Thyroid Cancer in Dogs if Left Untreated


Thyroid cancer is related to thyroid gland which is located in the middle of the dog’s neck along its windpipe. Thyroid cancer is diagnosed when you notice a mass or lump on your pet’s neck. This is a thyroid tumour and it develops because of abnormal growth of cells in thyroid gland. Thyroid cancer in dogs if left untreated can lead to the cancer spreading and causes other complications. Having information about your dog’s general health helps in taking better care.


These tumours can be benign or malignant. Benign tumours are harmless non-cancerous growths. Malignant tumour is a cancerous lump and is known as carcinoma and adenocarcinoma. Sometimes along with development of thyroid tumour, the functioning of thyroid hormone is also affected in dogs. However, this is rare so, most thyroid tumours in dogs are non-functional. If the thyroid tumour is classified as functional, the thyroid hormone gets produced in excess, leading to hypothyroidism or hyperthyroidism.

Thyroid Cancer in Dogs

What happens if it is left untreated?

Since thyroid tumours in dogs are mostly found to be malignant, they will keep growing in case thyroid cancer in dogs if left untreated. Slowly, this abnormal growth spreads to other tissues as well. This condition is known as metastasis. A large number of tissues eventually get metastasized in about 65%-90% of dogs with thyroid tumours. This means the dog continues to suffer and it could lead to its death.

Thyroid cancer signs in dogs

When the cancerous lump is identified, it is already growing and spreading in the body. It may still be treated, if you notice the symptoms and take it to the vet for diagnosis.

  • First thing you may notice is the presence of a lump in neck which may be fixed or moving
  • If the growing mass compresses the trachea in the neck, the dog may have cough
  • Your dog may experience shortness of breath or breathe rapidly
  • She may have difficulty in swallowing food and may also gag
  • You may notice a change in her bark
  • The dog may lose weight owing to lack of appetite
  • In case of hypothyroidism accompanying tumour, your dog may become inactive, lose hair and become exercise intolerant.
  • In case of hyperthyroidism, she may have a huge appetite, thirst and shivering of muscles.

Treatment options

Treatment depends on factors concerning the size of the mass, its metastasis and whether thyroid hormone is affected. Surgery may be recommended to remove tumours in some cases, but it depends on the tumour’s location and its depth of growth. Sometimes surgery alone may not be enough to ensure cancer is removed from body. Because by the time cancer is diagnosed, the tumours are already large and probably spread to other tissues as well. Additional procedures may include radioactive iodine therapy, chemotherapy and radiation.


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