So Your Pet Has Cancer

Clinical Oncology Service
Veterinary Hospital of the University of Pennsylvania (VHUP)
Last Modified: June 5, 2013

The "cancer problem" that many people think of as a human phenomenon also affects the animals that live among us. Roughly half of U.S. households are home to companion animals. Like people, more and more companion animals (i.e. dogs and cats) are living longer due to better quality of life, preventive medical care, and vaccinations. And longer life means an increased chance of developing cancer. A study in the early 1980s indicated that nearly half of dogs that lived past age 10 were likely to die of cancer. Just as most of us can expect to have a personal experience with cancer, whether it affects our friends, relatives, or even ourselves, many of us are likely to encounter this disease through our pets as well.

While veterinarians have been treating and studying cancer for some time, it was just a decade ago that veterinary oncology was approved as a board-certified discipline under the American College of Veterinary Internal Medicine. In 1994, radiation oncology was approved as a specialty within this field. This was, at least in part, a response to the increasing prevalence of cancer in animals and to pet owners' desire for treatment options besides euthanasia (putting the animal to sleep). The three standard treatments for cancer in humans: surgeryradiation therapy, and chemotherapy, have been adapted successfully to help animals with cancer. While the goal in treating people is to cure the cancer, treatment for animals focuses on alleviating pain and suffering along with extending life, as long as the quality of that life can be preserved. Dr. Lili Duda puts it this way: "We're not willing to undertake an aggressive treatment that might cure half of our patients, if it is very likely that the treatment will make the other half suffer from serious and even fatal complications." Therefore, treatment is typically much less aggressive than in humans, where the usual goal is curing the cancer.

When your pet is diagnosed with cancer, you may be uncertain about the choices presented to you. Dr. Duda recommends a second opinion from a board-certified veterinary oncologist. This may confirm a chosen course of treatment or open up new options for your pet. How do I find a board certified veterinary oncologist, you ask?

The Veterinary Cancer Society has a helpful website, offering resources for pet owners, including a "Find a specialist in your area".

The American College of Veterinary Internal Medicine has a website with a section for pet owners. They are currently adding a resource to find a

As for any diagnosis, in pet or person, educate yourself on the options, costs involved, pros and cons to treating your pet and make an informed decision.  


Your pet has been diagnosed with cancer. Cancer is a disease that is due to the uncontrolled and purposeless growth of cells in the body. The terms cancer, malignancy, and neoplasia are synonyms. Cancer is not a single disease since it can arise from any tissue in the body. Therefore, there are many types of cancer. Some forms of cancer have the ability to spread to other sites in the body which are often far from the original site. This occurs when cancer cells enter the blood or lymph vessels and are then carried to other organs. Cancers with this type of behavior are considered malignant. Oftentimes, it is the spread of a cancer that causes the greatest problems. When a cancer has spread in this fashion, it is said to metastasize. Some cancers lack the ability to metastasize but may cause significant damage due to growth and invasion into local tissues. Tumors that do not metastasize and are not invasive are considered benign. The term, tumor, is a general word for cancer whether is is benign ("good" cancer) or malignant ("bad" cancer). Oncology is the branch of medicine dedicated to the study of cancer and the veterinarians treating your pet are oncologists.

Tumor Evaluation (work-up): Tumor Staging

The first task of your veterinarian is to determine the extent of the tumor. This information is vital for several reasons including determination of your pet's prognosis (i.e., the expected outcome for your pet as a result of the cancer) and formulation of a plan for treatment.

To gather information that can help to determine the extent of the cancer, your clinician will need to evaluate your pet by several methods. These usually include blood tests (e.g., blood count, chemistry profile), urinalysis, radiographs (X-rays), tissue aspirate, and biopsy. Tests which your local veterinarian may have performed might be repeated at a cancer specialty center due to the changing nature of your pet's illness. In addition, as indicated for specific patients, other testing procedures may include: ultrasound, specialized radiologic studies (e.g. nuclear scan, CT/MRI scan, dye contrast studies), bone marrow aspirate, lymph node aspirate, endoscopy (direct examination of the stomach, colon, or bronchi with a specialized scope), and immunologic studies. The collective process of obtaining this information to ascertain extent of the cancer is referred to as tumor staging. It is important to realize that medicine is not an exact science and that despite these staging procedures, small sites of tumor or tumor in organs that are difficult to study may not be detected.

Once the tumor staging has been completed, your veterinarian will be better able to discuss treatment options for your pet. The goal of such therapy will also be discussed. Tumors that have metastasized extensively are usually not curable. Therefore, the objective of therapy for these animals is palliation (i.e., afford relief of symptoms and possibly prolong life without providing a cure). Localized tumors that are not deeply invasive have the best chance to be cured.

Cancer Therapy

There are several types of therapies used to treat cancer in dogs and cats with cancer. These include surgery, chemotherapy, radiation therapy, and immunotherapy. For some tumors, treatment will consist of a single type of therapy, while combination therapy may be recommended for other types of cancer or for animals with more advanced stage of disease. On occasion, due to the rarity or biological behavior of a particular tumor, a precise treatment recommendation may not be known. In an effort to test newer (and hopefully more effective) forms of therapy, you may be asked to enroll your pet in an investigative clinical trial. The purpose of such a trial is to learn more about the specific type of treatment (that may be of value to humans and other pets with cancer) as well as hopefully providing a benefit to your pet. Only pet owners of animals with tumors for which there is no effective treatment or tumors that have not responded to conventional treatment will be offered investigative therapy for their pets, if appropriate investigative treatment is available.

Should you treat your pet?

Treating animals with cancer is not appropriate for every pet or family. It takes a strong commitment on the part of the owner. Therapy requires frequent trips to the veterinary hospital and can be expensive. For some forms of cancer, treatment, once begun, is never stopped during the animal's life (although the frequency of treatments can be decreased). Your veterinarian cannot do it alone since treating pets with cancer is truly a team effort and the pet owner is on the team. It is important for you to present your pet for treatment precisely when requested to do so by your veterinarian since the timing of cancer therapy is critical for obtaining an optimal outcome. In addition, medicines to be given to your pet at home should be administered by you exactly as requested by your oncologist. Any abnormalities or problems you encounter should be reported to your local veterinarian or oncologist promptly. Always feel free to ask questions and communicate with us.

Keep in mind that your veterinarian is as concerned about the quality of your pet's life as you are. The goal of therapy is to keep your pet happy and minimize discomfort. Although some animals may experience transient discomfort from therapy, treatment of most pets with cancer can be accomplished without major distress or detraction from your pet's enjoyment of life. Just because an animal has been diagnosed with cancer does not mean it's life is immediately over. Your commitment to your pet and your veterinarians' dedication to providing state-of-the-art care will work together to keep your pet as happy as possible.


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