, and coughing. All breeds can develop the sickness, but it more often affects Boxers.

Liver Cancer

Hemangiosarcoma is malignant and spreads quickly to lymph nodes or other vital organs. Liver cancer in dogs usually comes in this form [4].

It causes vomiting with blood, diarrhea, and lethargy. If left to develop, it can also cause jaundice, excessive thirst, and fever. Dogs most susceptible are Golden Retrievers, German Shepherds, Poodles, and Rottweilers.

Spleen Cancer

Similar to liver cancers, spleen cancer in dogs is usually a form of hemangiosarcoma and often affects the same breeds. The effects escalate quickly and typically include body weakness that causes collapse, and rapid heart rate, caused by internal bleeding. Symptoms like this are a medical emergency.

Breast Cancer

Breast cancer commonly affects the health of female dogs and accounts for up to 70% of all dog cancer diagnoses [5]. It usually shows itself as a lump on the mammary. Poodles, Dachshunds, and Spaniels are the breeds most affected by breast cancer in dogs.

Bladder Cancer

Indications of bladder cancer in dogs are usually difficulty urinating and bloody urine. Urinary tract tumors can also cause more general discomfort, such as pain in the abdomen, nausea, and vomiting. If your dog cannot pass urine for more than 24 hours, they should be taken to the veterinary clinic straight away.

Stomach Cancer

Dogs with stomach cancers usually feel it gradually, starting with general nausea and lack of energy. Vomiting and black stools are clearer indications of malignant stomach cancer in dogs that may spread.

Out of 16 dogs, all experienced vomiting, six dogs got anorexia, and five experienced weight loss

Cancer Treatment for Dogs

Chemotherapy, Radiotherapy, or Surgery

Surgery to remove tumor(s) is the most effective solution for pets. However, if the disease has already progressed to a more advanced stage or spread, radiation therapy or chemotherapy may be advised.

These interventions have bad side effects that take a long time to heal from. Some animal owners may choose to manage the condition with pain relief to minimize discomfort to the dog.

Medications to Alleviate Symptoms

Pain relief, anti-nausea drugs, and medicines that soothe gastrointestinal sickness are common veterinarian ways of reducing your dog’s discomfort. Nonsteroidal anti-inflammatory drugs are recommended for pain relief in pets, and there are types specifically made for canines.

Aspirin may be given; however, you should ask for veterinary advice about doses and frequency, as pain killers can damage the lining of your dog’s stomach if overused.

Prescription Painkillers

Veterinary options are available and are tailored to dogs. Ask your veterinarian about these if your pet is experiencing discomfort. Ibuprofen and other painkillers from your cabinet are not recommended for animals. If your dog is in severe pain, your vet might recommend a tranquilizer such as tramadol.

CBD for Dogs with Cancer

Alternative remedies are an appealing option for some dog owners. Cannabis oil treatment has been proven to reverse cancer cell growth, reduce inflammation, and relieve pain with very few side effects [6].

CBD treatment showed to increase one-year survival by up to 83% in dogs with glioma


How Do You Know If Your Dog Has Cancer?

It is not possible for your dog to tell you when they are in pain, but there are a few warning signs that your canine will express when they are feeling unwell and need to see a vet:

  • Drooling. Is your dog salivating a lot from the mouth? This can be a symptom of nausea.
  • Decreased activity or weakness. Do they seem to be lethargic or less sociable than usual?
  • Loss of appetite. Especially when coupled with weight loss and weakness.
  • Vocalization, such as whining and growling. They could be trying to tell you something!
  • Urinating or defecating indoors—a sign that your dog’s not feeling themselves.
  • Excessive licking or scratching the body can express discomfort or pain.
  • Abdominal pain. If they are yelping, snapping, or running away when touched, this is a clear sign medical attention is needed and are not healthy.

How Long Can Dogs Live with Cancer?

Your veterinarian will be able to explain what the type of cancer is and the stage it has progressed to. These factors will confirm what treatments are available and, if treatment is no longer an option, how much time your pet has to live.

Dogs treated with Palladia had a slower tumor progression, prolonging their life compared to the placebo

If treatment is no longer an option, you can make a plan on how you will manage your pet’s quality of life to ensure they are comfortable at home.

What Are the Signs of a Dog Dying From Cancer?

Be aware if your dog is suffering and consider euthanasia if they show extreme discomfort. Difficulty breathing, total lethargy, spontaneous moaning, anti-social behavior, or the inability to rest or sleep can mean that the dog is not healthy or managing anymore.


A diagnosis of cancer for your dog is scary, and no animal lover wants to see their pet suffer. Try to remember that when caught early, cancers can be treatable. Regular attention and checks on your dog, particularly as they age, and being in touch with their behaviors when they are sick, are key to ensuring they remain healthy.


  1. Gardner, Heather L, et al. “Dogs as a Model for Cancer.” Annual Review of Animal Biosciences, U.S. National Library of Medicine, 2016,
  2. Davis MP. Cannabinoids for Symptom Management and Cancer Therapy: The Evidence. J Natl Compr Canc Netw. 2016 Jul;14(7):915-22. doi: 10.6004/jnccn.2016.0094. PMID: 27407130.
  3. Moulton, J. E., et al. “Classification of Lung Carcinomas in the Dog and Cat.” Veterinary Pathology, vol. 18, no. 4, 1981, pp. 514, doi:10.1177/030098588101800409.
  4. Lashnits, Erin, et al. “Molecular Prevalence of Bartonella, Babesia, and Hemotropic Mycoplasma Species in Dogs with Hemangiosarcoma from across the United States.” PloS One, Public Library of Science, 10 Jan. 2020,
  5. Merlo DF;Rossi L;Pellegrino C;Ceppi M;Cardellino U;Capurro C;Ratto A;Sambucco PL;Sestito V;Tanara G;Bocchini V; “Cancer Incidence in Pet Dogs: Findings of the Animal Tumor Registry of Genoa, Italy.” Journal of Veterinary Internal Medicine, U.S. National Library of Medicine,
  6. Kis, Brigitta, et al. “Cannabidiol-from Plant to Human Body: A Promising Bioactive Molecule with Multi-Target Effects in Cancer.” International Journal of Molecular Sciences, MDPI, 25 Nov. 2019,