Diagnosing Canine Thyroid Carcinoma

Malignant canine thyroid tumors are fairly common in dogs. There are a number of factors that determine which dogs are susceptible, and prognosis will vary from case to case. Some cases can be cured completely, while others may be terminal. Catching the cancer early is the only definite path to long term survival.

How Thyroid Tumors Develop

The development of tumors in the thyroid is not a straightforward process, and several factors must come together before cancer can form. First is the genetic factor: certain dogs are simply at greater risk due to their genetic makeup or pedigree. Species such as beagles, golden retrievers and boxers are reputed to have a higher susceptibility to developing a cancer.

Age is another factor. Older dogs are at a greater risk for developing cancer, as cancer is often born from mistakes in the DNA during cell division. The more divisions that have taken place, the greater chance there is for a mutation to occur that is cancerous in nature. Some tumors that are non-cancerous may form out of inactivity in the thyroid. Colloid goitre can occur in hypothrydoid dogs, and often occurs when tumors in the pituitary gland suppress the ability of the thyroid gland to produce the correct amount of hormones.

A prolonged or over-stimulation of the thyroid gland may lead to hyperplasia, an overgrowth within certain areas of the thyroid. These will first form a benign form of cancer, but will then turn malignant as the growth continues. Such malignant growth is known as thyroid adenocarcinoma.

Thyroid Carcinoma Symptoms

The symptoms of thyroid carcinoma are non-specific, and testing is the only definitive way to acquire an accurate diagnosis. Frequent blood and urine tests may be used to establish the presence of a thyroid tumor. Several thyroid diseases may cause similar symptoms, and the most common symptoms include:

  • Visible mass in the neck
  • Coughing
  • Difficulty breathing
  • Difficulty Swallowing
  • Dysphonia
  • Weight loss
  • Vomiting
  • Anorexia / decreased appetite

Thyroid carcinomas may extend into the esophagus, trachea and larynx. They may even invade the muscles of the neck, the nerves and surrounding blood vessels of the thyroid gland.


Treatment largely depends on the type of tumor present in the dog's thyroid. There are two types:

  • Movable Tumors. If the thyroid tumor is movable, this means it can likely be extracted in surgery. Movable tumors do not generally invade surrounding organs and tissues, and have a better prognosis. However, even with surgery, external beam irradiation and radiotherapy may be necessary to completely cure the cancer.
  • Fixed Tumors. Also called malignant thyroid tumors, fixed tumors have spread into the surrounding areas. These are much more difficult to move, and are known as bilateral thyroid cancer. It generally does not carry a good prognosis. Often the only way to treat these types of tumors is through chemotherapy or radiotherapy.

Approximately nine of 10 thyroid tumors are malignant and it is too late to completely remove or cure them. The longer the tumor remains in the body, the more fixed it becomes and the more difficult to remove. Early removals yield better results and a longer overall survival rate.

It is rare, but not unheard of, for the cancer to disappear without any treatment. A lack of blood supply to the tumor will sometimes cause this; however, even when the cancer appears to be gone it may not be totally eradicated and may recur.

Canine thyroid carcinoma is a common disease found in dogs, and treatments are available. However, since many of the cancer cases are caught when it is too late, early check ups at the first signs are recommended, to help catch and remove tumors before they become life-threatening.