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Thyroid Cancer in Dogs

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Lili Duda, VMD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
Would you please direct me to information regarding thyroid cancer in dogs?

I appreciate your time and effort.  
Thank you very much.
J

Lili Duda, VMD, Editor of the OncoLink Veterinary Oncology Section, responds:

Thank you for your interest and your question.

Thyroid tumors in dogs are generally malignant. They are called "adenocarcinomas". These tumors tend to occur in older dogs. Male and female animals are equally affected. These tumors have a moderate metastatic rate (meaning they can spread to other organs, particularly the lungs).

For small tumors that are freely moveable and can be completely removed at surgery, long-term tumor control may be achieved. Chemotherapy may be indicated to control microscopic amounts of tumor that may have spread to other areas of the body. For dogs that have large tumors that are "fixed" or attached to underlying tissues, the prognosis is not as good. Radiation therapy to the tumor site can help provide tumor control after surgery, or can be used to shrink down a tumor prior to surgery. However, large tumors are much more likely to have spread elsewhere, and chemotherapy is indicated in these cases.

For tumors that are too large for surgery, or that have evidence of spread to the lungs (or elsewhere), chemotherapy might provide some palliation (alleviation of symptoms). Chemotherapy is used in selective cases to hopefully shrink down the tumor enough to cause some improvement in clinical signs like difficulty breathing or swallowing. Unfortunately, these palliative effects are usually of short duration.

Also, if you have not already done so, please consult a veterinary oncology specialist. If there is not one in your area, most veterinary oncologists will be happy to provide a phone (or email) consultation TO YOUR VETERINARIAN. Most veterinary oncologists are unable to talk with clients directly if they have not actually seen the pet.