Chemotherapy is the treatment of cancer with anticancer drugs. These compounds are toxic to malignant cells. They are generally administered intravenously, but can also be given by mouth or by injection. Chemotherapy may be the only line of treatment, or it may be given in combination with other modalities. For cancers that are at high risk of spreading, such as hemangiosarcoma, chemotherapy may be employed after surgery or radiation to help slow down the growth of cancer that may have metastasized or already spread. Chemotherapy is also used to shrink the size of a tumor prior to surgery or to increase your pet's comfort while living without the disease.

The goal of chemotherapy in veterinary oncology is generally to extend or improve the quality of life for an affected pet.

Chemotherapeutic "protocols" vary by type of cancer, the extent of the disease, the health of your pet, and any other known issues that are individual to your pet. Chemotherapeutic agents, for example, can affect certain breeds differently.

Route: Some chemotherapeutic agents are given intravenously over a period of time in the veterinarian's office. Others require a simple injection. Yet you may give others orally at home.
Frequency: Chemotherapy may be given daily, weekly, or once every three weeks. This allows the bone marrow to recover and produce more white blood cells.
Duration: The length of time your pet will be on chemotherapy depends on the type of cancer, the treatment goals you and your veterinarian have determined, and your pet's response to therapy. Some pets will remain on chemotherapy for the rest of their lives. Other pets may be able to conclude chemotherapy if it appears they are in remission.
Selection: Chemotherapy drugs are also used in combination. This often enhances the efficacy of the drugs, thus, allowing them to be used at a lower dose. Some tumors can also be resistant to a certain drug. Using a combination of drugs helps combat this issue, as each drug may work differently to fight the cancer. The selection of drugs used will depend on what the standard protocol is for your pet's particular cancer, as well as your veterinarian's recommendations regarding your pet's individual health status.

Compared to people, pets suffer fewer and less severe side effects from chemotherapy. This is primarily because veterinary oncologist use lower doses of drugs, and do not combine as many drugs as do human oncologists. All rapidly dividing cells in the body are sensitive to chemotherapy, and while cancer cells fall into that category, so do cells that are found in the intestinal tract, bone marrow, and hair follicles. Chemotherapy, therefore, may result in gastrointestinal upset, immune suppression, and hair loss in some pets.

Possible gastrointestinal effects include decreased appetite, vomiting, and diarrhea, which if untreated, can lead to weight loss and dehydration. These effects are often delayed by several days after treatment. Veterinarians can treat these problems with antinausea medications and appetite stimulants.

Immune-suppressive effects result when the bone marrow is no longer able to make as many white blood cells (called neutropenia) which in turn leads to an increased susceptibility to infection. Antibiotics may be prescribed as a preventative measure.

Some pets, just like some people, may lose their hair during chemotherapy treatment (known as alopecia). While this is less common in pets, it does happen. Whiskers are most commonly affected, especially in cats. Some breeds of dogs (e.g., poodles) are most affected by hair loss than others. Hair loss generally starts two to three weeks after chemotherapy begins. It may appear just in spots, as a general thinning, or the entire hair coat may fall out. Hair generally begins to grow back within a few weeks to a month after treatment ends.

While severe side effects are extremely rare, be aware that any animal can have an unexpected reaction to an agent.

At each chemotherapy visit, the veterinarian will physically examine your pet and blood will be taken. Blood tests will be conducted to monitor white blood cells and other parameters. Additional diagnostic tests, such as ultrasonography, may be scheduled as needed. Once the tests are reviewed and your pet is cleared for the next round of chemotherapy, administration will begin.

The goal of treatment is to provide you and your pet with the longest amount of time together, while still maintaining the highest quality of life possible for your pet.

Always closely follow your veterinarian's instructions regarding the safe administration of any chemotherapeutic agent at home. Wear latex gloves when handling drugs and never break or cut a chemotherapy tablet in two.

Store chemotherapy drugs out of the reach of children and other pets

Avoid direct contact with your pet's urine and feces for at least 48 hours after chemotherapy administration. It's a good idea to take your pet to a remote location in your yard in order to take care of business.

Part of your pet's recovery plan includes attention from the people your pet loves best. Apart from following the common sense recommendations above, don't be afraid to pet or cuddle with your friend.

The diagnosis of cancer in a beloved pet can be devastating. However, it is important to realize that, as in human cancers, many forms of this disease in animals can be treated, managed, and even cured. Early detection and specialized care are leading to increased survival and cure rates in almost all types of cancers that afflict pets.

Chemotherapy, alone or in combination with surgery and/or radiation, is one of the most effective ways to treat your pet's cancer. The main message that veterinarians and veterinary oncologist want to convey to owners today is that cancer can be successfully treated. Many owners are concerned about 'putting their pets through chemo.' The reality is that most pets handle chemotherapy very well.

Cancer treatment for both people and pets has become more sophisticated, and the side effects created by chemotherapy regimens have become less severe.

Chemotherapy administration in animals is less aggressive than it is in humans, so side effects, if encountered, are often very mild in pets. In humans, doctors seek to achieve a cure. In animals, the goal is to extend life while maintaining its quality. An additional 12-18 months of life for a dog is equivalent to several additional years for a human patient.

When side effects do occur, veterinarians have many options at their disposal to help keep your pet comfortable.

Most owners are pleasantly surprised at how well their pet does with chemotherapy, how good a quality of life their pet is able to maintain, and how gratifying it is to have the extra time with a treasured friend.


  • Make sure you schedule and keep all appointments.
  • Monitor your pet closely for signs of discomfort and report any changes to your veterinarian.
  • Provide your pet with plenty of 'comfort care'; a lot of attention and petting, a comfortable place to sleep, and more frequent trips outside for your pet to take care of business.
  • Pay close attention to diet. If your pet's appetite declines, try offering smaller, more frequent meals; add warm broth, bland meats or favorite foods to a meal; try hand feeding. Offer plenty of fresh water and monitor how much your pet is drinking.

If you have any concerns or questions at any time, please contact your pet's doctor so that he can help.