What is Thyroid Cancer in Dogs?
Thyroid cancer in dogs affects the thyroid gland, situated in the neck with two lobes on each side of the trachea. This gland plays a crucial role in regulating the body’s metabolism by producing thyroid hormone. Tumors in the thyroid gland can be categorized as benign (non-cancerous) or malignant (cancerous).
Malignant tumors in the thyroid can impact one or both lobes, and they possess the potential to metastasize to other parts of the body. Occasionally, dogs may have thyroid tissue located elsewhere in the body, known as ectopic thyroid tissue, which is susceptible to cancer development. Ectopic thyroid tissue, though rare, is commonly found at the base of the tongue.
Thyroid cancer is characterized by local invasiveness, indicating its ability to grow within a specific area, along with the potential for metastasis to other organs. Common sites for local invasion include the trachea and esophagus, while metastasis typically involves the lymph nodes followed by the lungs. By the time of diagnosis, these tumors often have already spread.
Benign thyroid tumors, referred to as adenomas, do not spread and generally do not affect the long-term health of dogs. However, such tumors are uncommon, as approximately 90 percent of thyroid tumors in dogs are malignant. Malignant thyroid tumors, known as carcinomas, originate from epithelial tissue, specifically from the thyroid gland.
Symptoms
Thyroid cancer in dogs can often manifest without noticeable symptoms. However, in many cases, the presence of a mass can be detected by running your hands along the underside of the neck. As the condition progresses, the thyroid tumor may begin to invade nearby tissues such as the trachea, resulting in symptoms like coughing, difficulty exercising, and alterations in breathing patterns. If the esophagus is affected, common signs may include difficulty swallowing or eating.
Other general symptoms observed in dogs with thyroid cancer include weight loss, decreased appetite, changes in vocalization (such as barking), and lethargy.
Causes
The causes of thyroid cancer in dogs, much like in humans, remain largely unknown. It is believed to be a complex process influenced by various factors, including breed, sex, genetic predisposition, and environmental factors.
Certain breeds are more commonly diagnosed with thyroid cancer, including Golden Retrievers, Beagles, Boxers, and Huskies. These breeds are overrepresented in thyroid cancer diagnoses, suggesting a potential genetic or breed-specific predisposition to the condition.
Diagnosis
The diagnosis of thyroid cancer in dogs typically begins with a comprehensive assessment, similar to other medical conditions. Veterinarians may suggest the following non-invasive tests for diagnosis:
- A physical examination to detect the presence of a mass.
- Blood tests to identify any abnormalities in white cell counts or organ function.
- Chest X-rays to assess for metastasis or the spread of the disease.
- Ultrasound of the neck to determine the size of the tumor and assess lymph node enlargement.
In cases where a thyroid tumor is suspected, veterinarians may recommend a CT or MRI scan before surgery to evaluate the extent of the disease. These imaging procedures require anesthesia and thorough planning, often taking several hours to complete. A surgical biopsy is usually necessary to obtain a definitive diagnosis.
Treatment
Treatment options for thyroid cancer in dogs vary based on the type and extent of the tumor. Common approaches for managing canine thyroid cancers include:
- Surgery
- Chemotherapy
- Radiation therapy
For dogs with thyroid tumors that have minimal invasion into surrounding tissues, surgery is often the recommended course of action. This procedure, known as a thyroidectomy, involves the physical removal of the tumor, followed by a biopsy to determine whether the cancer is benign or malignant.
Depending on the extent of tumor removal during surgery, additional treatment such as chemotherapy or radiation therapy may be advised. Both radiation and chemotherapy involve multiple sessions over several weeks, with the specific treatment regimen tailored to the individual case.
In cases where surgery is not feasible, either due to the size of the tumor or underlying health conditions that increase the risk of anesthesia, radioactive iodine (I-131) therapy may be considered. This treatment involves injecting radioactive iodine into the patient to target and destroy active cancerous tissue. While commonly used in cats, its application in dogs may be limited due to factors such as cost and availability of large doses.
Recovery and Management
After thyroidectomies, most dogs recover well post-operatively with minimal complications, although there are inherent risks associated with any surgical procedure requiring anesthesia. Recovery may necessitate overnight monitoring in the hospital, with discharge typically occurring the next day in the majority of cases.
Prognosis and life expectancy are influenced by factors such as the size and extent of tumor spread. Dogs with completely surgically removed thyroid tumors may have a median survival time exceeding two years. In cases where tumors necessitate follow-up treatment with chemotherapy and/or radiation, prognosis remains favorable, with a median survival time ranging from 18 to 24 months.
However, for dogs undergoing radiation and chemotherapy without surgical intervention, prognosis is less promising, with an average survival time typically falling between 6 and 12 months, contingent upon the extent of metastasis.
Thyroid Cancer in Dogs FAQs
What is the speed of thyroid cancer spread in dogs?
Thyroid cancer spreads rapidly in dogs, with approximately 35 percent of them already experiencing metastasis upon diagnosis.
What is the life expectancy of dogs diagnosed with thyroid cancer?
The life expectancy of dogs diagnosed with thyroid cancer varies, typically ranging from six months to two years, depending on the treatment methods employed.