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There are typically two main avenues of chemotherapy for treating mast cell tumors in dogs: the more “traditional” chemotherapy drugs (e.g., CCNU, vinblastine, prednisone), and the newer class of drugs called tyrosine kinase inhibitors (Palladia and Kinavet).

Traditional chemotherapy drugs work by causing damage to DNA within cells, without regard to whether the cell is a tumor cell or a healthy cell. This is the reason for some of the side effects seen with chemotherapy, including adverse gastrointestinal signs and lowered white blood cell counts.

The mechanism of action of tyrosine kinase inhibitors (TKIs) is very different. These drugs work primarily by inhibiting the action of a receptor on the surface of mast cells that is mutated in about 20-30 percent of tumors. When the receptor is mutated, it causes uncontrolled cell division, leading to tumor growth.

TKIs can also work by inhibiting the growth of blood vessels to tumor cells (this is called anti-angiogenesis therapy). This mechanism of action is separate from the previously mentioned mechanism, which means tumors without the specific receptor mutation may still have a good response to treatment.

TKIs are orally administered medications given continually at home. Dogs need to have “steady state” levels of these drugs in their blood stream to keep the receptor continuously turned off. The receptor is present on other cells in the body, so side effects can occur with TKIs as well, but are generally fairly limited in their spectrum.

The take home messages for canine mast cell tumors are:

  1. They are very unpredictable in their behavior.
  2. The biggest predictor of behavior is the grade of the tumor, which can ONLY be determined via biopsy.
  3. Staging tests are important to look for spread of disease and should include labwork, regional lymph node aspirates, an abdominal ultrasound, and in some cases, a bone marrow aspirate.
  4. Surgery is the mainstay of treatment for most dogs.
  5. Radiation therapy and chemotherapy play roles for dogs with mast cell tumors — consult a veterinary oncologist to be sure you know all the options available for treating your dog!

Dr. Joanne Intile

Image: JPagetRFPhotos / via Shutterstock

Comments  5

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  • Labwork
    06/26/2013 05:44pm

    "These drugs work primarily by inhibiting the action of a receptor on the surface of mast cells that is mutated in about 20-30 percent of tumors."

    Could a really good pathologist be able to tell if the receptors are mutated? If not, how could one determine if that is the case?

  • 07/01/2013 03:53pm

    Hi

    You asked a great question. The mutation in the receptor can be detected through advanced molecular testing that can be request on the original biopsy sample. This testing is not routinely done, so it is something I discuss with owners when they come to appointments.

    Joanne

  • 06/27/2013 04:23am

    Thanks a million! God bless you for the information and facts related to cancer and its treatment! Cancer is considering being the leading cause of death in dogs, your valuable info will help the Dog owner to meet with the vet having some sort of view for chemo treatment.

  • 07/01/2013 03:54pm

    Thank you for your kind words!

  • Treatments for Mast Cell
    03/04/2014 03:40pm

    In addition to the various types of chemotherapy is there a reason that an oral antihistamine wouldn't be helpful? Is there any very current research on the success rates with the TKI drugs?

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