Chemotherapy

Cancer is often a difficult disease to control and frequently requires a variety of treatments.  Similar to cancer treatment in people, surgery, radiation therapy and chemotherapy are often used alone or in combination with other treatments to control cancer in pets. Chemotherapy is frequently used to treat cancer that has spread to other parts of the body, to treat cancer that cannot be treated with surgery or radiation therapy alone or when it may enhance the effectiveness of these treatments.

What is the goal of chemotherapy?
The goal of chemotherapy is to control or eliminate the cancer while still providing the highest quality of life to your pet. Chemotherapy drugs sometimes do not cure cancer but rather control the cancer by killing cells and slowing the progression of the disease. 

What is chemotherapy?
Chemotherapy is drug therapy designed to kill or slow the growth of cancers. Many of the drugs used to treat cancer are derived from natural substances such as plants, trees or even bacteria and are often the same drugs used in people.

How is chemotherapy given?
There are different formulations of chemotherapy.  Some drugs must be given intravenously (IV), others may be given under the skin or into a muscle.  In some cases the drug may be injected directly into the tumor itself. Some chemotherapy can be given orally in pill form.

• IV drugs: Such as vincristine or doxorubicin, an intravenous catheter must be placed for safe administration of the drug.  After administration, the catheter is removed and a light bandage is placed.  The “band-aid” can be removed 1-2 hours after the drug is administered.  If your pet licks at the injection site longer than a day or if the site turns red, this may be a sign that some drug went outside the vein. Please contact your dog’s clinician immediately since this may be a serious complication.

• Oral drugs: Oral drugs are administered by you at home.  It is important that your pet receive all medications as prescribed and that the pills are not crushed or split, nor capsules opened.  It is sometimes helpful to coat the pills with butter, peanut butter or cream cheese to cover the bitter taste of the medicine. If you are administering an oral chemotherapeutic drug, you will be given latex gloves to wear while you handle these pills. When you are finished giving the pills, wash your hands to remove any medication residue from your skin.

How should I handle body fluids while my pet is on chemotherapy?
Do not handle feces, urine or vomitus unless absolutely necessary within 24 hours of the chemo administration.  If your pet has an “accident”, wear gloves and clean the area with disposable items (paper towels, baby diapers, etc.) and dispose in the trash. Wash your hands thoroughly when you are finished cleaning. In general, it is recommended that clothing/ bedding which is soiled by feces, urine or vomitus within 24 hours of chemotherapy administration should be washed twice in hot water.

How often is chemotherapy given?
Some drugs are given daily, others weekly and some only every 2-3 weeks. Your time commitment will depend on the chemotherapy drug protocol you choose to treat your pet with.

What is a chemotherapy drug protocol?
The word protocol refers to a set regime of drug(s) given in a specific time frame. This may incorporate one or multiple drugs. 

How long will my pet receive chemotherapy?
Many chemotherapy protocols involve a series of treatments, followed by a period of careful observation. Continuous, indefinite chemotherapy is not the norm. However, in some patients with advanced disease, chemotherapy may be continued as long as it is controlling the cancer.

What happens when chemotherapy no longer controls the cancer?
Cancers can be initially very sensitive to chemotherapy drugs.  Unfortunately, the cancer may return weeks, months or years later. In such cases, the cancer cells have become resistant to the drugs in a similar way bacteria become resistant to antibiotics. When resistance to one drug occurs, we can often use other drugs. However, each time resistance develops it becomes more difficult to find a drug that the cancer will respond to. In some cases, cancer develops resistance to all drugs.  At this point, your pet’s clinician will discuss with you ways to keep your pet comfortable for the remainder of his/her life.

May my pet receive vaccinations while on chemotherapy?
Recent research indicates it is safe to give your pet vaccines while they are receiving chemotherapy, but the response to the vaccine may not be optimal.  We recommend waiting 2 months after chemotherapy to resume a vaccination schedule. 

What sort of side effects may my pet have with chemotherapy?
The highest quality of life for your pet is our goal, but to be effective in controlling a devastating disease like cancer, chemotherapy drugs are very powerful. Fortunately, pets don’t have as many side effects as humans going through chemotherapy do. Hair loss (alopecia), common in humans but rare in dogs. It is seen mainly with breeds that have constantly growing hair (poodle, shih tzu, cocker spaniel, etc.). Cats generally do not lose body hair, but often lose their whiskers.  Chemotherapy will slow the re-growth of hair in all pets receiving chemotherapy so grooming should be adjusted accordingly. Other potential side effects include nausea, vomiting, diarrhea - most of which are easily controlled with medications / diet change and only last for a few days. A common side effect with many chemotherapy treatments is a decrease in the white blood cell count. This could make them more susceptible to contracting infections if the decrease is severe.  At CSU, we routinely check the blood cell counts before every chemotherapy treatment to insure that the white blood cell count is not dangerously low.

Although the above are the most common potential side effects, they occur in less than 30% of the pets receiving chemotherapy. Other side effects are possible, but are often unique to individual drugs (listed below).

Commonly Used Chemotherapy Drugs

Doxorubicin (Adriamycin®) – Administered IV every 2-3 weeks; side effects include those listed above and potential damage to the heart muscle. We recommend performing a heart function exam (echocardiogram) in some dogs before starting this drug. The dose we use is below the known level that causes heart damage and less than 10% of all pets develop heart problems with this drug.

Carboplatin (Paraplatin®) – Administered IV every 3-4 weeks; side effects can include those listed above, but this drug is generally easier on the stomach and intestines.

Cisplatin (Platinol®) – Administered IV every 3 weeks; side effects include those listed above, but most importantly this drug can cause kidney damage. To avoid or minimize damage, blood work before the administration of the drug will alert your clinician if the kidneys are weak. If the kidneys have normal functioning values, your pet will receive IV fluids several hours before and after the administration of the cisplatin to flush the kidneys.

L-Asparaginase (Elspar®) – Administered as an injection directly into the muscle or just under the skin; side effect- acute allergic reaction. After administration of this drug, either you or a hospital staff person will watch the pet for 15-20 minutes to observe for signs of itchy or red skin, hives, difficulty breathing or collapse. If you see any of these signs after the 15-20 min. time period, contact a doctor or nurse in the Oncology Service at CSU or at your local emergency veterinary clinic.

Mitoxantrone (Novantrone®) – Administered IV every 3 weeks; side effects include those listed above.

Vincristine (Oncovin®) – Administered IV every 1-3 weeks; side effects include those listed above.

Vinblastine (Velban®) – Administered IV every 1-3 weeks; side effects include those listed above.

Cyclophosphamide (Cytoxan®) – Administered by mouth daily for 3-5 days or IV every 3 weeks; side effects include low white blood cell counts and bladder irritation. If you notice your pet is straining to urinate or if you see blood in the urine, stop administering the drug and call your pet’s clinician.

Leukeran (Chlorambucil®) – Administered by mouth daily or every 3 weeks; side effects include low white blood cell counts.

Lomustine (CCNU®) – Administered by mouth every 2-3 weeks; side effects include low white blood cell counts and potential liver damage – blood tests will check for liver problems prior to each dose.

Steroids (prednisone, prednisolone) – Administered by mouth daily to every other day; side effects include increased appetite, increased water consumption, increased urination, panting and, rarely, behavior changes. Cats have lower incidence of these side effects.

Piroxicam (Feldene®) – Administered by mouth daily.. This drug can cause ulcers in the stomach or intestine. Notify your pet’s clinician if you observe loss of appetite, vomiting, or dark/tarlike stools, which could be a sign of digested blood from an ulcer.

Melphalan (Alkeran®) – Administered by mouth every day or every 3 weeks; most common side effect is a low white blood cell count.

If you are interested in other current cancer treatment options; please refer  to surgery and radiation therapy. The ACC offers additional information as Client Hanouts that can be obtained on site or via mail if requested.