Chemotherapy in Companion Animals

General Considerations

Determining the best option for your pet with cancer can be very difficult. Reliable information can be obtained from numerous sources including your veterinarian, web resources and cancer treatment specialists.

Chemotherapy (anticancer drugs) is frequently used to control some types of cancer in pets and can be employed alone or in addition to other types of treatments such as surgery or radiation therapy. It may be given orally (pills), intravenously or directly into the tumor.

It is recommended that, when feasible, no other medication be used simultaneously with chemotherapy since it may interfere with the action of the chemotherapy. This is also true for some vitamins and supplements. Please consult your veterinary oncologist for advice about current medications for your pet while on chemotherapy.

What are the benefits of chemotherapy?

Chemotherapy is used by veterinarians at LSU to treat cancers in four basic but different ways

  1. Chemotherapy is the most effective single treatment for some types of cancer, offering the best opportunity for remission while at the same time preserving a good quality of life. A good example of this type of cancer is lymphoma. 
  2. Chemotherapy is often recommended after surgical removal of a malignant cancer. The purpose of chemotherapy in this setting is not only to prevent or delay recurrence of the cancer at the original site, but also to prevent or delay the spread (or metastasis) of the cancer. Examples of cancers for which chemotherapy is routinely used in this way are mass cell tumors, cancers in the spleen and malignant bone tumors in dogs. 
  3. Chemotherapy may be administered to some animals while they are also receiving radiation therapy for the treatment of their cancer. Some chemotherapy drugs are effective in this situation because they increase the ability of radiation to kill the cancer cells.
  4. Occasionally chemotherapy will be used alone for the treatment of cancers that are not amenable to surgical removal or radiation therapy, or have already metastasized. In most of these cases, the goal of treatment will not be to cure the cancer, but rather to improve the patient's quality of life.

How long will my pet receive chemotherapy?

The length of the particular course of chemotherapy will vary depending on the disease being treated. The most common cancer treated with chemotherapy at LSU is lymphoma. Although chemotherapy for this disease is often very successful, owners of cats and dogs with this type of cancer should realistically expect that their pets may need some sort of chemotherapy long-term. The course of treatment for other types of cancer is usually much shorter, with protocols varying from once a week to once a month. The specific length of your pet's individual course of treatment will be discussed in detail with you.

Is chemotherapy expensive?

Treatment of cancer with chemotherapy can be costly. It involves the use of the same drugs used to treat human cancer patients, and many of these are expensive. The cost of chemotherapy is highly variable depending on the drug and protocol chosen by you and your oncologist. In addition, your pet will benefit from the expertise of several highly trained health care professionals. The exact cost of chemotherapy varies with the size of the animals, and the drugs being administered. The projected cost of your pet's individual treatment will be discussed in detail with you as typically there are many options available. 

How is chemotherapy given?

The large majority of chemotherapy drugs used at LSU are given by intravenous injections. At LSU, day admission to the hospital as an outpatient is required. A blood sample is drawn first, and the white blood cell count, red blood cell count, and platelet count are checked to be certain that it is safe to proceed with treatment. The drug itself is then administered through an intravenous catheter. Owners should expect the process to take several hours. 

What happens if I have an emergency? 

Dogs and cats experiencing potentially serious side effects from chemotherapy may be weak and lethargic, may refuse food, may have vomiting and/or diarrhea, may have fevers, or may seem disoriented. If you think you have an emergency and your regular veterinarian has been administering some of your pet's chemotherapy, we recommend that you contact that doctor directly for further instructions. If your pet's chemotherapy treatments are only being given at LSU and you feel you have an emergency, you should contact us at 225-578-9600 (day and evening). In order to ensure proper processing of your call, be sure to identify yourself specifically as an oncology client whose pet is currently receiving chemotherapy. If you are concerned, it's always best to bring your pet to a hospital for evaluation.

What happens after treatment is over? 

It is important for your veterinary oncologist and/or regular veterinarian to examine your pet periodically after chemotherapy is over, usually at 1 to 3 month intervals. This will allow potential problems, such as recurrence or spread of the cancer to be detected before it becomes too advanced. Treatment options will be more numerous and have a greater potential for success when problems are identified early.

Finally, it is important for the owners of dogs and cats receiving chemotherapy to realize that the cancers we treat are rarely cured. Almost all of our patients ultimately have recurrence of their cancers, and their owners will eventually have to make the difficult decision to euthanize their pets. However, it is vital to understand that most cats and dogs receiving chemotherapy have an excellent quality of life both during and after treatment. It is often possible to provide many additional months, or sometimes even years, of happy life with chemotherapy. The vast majority of owners tell us that they have no regrets about their decisions to pursue chemotherapy for their pet.

Side effects of chemotherapy in companion animals

Dogs and cats generally tolerate chemotherapy much better than human patients do. The two side effects encountered most commonly in canine and feline patients receiving chemotherapy are toxicity to the gastrointestinal tract and toxicity to the bone marrow. Normal cells in both of these areas divide very rapidly, so are more susceptible to the toxic effects of chemotherapy.  

When the cells lining the gastrointestinal tract are affected, the result may be loss of appetite, vomiting or diarrhea. The symptoms are usually mild and can be overcome with supportive care at home, rarely requiring hospitalization.

When the cells of the bone marrow are affected, the result may be more serious. The precursor cells that produce the white blood cells necessary to fight infection are found here. If these cells are damaged, the patient's white blood cell count may drop low enough to result in an increased susceptibility to infection. Even bacteria, which are normally not problematic, can cause serious illness in this situation. White blood cell counts of all canine and feline chemotherapy patients are monitored carefully, but uncommonly a cat or dog receiving chemotherapy may develop a life-threatening systemic infection. The only way to successfully treat these infections is to admit the patient to the hospital and administer intravenous fluids and antibiotics. 

Some chemotherapy drugs can be extremely irritating to the surrounding tissue if they leak outside the vein during injection. Examples include vincristine, adriamycin, and mustargen, and severe inflammation, ulceration, and swelling near the injection site can occasionally be seen. This complication occurs rarely, because all chemotherapy drugs are carefully administered through intravenous catheters.

Hair loss in cats and dogs receiving chemotherapy is usually very minor, with some notable breed exceptions. If you own a poodle, West Highland white terrier, Old English sheepdog, schnauzer, puli, Lhasa Apso, Shih Tzu, Bichon Frise, Yorkshire terrier, Maltese, or curly coated terrier such as an Airedale or Welsh terrier, you should expect that your pet will lose hair during the initial stages of chemotherapy. The hair often grows back after your dog's course of chemotherapy has been completed, or once treatments are being administered less frequently. Cats usually do not lose any hair, although they will lose their whiskers. 

Handling chemotherapy at home

Exposure to chemotherapy should be minimized for everyone working with these compounds. Some individuals may experience skin irritation if they come in direct contact with chemotherapy drugs. These drugs may be also absorbed through the skin or mucous membranes or inhaled.

Should I avoid contact with my pet after chemotherapy administration?

Chemotherapy drugs are rarely excreted through your pet's skin; therefore it is not necessary that pets be isolated after treatment. It is always wise to practice good hygiene, such as washing your hands after playing with or cleaning up after your pet and not allowing your pet to lick you on the face.

If you are pregnant, trying to become pregnant, or breast feeding or are immuno-compromised

You should avoid contact with chemotherapy drugs. You should also avoid contact with your pet's waste for 24-72 hours (depending on the drug) after their last treatment with chemotherapy. Contact your physician or veterinarian if you are concerned about your risk of exposure.

Handling the medications

If you are administering chemotherapy at home, you should take special precautions. This medicine requires special storage, handling and disposal. Please keep the medicine in the vial, in which it was provided to you. The medicine bottles should not be stored in the kitchen, near food or cosmetics, and should be kept safely out of the reach of children and pets.

Refrain from smoking, applying makeup, adjusting contact lenses, eating and chewing gum while handling chemotherapy drugs. Do not crush or break the pills. You should wear unpowdered latex gloves (not vinyl) when handling the medicine. Wash your hands thoroughly after contact with the drugs. Dispose of gloves and any empty vials immediately.

Cleaning up after you pet

It is normal for some of the medication that your pet is taking to end up in their urine and feces.  Although the great majority of the chemotherapy drug is already metabolized, trace amounts of active chemotherapy drugs may be present in your pet's urine or feces for 24-72 hours post treatment. It is a good idea to walk your dog away from high traffic areas. If your pet urinates in the house, wear gloves to clean the area. Use disposable paper towels, and rinse the area with a 1:10 dilution of bleach or warm soapy water after the waste is picked up. It is better to pour the cleaner rather than spray it, because of aerolization. For cats, scoop the litter box every 12 hours after chemotherapy administration, and change all of the litter 48-72 hours after chemotherapy. Dispose of all waste appropriately. Any contaminated bedding should be washed in the laundry. It is ideal to wash this laundry once by itself and then wash it again (the second wash can include other laundry). If you have any questions or concerns regarding waste clean-up or disposal, please contact a veterinary oncologist at LSU. 

If you should come in contact with chemotherapy drugs

If an accidental spill or exposure occurs, wash the area thoroughly with soap and water. Contact your physician if you have concerns about exposure to chemotherapy drugs.