Written on November 14, 2012 by Staff Veterinarian

Frequently asked questions about Chemotherapy:

What is Chemotherapy?

The use of a drug or chemical to treat any illness is referred to as “chemotherapy”, but this term commonly refers to the use of drugs in the systemic treatment of cancer.

The ultimate goal of chemotherapy would be to cure the patient of cancer.  In most instances (and at this point in time in veterinary medicine), this is not a realistic goal.  Until we can cure cancer, our goals are to:

  • Control rapidly progressive disease
  • Prevent spread of the tumor
  • Restore deteriorated function
  • And provide a good quality of life during the time of remission.

The term “remission”  refers to the time interval during which there are no outward signs that the patient has cancer.  Unfortunately, it is not possible to predict which animals will achieve full remission, nor how long it will take and how long it will last if remission is achieved. Every patient and pet-owner relationship is different and is managed on an individual basis.

In appropriate situations, chemotherapy can be used to benefit pets with cancer.  Most pets tolerate chemotherapy well, do not realize that they are ill, and appear to enjoy their extended life.  However, each owner must believe that they are doing the right thing for their pet, in their situation.  If it were ever obvious that therapy was not working, or that the pet was experiencing pain or discomfort, we would work with you to discuss any changes in the treatment plan, and tailor a new approach, as needed.


How Does Chemotherapy Work?

Cancer cells generally multiply very rapidly.  Most chemotherapy drugs work by damaging rapidly growing cells (including both cancer cells and some normal cells in the body).  Different drugs interfere with different steps in the process of cell growth and division.  This decreases the ability of these rapidly growing cells to divide, and kills them.

Some newer chemotherapy drugs (called targeted therapies) have been designed to attack more specific targets that may be found on certain cancer cells.  In many cases, a combination of drugs is the most effective way to kill the cancer cells. Your pet’s treatment dose and schedule will depend on the type of cancer and the chemotherapy method.

How is Chemotherapy Given?

The oncologist will examine your pet and consult in detail with you and your regular veterinarian. Together a decision will be made about whether to pursue chemotherapy (based on your pet’s type of cancer and prognosis) and which protocol would best be applied.

If chemotherapy is given to your pet, our veterinary oncologist will tailor the course of therapy carefully.  Treatment for each patient is individually managed, although specific chemotherapy protocols consisting of several different drugs are followed for different types of cancer.

The majority of chemotherapy drugs are given by intravenous injection, but some are given by mouth. Prior to each treatment a blood sample will be drawn. The white blood cell count, red blood cell count, and platelet count will be checked to ensure that it is safe to proceed with treatment; in some cases, your pet may not receive treatment due to a low white or red blood cell count.

The route chosen depends on the type of cancer being treated and how well the therapy is tolerated by the patient. Treatment may be prescribed on a daily, weekly or monthly basis.  The specific length of your pet’s individual course of treatment will be discussed in detail with you.


Will My Pet Experience Side Effects?


Chemotherapy is a word that creates an instant emotional response in everyone.  Visions of debilitating nausea, vomiting, coupled with loss of hair and lack of energy are associated with the term. However, the reality of chemotherapy for animals is much different than that of human cancer patients.

For animals receiving chemotherapy, quality of life for the patient is the primary concern for us and for each pet’s owner.  Doses of drugs and treatment schedules are designed to minimize discomfort to the patient, while providing the most effective defense against the disease.  As a result, most people are pleasantly surprised at how well their pets feel while undergoing chemotherapy.

Ideally, the animal receiving chemotherapy does not even realize that he or she is ill, and most of our patients do not have side effects with treatment.  The drugs used in chemotherapy, however, are extremely potent and side effects can occur in about 20-30% of animals who receive chemotherapy treatment.  The potential for side effects must be balanced against the benefits of the chemotherapy and the side effects of the cancer if left untreated.  Choosing chemotherapy for your pet is an individual decision.


What Are the Most Common Side Effects?

The most common side effect reported by owners is that their pet seems to be “off” for a day or two.  This might mean that he or she has slightly less energy or seems less excited about eating, than usual. Less commonly, he or she may skip a meal or two, have one episode of vomiting or diarrhea, or seem unusually lethargic.

Unfortunately, there is no way to predict whether your pet will develop serious reactions.  The animal receiving chemotherapy needs to be watched closely and will need to be taken to his or her veterinarian at the first sign of illness.  Although serious side effects can occur with any chemotherapy, there is less than a 5% chance that a patient will be hospitalized with side effects, and less than a 1% chance of fatality caused by overwhelming infections.


What Other Side-Effects May Occur?

Practically all anti cancer drugs have side effects.  These side effects arise because the normal cells in the body are also exposed to the anti cancer drug.  The most sensitive normal cells are found in the blood, gastrointestinal tract, skin, and reproductive system.  Consequently, potential side effects include infections, bleeding, decreased appetite, vomiting, diarrhea, thin hair coat or skin color changes, and sterility.

Rare side effects associated with specific drugs include bladder discomfort, kidney damage and heart failure.  Although serious adverse effects can occur with any chemotherapy, there is less than a 5% chance that a patient will be hospitalized with side effects and less than a 1% chance of fatality caused by overwhelming infections.  However, in general the potential benefit of treatment with anti cancer drugs outweighs the possible side effects.  Below are listed some of the potential side effects of many chemotherapeutic agents in more detail:

  • Nausea (and refusal to eat) can occur in veterinary patients, and seems to occur more frequently in cats than in dogs.  If this happens, it usually occurs 2-5 days after treatment, and it is usually transient requiring no specific treatment.  Tempting the pet with favorite foods, and warming the foods slightly will often increase the liklihood that he or she will eat.  If this condition persists, medication to reduce nausea and promote appetite can be used.
  • Vomiting can also occur during treatment; also typically 2-5 days after a treatment has been given.  If your pet vomits once or twice, and otherwise seems bright, active, and alert, withhold food and water for 12 hours and then reintroduce water.  If your pet does not vomit after drinking water, you can offer food.  If the vomiting is repetitive (more than 3-4 times) or contains blood, if vomiting resumes with feeding, or if your pet is lethargic, weak, or depressed, consider bringing him or her to your vet, he or she may need medical attention.
  • Diarrhea may occur, but is often mild and transient. If stools are soft, feed bland food (boiled chicken and rice) for dogs.  If the diarrhea is bloody, watery, persists for more than 24 hours, or if your pet is lethargic and has diarrhea, veterinary attention is required.
  • Hair Loss (Alopecia): Pets rarely lose their hair, but if they do, they are not bothered by it as much as people are.  In most pets, hair does not grow continually throughout their lives like it does in people; therefore, hair loss in pets is rare.  Exceptions are certain breeds of dogs, such as poodles, Old English Sheepdogs and other breeds whose hair grows continually.
    In general, if a pet needs to visit a groomer periodically to be clipped, then the pet may experience some degree of hair loss as a result of chemotherapy.
    Cats may, however, lose all or most of their whiskers.
  • Reduction in the Number of White Blood Cells (Neutropenia):There are various types of cells in the blood.  The decrease in the number of infection fighting white blood cells is known as neutropenia.  Many chemotherapeutic agents impair the body’s ability to produce these white blood cells.  As a result, neutropenia may occur seven to ten days after chemotherapy.Neutropenia, alone, is not a danger to a patient.  However a patient’s ability to fight off infection is impaired by neutropenia.  Prior to each dose of chemotherapy, we perform a complete physical exam and a blood test called a complete blood count (CBC) to make sure it is safe to administer the next chemotherapy treatment. Should the patient have a significant reduction in the number of white blood cells, the doctor may want to delay chemotherapy treatment and/or prescribe antibiotics to protect against infection.
  • Hematuria (bloody urine):One of the chemotherapy drugs that we use Cytoxan (cyclophosphamide) may occasionally cause hematuria (bloody urine) in dogs.  If this occurs, you should discontinue the medication immediately and contact us by phone. This side effect is specific to Cytoxan (cyclophosphamide).  If bloody urine occurs and Cytoxan (cyclophosphamide) is not being used, contact us or your regular veterinarian for evaluation.
  • Fever/Sepsis: Virtually all chemotherapeutic drugs can temporarily suppress the body’s ability to fight infections.  If the white blood cell count (specifically neutrophils) drops too much your pet runs the risk of developing a systemic infection.  Your pet will usually develop a fever (but not always).  If the bacteria travel through the bloodstream, it is known as sepsis.  In rare cases, shock can occur (septic shock), and without rapid treatment, the risk of death is high.  Though this period of susceptibility is brief, and occurs at a fairly predictable time, its consequences can be life threatening. Signs of fever or sepsis include:
    • Fever greater than 103F: (temperature is taken by a rectal thermometer and should normally be between 99F and 102.8F). If you think your pet may have an infection, you may check your dog’s temperature rectally at home (cats usually will not tolerate this).  A digital thermometer is easiest to use; if it is 103 degrees or higher, please call us.  If signs of an infection are noted, we will recommend that you bring your pet to the hospital for examination and treatment as soon as possible.  This situation can be treated rapidly and almost always successfully. However, an extended delay before initiation of treatment may result in health complications or even death.  We can see your pet at any time of the day or night if you suspect your pet has an infection.
    • Extreme lethargy: Refusal to get up off pet bed, etc.
    • Complete disinterest in food
    • Extreme weakness
    • Pale and somewhat sticky gums
    • Severe vomiting and/or diarrhea
  • Allergic Reactions: Allergic reactions to chemotherapeutic agents are rare and generally will not be something you have to treat at home.  Should a patient have an allergic reaction, it usually develops upon administration and would be treated at the hospital. However signs to look for at home are :
    • a red muzzle/ears
    • scratching/pawing at the face
    • hives
    • vomiting.
  • Heart Damage: In rare cases, some chemotherapeutic agents, such as Adriamycin (doxorubicin), can irreversibly damage the heart muscle.  The dose of these agents prescribed for most dogs is below the dose that usually causes heart disease. Fewer than 10% of patients develop heart disease as a result of chemotherapy.  We may recommend a cardiology consultation prior to administering Adriamycin (doxorubicin) in dogs that have preexisting heart disease or that are at increased risk of heart disease (such as Dobermans, Boxers, and Great Danes).


Chemotherapy Precautions

If your pet is receiving chemotherapy, the following precautions should be followed.  In some cases these precautions are not necessary, but it’s best to establish a safe routine.  When in doubt, it is always better to be overly cautious!

Generally, it is safe to have unlimited contact with your pet during chemotherapy.

  • Avoid physical contact with your pet’s urine and feces for 48-72 hours after each chemotherapy treatment (depending on the drug administered).
    • Wear gloves when picking up your dog’s stool or when cleaning your cat’s litter box.
    • Double-bag the waste (for safety) and throw it into the garbage.
    • If your pet urinates or defecates in your home, wear gloves when you clean the area.
    • You can use a regular household cleaner when cleaning the area.
  • Always wear gloves when handling tablets of chemotherapy.  Prednisone, antibiotics and drugs to prevent nausea/diarrhea can be handled safely without gloves.
  • Never split chemotherapy pills.
  • Store pills safely out of the reach of children and pets.
  • Pregnant or nursing women, people actively trying to conceive (both men and women), immunosuppressed individuals, and children should avoid all contact with chemotherapy drugs and the waste from pets treated with chemotherapy.

What Happens After Treatment is Over?

It is important for your veterinary oncologist, or your regular veterinarian to examine your pet periodically after chemotherapy is over, usually at 1 –2 month intervals.  This will allow potential problems, such as recurrence of the cancer, to be detected before they become 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 owners of pets who have had chemotherapy to realize that the cancers we treat are rarely cured.

Almost all of our patients ultimately have recurrence of their cancers. However, it is vital to understand that most pets 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  majority of owners tell us that they have no regrets about their decision to pursue chemotherapy for their pet.

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