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Thyroid Gland Adenocarcinoma in Dogs

The thyroid gland is responsible for a variety of bodily functions, most notably the coordination of hormones and normal metabolism. A particularly malignant form of cancer, carcinoma is characterized by its ability to spread quickly throughout the body. Adenocarcinoma is differentiated only in that it originates in the glandular tissue. Adenocarcinoma of the thyroid gland is a malignant tumor, which can metastasize to other tissue and organs, including the lungs. As iodine is essential for the thyroid to function normally, this neoplasm has been found to be more prevalent in iodine-deficient areas.

Although any breed may be affected, boxers, beagles, and golden retrievers have been found to be at higher risk than other breeds of dogs. Like other carcinomas, it is most commonly seen in older dogs, but it may also occur in young animals.

Symptoms and Types

Following are the symptoms commonly related to adenocarcinoma of the thyroid:

• Large fixed or movable mass over dog’s trachea covering larynx
• Dypnea (difficult breathing)
• Dysphagia (difficulty in swallowing)
• Weight loss
• Dysphonia (hoarseness)
• Polydipsia (increased thirst)
• Polyuria (increased amount and/or frequency of urine passing)

Causes

The cause of thyroid adenocarcinoma is still unknown.

Diagnosis

Your veterinarian will perform a thorough physical exam on your dog, with blood tests, biochemistry profile, and urinalysis. You will need to give a thorough history of your dog's health and onset of symptoms. The most informative and helpful test is the T4 (thyroxine) and/or free T4 concentration determination. Thyroxine is a primary hormone produced by the thyroid gland. Its level tends to increase in some patients with adenocarcinoma of the thyroid gland. Thyroid Stimulating Hormone (TSH) levels will also be determined, along with T4. TSH is another hormone released from the brain which controls the release of T4 hormone. X-ray and ultrasound imaging, computed tomography (CT) scan, and magnetic resonance imaging (MRI) are some of the diagnostic tools your veterinarian can use to confirm the diagnosis and to determine whether the tumor has metastasized. Your veterinarian may also perform a biopsy of the thyroid tissue to see if malignant cells are present in the thyroid gland.