Thyroid Cancer (Adenocarcinoma) in Cats

By PetMD Editorial on May 27, 2009

Thyroid Gland Adenocarcinoma in Cats

The importance of the thyroid gland is many fold. It is responsible for a variety of bodily functions, most notably the coordination of hormones and normal metabolism. Adenocarcinoma of the thyroid gland is like other adenocarcinomas: it grows rapidly and can metastasize to other parts of body. Adenocarcinoma of the thyroid is more commonly seen in older cats, but young cats may also suffer from this neoplasm.

The element iodine is also suspected of playing a role in the dysfunction of the thyoid gland. Because iodine is essential for the thyroid to work properly, cats living in iodine deficient areas may be at higher risk of developing these neoplasms.

Symptoms and Types

Following are some of the symptoms commonly related to adenocarcinoma of the thyroid.

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


The cause of thyroid adenocarcinoma is still unknown.


Your veterinarian will perform a thorough physical exam on your cat, with blood tests, biochemistry profile, and urinalysis. You will need to give a thorough history of your cat'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.


There is no curative treatment yet available for this neoplasm of the thyroid gland in cats. Surgery may be employed for partial or complete removal of the thyroid gland, along with the neoplastic tissue. As this area has an extensive blood supply, it is possible for hemorrhage to occur during surgery, requiring a transfusion of blood to the patient. Other protocols used for treatment of a thyroid gland adenocarcinoma include radiotherapy and chemotherapy. If the thyroid gland is removed, your veterinarian may prescribe the iodine supplement thryoxine to be given orally to your cat in order to maintain other body functions that are dependent upon thyroxine. Thyroxine supplementation will be given for the life time of your cat.

Living and Management

Cats that have been treated for thyroid adenocarcinoma should be encouraged to rest if activity causes breathing problems. As much as possible, keep your cat in a low stress environment. The heart rate in these patients tends to fluctuate, so your cat may collapse unexpectedly at any time. Contact your veterinarian immediately in such a situation. Follow your veterinarian's treatment guidelines, especially in giving the chemotherapeutic agents at home. Many chemotherapeutic agents can be hazardous to your health if not handled properly, consult with your veterinarian on the best handling practices.

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