Thyroid cancer
Diagnosis
The diagnosis of thyroid cancer in dogs consists of several steps: the anamnesis, physical examination, cytology, blood tests (including thyroid function), medical imaging of the neck, chest and abdomen (chest radiographs and abdominal ultrasound, full body CT scan), histological and immunohistochemical examination of the thyroid tissue and scintigraphic examination of the thyroid gland to determine whether radioactive iodine-131 is an appropriate treatment option. Each step in the diagnosis is important to confirm the diagnosis of thyroid cancer, to know the type of thyroid cancer and to determine the most appropriate treatment plan.
General info
The thyroid gland in dogs consists of 2 lobes and is located in the neck. The healthy thyroid gland cannot be felt. The thyroid is one of the few organs in the body that is able to actively absorb iodine from the bloodstream. In the case of thyroid cancer in the dog, an enlarged palpable swelling in the neck is usually the first thing to be seen. Other common complaints are coughing and difficulty breathing due to pressure from the swelling on the trachea. Thyroid cancer in dogs is in many cases malignant (thyroid carcinoma). The malignant character is characterized by the ingrowth of the swelling into the surrounding tissue as well as by the presence of metastases in other organs. Therefore, early diagnosis and proper treatment are of great importance in managing thyroid cancer in dogs.
CT scan of the dog's neck (cross section): right thyroid cancer.
Therapy
Several treatment options for canine thyroid cancer are known, each with varying degrees of success: surgical removal of the swelling, radioactive iodine-131, radiotherapy, chemotherapy and drug therapy. The choice of treatment mainly depends on the malignancy of the cancer (ingrowth into surrounding tissue, presence of metastases), type of thyroid cancer as well as the possibility of uptake of (radioactive) iodine. Despite the range of treatment options, there is still much room for improvement in the treatment of thyroid cancer in dogs. For example, there is no (ideal) treatment option for those dogs with thyroid cancer that has grown into the surrounding tissue and/or the presence of metastases and that is insensitive to radioactive iodine-131. Further research is needed to provide this group of dogs with a good quality of life. In addition, the successful radioactive iodine-131 therapy has some drawbacks: on the one hand, half of all thyroid cancers lose the ability to absorb (radioactive) iodine, on the other hand, a high amount of radioactive iodine is needed in the treatment of thyroid cancer in dogs. The latter is associated with a high level of radioactivity for the dog as well as its environment (including owner and veterinarian). Despite the good results with radioactive iodine-131 therapy, an optimization of this treatment is required.