About halfway down a dog’s neck, along the trachea, are paired organs known as thyroid glands.
The tissue of the thyroid gland in the neck is the source of thyroid tumors. Carcinomas make up the majority of thyroid tumors. Bilateral thyroid tumors can occur in up to one-third of dogs. Rarely, a thyroid tumor that is “ectopic” may develop from tissue in the chest or another uncommon place.
The thyroid gland is in charge of producing thyroid hormone, which plays a crucial role in controlling metabolism. Only 10% of thyroid tumors really emit thyroid hormone that is functional, making them hyperthyroid. Thyroid tumors can range in size from being little and mobile to being big, invasive, and fixed to the surrounding tissues.
Thyroid Cancer in Dogs: Signs and Symptoms
A lump in the neck is the most typical symptom of thyroid cancer in dogs. Dogs occasionally have voice changes, swallowing issues, or quick, rough breathing. While hypothyroid animals might become lethargic, put on weight, and exhibit coat changes, hyperthyroid animals may experience weight loss and coat changes.
Diagnosing Thyroid Cancer
A biopsy or fine needle aspiration can be used to make a diagnosis. These tumors may have a rich blood supply, which may make it difficult to detect cancer cells in some samples and increase the risk of bleeding during a biopsy. When determining the level of invasiveness and possibilities for surgical removal, ultrasound and/or sophisticated imaging (CT/MRI) are frequently beneficial. The evaluation of potentially affected lymph nodes and the planning of radiation therapy can both benefit from a CT scan.
Bloodwork (including thyroid hormone levels) and imaging of the lungs are advised to check for potential metastases if a thyroid tumor has been identified (spread of tumor).
Conventional Treatment Options
For dogs with mobile thyroid tumors and those with limited invasion, surgery is advised. Because it is impossible to completely remove the tumor and there is a substantial risk of morbidity and mortality, surgical removal is not advised for dogs with deeply invasive or fixed thyroid carcinomas. Sometimes it is impossible to know whether a thyroid tumor can be removed before surgery.
For dogs with thyroid tumors that are surgically excised in part or who have fixed, invasive thyroid tumors, radiation therapy is recommended. Radiation treatment for thyroid tumors typically results in a sluggish, months-long response, and the majority of the time, tumor control is achieved. In some cases, radiation therapy can help thyroid cancers that were previously invasive become more receptive to surgery.
Another option is iodine therapy. Thyroid tumors can be treated by systemic administration of iodine-131; cats are the main species treated with this. There aren’t many places that can perform this, and there isn’t much information on how well it works with dogs.
Due to the increased risk of developing metastases, particularly in cases of bigger, bilateral, or invasive tumors, chemotherapy may be beneficial in dogs with thyroid tumors. A response rate of 30–50% has been recorded. With your oncologist, you can go over a number of strategies or possibilities for chemotherapy treatment of thyroid tumors.
Prognosis of Thyroid Cancer in Dogs
With the right treatment, dogs with thyroid cancers typically have an excellent prognosis. Malignant thyroid tumors in dogs have been reported to have an average survival duration of three months when left untreated.
Small, unilateral thyroid tumors in dogs are frequently surgically removed with reported median survival periods of more than 3 years.
According to one study, 25% of dogs with fixed thyroid tumors survive one year after surgery. There have been reports of median survival times of more than 2 years with radiation therapy. It’s interesting to note that dogs with lung metastases at diagnosis can nevertheless have long survival periods.