What is chemotherapy? 

Chemotherapy is the use of drugs 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. Most of the chemotherapy drugs used in pets are the same drugs used in people. Similar to cancer treatment in people, chemotherapy can be used alone or in combination with other treatment modalities (e.g., surgery, radiation therapy) to treat cancer in pets. Chemotherapy comes as oral pills/capsules or injectable liquids (such as for injection into the vein or under the skin).  

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What is the goal of chemotherapy? 

The primary goal of chemotherapy is to provide the highest quality of life for your pet while we treat your pet for the cancer. Depending on several factors, including the type and stage of cancer, the intent of chemotherapy is one of the following:  

1. Eliminate cancer: typically used in combination with other modalities to enhance their effectiveness and to treat microscopic disease within the body 

2. Control cancer: used to slow the progression of cancer, such as when it is affecting more than one part of the body  

3. Palliate the signs associated with cancer: used when cancer is not effectively controlled with or amenable to surgery or radiation therapy  

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How does chemotherapy work? 

Chemotherapy is considered a systemic therapy because it circulates throughout the body. Conventional chemotherapy affects rapidly dividing cells, which is characteristic of cancer cells. Non-conventional chemotherapy typically affects the tumor’s microenvironment or targets a specific genetic mutation within the tumor. Depending on the cancer type and stage, more than one chemotherapy drug may be used, either sequentially or simultaneously. Chemotherapy drugs can be given by different routes, including intravenously, subcutaneously (under the skin), orally, into a body cavity (such as into the thoracic cavity), or into the tumor itself. The chemotherapy dosing schedule depends on the specific drug(s) and the cancer being treated.   

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Will Chemotherapy make my pet sick? 

Although veterinary oncologists use many of the same chemotherapeutic agents as human oncologists, the goal is different. In human oncology, the goal is often to cure. Veterinary oncologists choose drugs, dosages, and combinations that minimize side effects while providing the best possible treatment benefit for your pet. We treat cancer as aggressively as we can but not at the expense of the pet’s quality of life.  If your pet starts to experience significant chemotherapy-related side effects, we alter our treatment plan. Fortunately, pets receiving chemotherapy tend not to experience as many side effects as their human counterparts. In fact, many pets experience no side effects.   

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Generally, dogs and cats that receive chemotherapy feel normal on the day they receive the drug. If anything, they may feel slightly more tired that day. Approximately 3 to 5 days later, you might notice that your pet does not feel 100%.  But within 24 to 48 hours, he or she is back to normal until the cycle continues with the next dose of drug.  After each dose of chemotherapy, we discuss whether the side effects observed in his or her pet would warrant a change in therapy.  If everyone agrees that the pet’s quality of life is good and there is evidence that the chemotherapy drug is working against the pet’s cancer, we continue the treatment.   

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However, every pet is different. A small percentage of pets are more sensitive to chemotherapy, and it is impossible to predict which pets will experience more severe chemotherapy toxicity. If severe toxicity occurs, hospitalization for a few days in a veterinary clinic may be necessary. Fortunately, the need to hospitalize pets due to chemotherapy-related side effects is uncommon, and some studies show that hospitalization is necessary in less than 10% of patients receiving chemotherapy. If your pet experiences significant chemotherapy toxicity, we can decrease the dose or change drugs in an attempt to avoid side effects. In addition, at any time, if you are unhappy with the side effects associated with chemotherapy, you can always choose to stop treatment.  Many dogs and cats are able to complete their chemotherapy protocol without experiencing any side effects or only experience mild toxicity. 

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What are the possible side effects from chemotherapy? 

Although side effects are uncommon, the most common side effects from chemotherapy are secondary to the chemotherapy’s impact on the gastrointestinal tract and bone marrow. These side effects typically occur at a predictable time and are generally temporary, resolving within a few days. Pets will recover with time and, if needed, supportive medications.   

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Gastrointestinal side effects: 

Gastrointestinal side effects occur because chemotherapy damages the cells lining the stomach and intestines. These signs are often seen 3-5 days after chemotherapy is administered. Your veterinary oncologist will prescribe anti-nausea and anti-diarrheal medications that you can use at home if you notice any worrisome signs. Some pet owners will preemptively use anti-nausea medications to prevent nausea.  

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At home recommendations:  

• Nausea/Inappetence: If your pet shows signs of nausea (drooling, lip smacking), a picky appetite, or loss of appetite, start an anti-nausea medication immediately. If your pet continues to experience side effects despite the anti-nausea medication we prescribed, please contact our oncology department. We may recommend outpatient care or additional medications. In addition, do not give any food for 12 hours, and offer ice cubes or very small amounts of water every few hours. After 12 hours, feed small portions of bland food frequently (instead of one large meal). You can add warm chicken broth and a small amount of your pet’s favorite foods to increase flavor and appeal.  

 

• Vomiting: Most often, vomiting is preceded by signs of nausea (see above). However, you may note vomiting without signs of nausea. If you have not administered the anti-nausea medication, give it immediately. If you’ve already administered the anti-nausea medications we prescribed and your pet has still vomited, do not give any food or water for 12 hours. If your pet seems hungry and is no longer nauseous, you can start offering small amounts of bland food on an hourly basis (boiled chicken or low-fat ground turkey, cooked white rice, low-fat cottage cheese). Vomiting once or twice without other signs or fever should be reported to us but does not usually require further treatment. Frequent vomiting may require fluid therapy administered by a veterinarian, parenteral (not oral) anti-nausea medications, or additional supportive medications. If at any point your pet continues to vomit despite withholding food/water or at any point your pet appears lethargic or depressed, your pet needs to be evaluated either with your local vet or us as soon as possible.  

 

• Diarrhea: If your pet develops loose stools or diarrhea, administer the metronidazole we prescribed. Keep water available at all times. Diarrhea without vomiting or fever can usually be managed with metronidazole and a bland diet until stools are normal, then gradually switching back to regular dog food. Please call us if this doesn’t resolve in 36-48 hours.  

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Bone marrow suppression: 

The bone marrow is responsible for producing white blood cells, and when it is affected by chemotherapy, white blood cell counts may temporarily decrease to a nadir. Typically, this decrease occurs 7 days after a chemotherapy dose, but the timing may vary depending on the drug.  Decreases in the white blood cell count may be mild, moderate, or severe.  Because the body regenerates these cells very quickly, even if your pet experiences a very severe drop in their levels, the count will usually return to normal within 72 hours. 

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White blood cells are very important in fighting infections.  If the body has a very low white blood cell count, it is more susceptible to infection.  In this situation, normal bacteria found in your pet’s body can cause serious illness. Thankfully, most pets with low white blood counts feel well and have no clinical signs.  However, if an infection develops, he or she may develop a fever, refuse food, and appear lethargic. If you note these signs around 7 days after chemotherapy is administered, this is a medical emergency and requires hospitalization to keep him or her safe and comfortable. If you are concerned for any reason, you can take your pet’s temperature rectally. If the temperature is above 102.5 at rest or if you are concerned, please call us and plan to bring your pet in to our hospital for evaluation. Even if your pet’s temperature is normal, he or she could still be fighting a severe infection, and evaluation by a veterinarian is still advisable.  

Regardless of how your pet feels, we routinely check blood cell counts at the expected nadir (the time when white blood cell counts are lowest) and before every chemotherapy treatment to evaluate how your pet’s body is managing chemotherapy. If the white blood cell count is very low, or if fever is present, the addition of antibiotics and fluid therapy may be indicated. If the white blood cell count is very low and your pet is feeling well, we will advise you to avoid places where your pet could be exposed to potential infections (public areas where many dogs pass through, such as parks, grooming facilities, and boarding facilities).  

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Miscellaneous Side Effects: 

 

Hair loss: Most pets receiving chemotherapy will not experience hair loss. Cats may lose their whiskers and longhaired cats may lose their outer coat.  Dogs may develop mild hair thinning.  Spots where hair is clipped for surgery or chemotherapy administration may grow back very slowly.  However, some dog breeds are more likely to experience hair loss due to chemotherapy.  If you own a Poodle, 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 a more significant amount of hair during the initial stages of chemotherapy.  For all pets, hair will grow back once chemotherapy is completed or treatments are given less frequently.  Sometimes hair may grow back a slightly different color or texture.  

 

Skin and tissue damage: Some chemotherapy drugs can be extremely irritating to the skin and underlying tissues if they leak outside the vein during injection. Examples include vincristine, vinblastine, doxorubicin, and mechlorethamine.  Severe swelling, ulceration, and inflammation are evident.  However, this complication is rare because chemotherapy at our facility is administered by highly trained, oncology-specific technicians who strictly adhere to the most recent national safety guidelines. 

 

Some chemotherapy drugs have unique toxicities.  These will be explained to you if your pet receives one of these medications, and appropriate steps will be taken to avoid them.   

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What should I expect at my pet’s chemotherapy visit?  

Prior to each dose of chemotherapy, we will discuss how your pet has been feeling with you and perform a physical exam.  Periodically, additional diagnostics such as X-rays, an ultrasound, or a CT scan may be needed to determine whether or not the chemotherapy drugs are effective in treating your pet’s cancer.  In addition, a blood sample is drawn to check the white blood cell, red blood cell, and platelet counts. Depending on the chemotherapeutic agent, additional lab tests may be required. This is necessary to ensure it is safe to proceed with treatment.  In some cases, your pet’s treatment may be postponed a few days due to a low white blood cell count.  Once it is determined that your pet may receive treatment, the drug is administered by the appropriate route (oral, intravenous, or subcutaneous).  The time of infusion for intravenous drugs varies from a few seconds to all day depending on the drug being administered.   

 

Chemotherapy appointments are scheduled as “drop-off” appointments to allow us adequate time to assess your pet, review the blood work, and administer the needed drug.  Please drop your pet off before 9 am and expect to pick them up in the afternoon.  At the time of drop-off, one of our technicians will meet with you to discuss how your pet has been feeling and will help you to fill out a form.  Please leave a phone number so that we can reach you during the day if needed.  After the pet has been assessed and treated, we will call you to let you know when to pick up your pet.  Most pets go home in the afternoon, but if it is more convenient for you to pick up your pet after 5 pm, that can be arranged.   

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How long will my pet receive chemotherapy? 

The length of a particular course or protocol of chemotherapy will vary depending on the disease being treated and your pet’s response.  For some patients, a particular chemotherapy protocol is administered, and once this is completed, no additional treatment is required.  For these animals, we recommend recheck evaluations through our oncology service or your family veterinarian to periodically check for recurrence of the cancer.  Early detection of recurrence (i.e. before the cancer becomes too advanced) provides more treatment options with a greater potential for success. 

For other types of cancers, pets receive longer-term chemotherapy.  In these cases, we administer a particular agent until it is no longer effective in killing cancer cells.  When the pet’s cancer becomes resistant to a drug, we administer a different chemotherapy drug for as long as it is working.  In these cases, we cannot predict how many doses of a particular drug a patient will receive.  We continue treatment as long as the pet is feeling well and has a good quality of life.  

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What happens if I have an emergency? 

If you have any questions or concerns about your pet after chemotherapy is administered, please call the oncology service at Ally Veterinary Specialty Center at (781)790-0805 to speak with a veterinarian or a technician.  We are open Monday through Thursday 8 am – 5:30 pm. If the oncology staff is not available, please contact Blue Pearl Hospital at (781) 684-8387 for urgent advice.  You can also contact your family veterinarian.  

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Is it safe to be around my pet while he or she is receiving chemotherapy?  

Generally speaking, the risk to a person handling their pet that is receiving chemotherapy is very low. We do not recommend changing your or your pet’s lifestyle as a result of chemotherapy treatments.  This means that they may continue to sleep in your bed, do not need to be separated from other household pets, can continue to share a litter box with other household cats, and may even eat their normal breakfast the morning of their chemotherapy treatments.   

 

However, because repeated, long-term exposure to chemotherapy drugs can result in severe health problems, some precautions are necessary.  A small amount of chemotherapy may be excreted in your pet’s urine and feces for up to 72 hours after a dose of chemotherapy is given.  It is important to avoid contact with your pet’s urine or feces during this time.   

• Take care that your pet does not urinate or defecate in high-traffic areas, such as around playing children. If possible, leash-walk your pet to one area of the yard for the first 3 days after chemotherapy treatment to decrease exposure of the yard to contaminated waste, and keep family, visitors, and other pets away from this designated area.  

• Any time you need to handle bodily waste, wear latex gloves, “peel” the gloves off afterward so they come off inside out, place the waste and gloves in a plastic bag (e.g., zip-lock bag), double-bag, dispose of it in the trash, and wash your hands. Always immediately take the trash out.  

• If you need to clean up an “accident” (urine, feces, vomit) in the home, wear gloves, use disposable absorbent materials like paper towels (or old towels you don’t mind throwing away), and put them in a plastic bag in the trash. Always immediately take the trash out. Bleach is the most effective cleaner for chemotherapy drugs. If bleach is not an option for the surface, other soaps or cleaners can also be effective.  

• If clothes or bedding are soiled, launder them separately from other laundry. Use bleach and double wash with hot water and detergent.  

• Children, lactating women, and women who are or may be pregnant should not handle the urine, stools, saliva, blood, or vomit of a pet that has received chemotherapy within the past 3 days and should consult with the obstetrician or family physician.  

• For cats, use dust-free litter and clean the litter box often. Dispose of litter in a closed plastic bag. Keep children away from the litter box. Completely change the litter 3 days after chemotherapy treatment.  

• If you, a family member, or another pet accidentally contacts bodily wastes, don’t panic. Wash off the contacted area with soap and water. Even with the drugs that are excreted in the highest concentration, excretion occurs over longer periods (hours to days), so the amount in any single urination or defecation will be a fraction of the dose your pet received, and the amount that actually gets on your skin is a small fraction of that; and only a very small percentage could possibly penetrate the skin. For any concerns, please consult your physician. 

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Are there any special precautions I should take if I give oral chemotherapy to my pet at home? 

Always wear gloves when handling chemotherapy pills and wash hands thoroughly when administration is complete.  For dogs and with most chemotherapeutics, you can put the pills into a “meatball” of tasty food and give the pill before the pet’s meal when he or she is most hungry.  Unfortunately, this does not work for cats, and you often have to pill them.  Please ask your oncologist or a technician for a demonstration of how to administer a pill to your pet if you are unsure. 

 

Please adhere to the following guidelines:    

• Administer the drug only in the prescribed dose and frequency. 

• Prevent direct contact of the drug with your skin. Always wear disposable gloves (nitrile or latex) when handling your pet’s medication; “peel” the gloves off afterward so they come off inside out and dispose of them in a closed plastic bag (such as a zip-lock bag) and put the bag in the trash. Wash your hands with soap and water afterward. 

• Make sure your pet swallows the medication entirely and does not chew it or spit it out.  

• Never split or break tablets, and never open any capsules.  

• If you need to place the medication directly on a surface, use something disposable (e.g., a paper towel or a piece of kitchen foil), then dispose of it afterward.   

• Store your pet’s medication away from food areas and in its original container.  

• Keep all medication, containers, and waste well away from children.  

• Lactating women and women who are or may be pregnant should not directly handle chemotherapy medication, should not be in the room when chemotherapy is being administered, and should consult the obstetrician or family physician.  

 

This information sheet was prepared by Dr. Custead at Ally Veterinary Specialty Center.  It is a modification (with permission) of a document used at the University of Georgia College of Veterinary Medicine. 

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