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Cancer in Pets

What is cancer?

Cancer (neoplasia) is a condition, which results from abnormally rapid proliferation of cells when the immune system is no longer capable of controlling it.

This growth results in the appearance of lumps, which may occur in all parts of the body. They impair the functioning of affected organs. As the disease progresses, cancer cells begin to travel to other areas and organs and cause new tumors (metastases) to appear. Cancer is common to pets (cats and dogs) as it is to humans.

What causes cancer?

Because vets clinics do not run a cancer registry for pets like hospitals do for humans, there is less statistical information about which of the known causes of cancer accounts for what percentage.

Some studies suggest that viruses and infections are common risk factors. Just like in humans, papilloma viruses contribute a substantial share of cancer cases in pets. Poor ecology, exposure to a hazardous substance or radiation can also contribute to neoplasia. Some types of cancer can be hereditary.

Types of cancer in pets

Lymphoma directly affects the immune system of both cats and dogs. Tumors hit lymph nodes and eventually upset the functioning of the entire system. In cats, the disease may be caused by a contagious leukemia virus. Since there is no cure for this type of cancer, it is a fatal diagnosis.

Breast cancer affects both cats and dogs. The majority of cases have been observed in older animals. Estimates say that about 50% of mammary neoplasms in dogs and 80% of those in cats are malignant.

Mast cell tumor is a kind of skin cancer, which is more likely to occur in dogs than in cats. However, in some cases, in young cats MCT may affect internal organs. The survival rate among such animals is very low. Usually, tumors appear on the neck and head in cats. Dogs may develop MTC in any region. Because skin tumors are visible, they are easier to reveal and treat than those affecting internal systems and organs. It should be noted that cats are more likely to recover than dogs.

Osteosarcoma (bone cancer) occurs in large breeds of dogs and mostly hits hind limbs near joints. The disease progresses fast and has a strong metastatic potential. The survival rate is low even if the limb has been amputated and the animal has gone through intensive chemotherapy. Bone cancer rarely occurs in cats.

Testicular cancer is more likely to occur in dogs than to cats. It affects males with a history of cryptorchidism – a condition when one or both testicles remain hidden in the lower abdomen and do not appear in the scrotum.

Signs of cancer

It takes a complex examination to diagnose cancer. However, some changes in the appearance and/or behavior can be a good reason for concern. These include sudden weight loss, lack of appetite, unexplained fatigue, swelling of the abdomen that last for several months, lameness, unstopping diarrhea/vomiting, bloody discharges, bad breath, difficulty defecating/urinating, anxiety, etc.


Treatment depends on the severity of case, as well as type, and stage of the disease. In most cases, the following methods are used:

  • Chemotherapy
  • Radiation therapy
  • Immunotherapy
  • Surgery
  • Cryosurgery

Treatment can be successful when cancer is diagnosed at early stages. If you realize it is too late or the observed cancer type has an almost 100% fatality rate (lymphoma), euthanasia can be considered.


The Decision of Euthanizing Your Pet
Private vs. Communal Pet Cremation

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