What Are the Signs of Cancer in Dogs?

Family around dying dog
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Any dog can contract cancer, but it mostly occurs in older dogs, partially because better nutrition and vet care mean dogs are living longer than in the past. Cancer strikes one in every three dogs, according to the National Canine Cancer Foundation. For dogs over 10 years of age, approximately half of the deaths are cancer-related. As in humans, there are many types of cancers that affect dogs and many clinical signs that can be observed.

Cancer is an abnormal growth of cells that are localized in one part of your dog's body or that is aggressive and spreads throughout the body. The causes of cancers are largely unknown, making prevention difficult. Being aware of possible signs of cancer in pets helps provide early detection and care.

Common Cancers in Dogs

Any dog can be susceptible to any form of cancer. That being said, there are certain cancers that are more common than others in dogs. Some of the most frequently diagnosed cancers are:

  • Hemangiosarcoma: This type of cancer is associated with the blood vessels in the spleen and/or liver. Oftentimes this cancer does not become clinically apparent until the cancer in the spleen or liver ruptures. When a hemangiosarcoma ruptures, it begins bleeding into your dog's abdominal cavity. This is something that requires emergency surgery to correct.
  • Lymphoma: One of the most common types of cancers, lymphoma may develop swellings under a dog's jaw, in front of their shoulders, or on the backs of their knees. Of course, just like in people, dogs have lymph nodes have located throughout their body. Depending on the location of the lymph nodes involved, your dog may develop breathing difficulties, gastrointestinal signs, or other symptoms.
  • Mast Cell Tumors: Mast cells are found in connective tissue and contain the biochemicals histamine and heparin. Oftentimes mast cell tumors will appear as hairless, red raised lesions somewhere on you dog's skin. This type of cancer can spread, so surgical excision followed by biopsy to grade the tumor is recommended. Tumors of a higher grade, such as Grade III or Grade IV are more likely to spread.
  • Mammary Gland Carcinoma: This type of cancer is most commonly seen in older, unspayed female dogs. Spaying your dog, especially before their first heat cycle, will dramatically reduce their likelihood of developing this cancer.
  • Osteosarcoma: This is an extremely painful cancer of the long bones. Dogs that develop it will develop a limp. You may also notice behavioral changes such as growling and snapping as they may become more guarded with their painful limb.

Possible Symptoms of Cancer

  • Any new lump or bump
  • Sores that won't heal
  • A change in size, shape or consistency of an existing lump
  • A runny nose, especially if it is bloody
  • Difficulty urinating or bloody urine, which is also common with urinary tract infections
  • Straining to defecate, or thin ribbon-like stools
  • Vomiting or diarrhea, both of which are common with many other diseases
  • Limping or a change in your pet's regular gait
  • Foul breath, excessive drooling or teeth that have moved
  • Drainage and odor from the ears, which is also common with ear infections
  • Increased water intake and urination
  • Lethargy or lack of appetite
  • Weight loss
  • Difficulty swallowing or eating
  • Difficulty breathing

Breed Disposition to Cancer

Cancer is seen more often in some breeds than others. Breeds such as golden retrievers, boxers, Bernese mountain dogs, Great Danes, German Shepherds, Rottweilers, and standard poodles. Hemangiosarcoma is the most commonly seen cancer in golden retrievers, German Shepherds, and Rottweilers. Golden retrievers may also develop osteosarcoma, lymphoma, or mast cell tumors. Rottweilers are also prone to lymphoma and osteosarcoma. Boxers are highly prone to mast cell tumors and lymphoma. Bernese mountain dogs are prone to something called histiocytic malignancies. This type of cancer can effect the dog's spleen, lungs, liver, and even their abdominal lymph nodes. Osteosarcoma is the most commonly diagnosed cancer in Great Danes.

The reason for some breeds being more prone to cancer than others can be environmental but it can also be genetic. While researchers now know what some genes in your dog's DNA code for, they are still trying to understand how the coding controls a dog's susceptibility to cancer. It's important to remember that while there are breeds that are more prone to cancer than others and while certain types of cancer are more common in certain breeds, it's important to remember that any breed can develop any type of cancer.

Cancer Treatment Options

Any time your pet's behavior changes, you should check in with your veterinarian. For cancer as well as other illnesses, early diagnosis and treatment are key to a favorable outcome. Treatment for cancer can involve surgery, chemotherapy, and radiation, but the best option is to catch it early before it spreads.

Not every cancer can be treated successfully. Some owners opt out of aggressive treatment and instead work with their vets to provide pain management.

Nurse preparing operation for an anaesthetized dog in animal hospital
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Is Prevention Possible?

You can't prevent all cancers, but you can take steps to lower the chances your dog will develop it. Healthy nutrition and exercise help. So can having your dog spayed or neutered when it is young. This prevents most reproductive cancers.

Even though prevention of cancer isn't usually possible, when you find out about cancer early, your dog has the best chance for a successful outcome. Be vigilant and proactive to protect your pet.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Dog Cancer Information & Help. The National Canine Cancer Foundation.

  2. Visceral Vascular Tumors. VCA Hospitals.

  3. Lymphoma in Dogs. VCA Hospitals.

  4. Mast Cell Tumors in Dogs. VCA Hospitals.

  5. Malignant Mammary Tumors in Dogs. VCA Hospitals.

  6. Osteosarcoma in Dogs. VCA Hospitals.

  7. Which Dog Breeds are More Prone to Cancer? The National Canine Cancer Foundation.

  8. What Is Cancer? VCA Hospitals.

  9. Cancer Treatment. Merck Veterinary Manual.