Dog: Thyroid Cancer

General information

Other common/scientific names: thyroid tumors

The thyroid glands in the dog are located on either side of the trachea (windpipe) and exist as two separate halves. While thyroid cancer in dogs can be either benign (adenoma) or malignant (carcinoma), these tumors are generally malignant. The cancer can affect one or both sides of the thyroid gland. This type of cancer tends to spread to the surrounding areas of the throat, the lymph nodes and lungs.

Thyroid cancer usually affects older dogs (>9 years). Boxers, Beagles and Golden Retrievers are more prone to developing thyroid cancer.

Cardinal symptom

Enlarged thyroid gland


Thyroid tumors can be very small or quite large reaching up to five inches in diameter. Large tumors can cause swallowing difficulties and a change in the dog’s voice or bark. Tumors which are invasive and adhered to the underlying tissue may cause pain and breathing difficulty.

Although most thyroid tumors do not affect the production of thyroid hormones, some may cause clinical signs associated with hypothyroidism while others will cause signs of hyperthyroidism.


Diagnosis of thyroid cancer is made by physical examination and sampling of the tissue for identification of the cells. A fine needle aspirate or a biopsy can be used to obtain tissue samples. Ultrasonography and radiography is used to determine the size and extent of the tumor. Radiographs should be taken of the chest to check for spread of the cancer. Scintigraphy (nuclear medicine) and magnetic resonance imaging (MRI) are used at universities and referral hospitals to assess tumor size and metastasis.


Treatment of thyroid cancer will depend on the size of the tumor, extent of invasion, spread of the tumor and symptoms of thyroid disease. If the tumor is freely moveable without being adhered to deeper structures, surgical removal of the thyroid (thyroidectomy) is the treatment of choice. Chemotherapy and/or radiation can be used for palliative treatment of tumors too large for surgery, too tightly adhered or that have evidence of spread to other organs. These procedures are performed at universities or veterinary specialty referral clinics.


If the tumor is small, easily moveable and can be completely removed with surgery, the prognosis is good for long-term tumor control. However, in dogs, most cases of thyroid cancer are malignant and have already spread to other areas of the body, so the prognosis is poor. In these cases, any treatment aimed at reducing pain and clinical symptoms is usually of short duration.

Update version: 4/24/2014, © Copyright by
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