Thyroid Cancer Symptoms in Dogs

Thyroid cancer symptoms can be difficult to detect because they often involve minor manipulations of hormones produced by the thyroid gland. Fortunately, though thyroid problems are common in dogs, thyroid cancer is rare. Thyroid cancer is more common in certain breeds, including boxers, beagles and golden retrievers.

Role of Thyroid

The thyroid gland, located in the neck just below the larynx, is a part of the endocrine system and releases hormones T3 and T4 that control many different processes in your dog's body. The thyroid plays a role in growth of young dogs and a role in regulating energy and metabolism as your dog grows older. Thyroid hormones also help your dog's body break down fat and control how much oxygen and calcium are released into the tissues.

Symptoms of Thyroid Cancer

The most common symptom of thyroid cancer is an enlarged thyroid gland, which can often be observed at the base of your dog's neck. This is caused by the tumor preventing hormones from being released. However, because thyroid hormone production is regulated by the pituitary gland, the thyroid continues to produce the hormone, which results in swelling. This may lead to difficulty breathing or swallowing.

Additional symptoms can mimic hyperthyroidism or hypothyroidism, which are over- or under-production of thyroid hormones. These symptoms include:

  • change in appetite
  • weight gain or weight loss
  • anxiety
  • change in energy level

Diagnosis of Thyroid Cancer

The difficulty in diagnosis is that if the thyroid doesn't swell, symptoms usually mimic hyper or hypothyroidism, which will likely be your veterinarian's first course of treatment. Traditional blood and urine tests will likely confirm thyroid disease but may not lead your veterinarian to diagnose cancer unless treatment is ineffective.

Nearly 90 percent of thyroid tumors are malignant, and many go undetected until the cancer has spread to other areas of the body, particularly the lungs. Unfortunately, the only definitive diagnosis may require X-rays to detect the lump, and a biopsy to determine if it is malignant.

Treatment of Thyroid Cancer

The most common treatment of thyroid cancer is surgery to remove the tumor. If this is possible without damaging organs or major blood vessels, this will be the first choice whether the cancer has already spread or not.

If surgery is not possible, radiation treatment, which consists of using radiation to shrink the tumor, is also an option. Surgery still might be necessary once the tumor has been shrunk to an operable size.

If the tumor has spread, or even if it hasn't, chemotherapy may also be required. Chemotherapy works similarly with dogs as humans, killing all of the cells in your dog's body, both cancerous and healthy. This results in a number of negative side effects, which are often milder in dogs because veterinarians use smaller dosages than used in humans. It's important to work with an experienced oncologist to ensure that your dog is getting the correct drug combination and dosage.

Though thyroid cancer is difficult to detect, if caught early, the treatment success rate is high. If your dog is showing symptoms, visit your veterinarian immediately.