Cancer in Dogs


What is Cancer?

Cancer, regardless of the species in which it occurs, is the uncontrolled growth of abnormal cells. Cancer cells develop because of damage to DNA. Dogs can inherit damaged DNA, which accounts for some hereditary cancers. More often, though, a dog’s DNA becomes damaged by exposure to something in the environment, such as carcinogens.

Not all tumors are cancerous. Benign (noncancerous) tumors do not spread to other parts of the body and, with very rare exceptions, are not life threatening. Malignant tumors can spread (metastasize) to other parts of the body, where they begin to grow and replace normal tissue. Regardless of where a cancer may spread, however, it is usually named for the place it began.

Cancer is the leading cause of death in dogs over the age of 2 years, and risk increases with age. Some breeds are also more susceptible to certain cancers. Feeding your dog a healthy diet, providing regular exercise and avoiding known carcinogens will help reduce the cancer risk. Spaying or neutering your dog may also reduce the risk for developing certain cancers. If cancer is diagnosed, your veterinarian will discuss the best treatment options for your dog. Treatment success depends on the type and extent of the cancer, as well as the aggressiveness of therapy. Many cancers can be cured, and all patients can be helped to some degree with a proactive plan to provide supportive therapy and pain management.

Some Types of Cancer



Mast Cell



Squamous Cell Carcinoma

dog pain

What are the Side Effects of Chemotherapy in Pets?

The goal of chemotherapy in pets with cancer is to preserve the highest quality of life possible. However, there may be some side effects following treatment with chemotherapy. The overall impact of side effects is reduced by altering doses or eliminating drugs from treatment if side effects are significant. However, in order to obtain any benefit from chemotherapy it is necessary to use doses that can result in some reversible and temporary effects on normal tissues. The most common side effects of chemotherapy in pets include: Stomach upset resulting in a reduced appetite, nausea, vomiting, diarrhea and dehydration. These effects are generally mild and self-limiting but may require symptomatic treatment or hospitalization in some instances.

Supportive Care

Many dogs that have cancer are generally middle aged or older. Age is not a disease but there often other health problems in older pets with cancer that must be managed simultaneously with the cancer. In addition, cancer can produce some problems in other organs such as anemia, kidney problems and digestive abnormalities. The complete management of cancer in dogs requires consideration of supportive measures. These supportive measures can be considered in several categories: nutritional considerations, blood product support and, ancillary medication for concurrent diseases or symptoms.

Pets with cancer require consistent, high quality nutrition. The specific nutritional needs for pets with cancer are not completely understood. The brands of the food are less important than a complete, balanced and palatable food for your pet with cancer.


A poor appetite and weight loss can result from cancer in several ways. Cancer can affect appetite, smell, metabolism and the physical ability to chew or swallow. Treatment for cancer may also reduce appetite by inducing nausea or irritation to the intestinal tract. Numerous means of dealing with nutritional issues in pets with cancer now exist and this aspect of management should be carefully considered with your veterinarian.

For Information about Palliative Care and Cancer, see our follow up article.

See our Breed Guide for more specifics on your pet.