The treatment choice depends on the size of the tumor, its distribution towards other tissues, the presence of metastases and whether there are symptoms present of a disturbed thyroid function.
Surgery is advised when the tumor is not attached onto the surrounding tissues (which is the case in 25-50% of thyroid tumors) and there are no metastases. Risks linked to surgery are possible bleedings, accidentally removing the nearby parathyroid glands (causing a disturbance of the calcium metabolism), larynx nerve damage and a too low thyroid function when both thyroid lobes have to be removed.
Radiation is often used after surgery when residual tumor tissue is suspected or when surgery is not a good option (e.g. when the tumor is fused to the environment). Possible side effects of radiation consist of damage to the larynx, trachea and esophagus, although in general, radiation is well tolerated. It is possible that after a while (months to years after treatment) insufficient thyroid hormones are produced. On the other hand, these hormones can be supplemented.
Radioactive iodine therapy
if the tumor takes up iodine well, radioactive iodine therapy is an interesting treatment option. Radioactive iodine is administered to the dog and will build up in the thyroid tissue. There, it locally radiates the thyroid tissue, including the tumor. Depending on the amount of thyroid tissue that gets destroyed, it might be necessary to supplement thyroid hormones after the treatment. The advantage of this treatment option vs radiation is that through radioactive iodine both the metastases of the thyroid tumor as the thyroid tumor itself can be very precisely treated, at least if both take up iodine. Moreover, if necessary, the treatment can be repeated without much side effects.
Chemotherapy can be considered for dog with large, non-resectable tumors or many metastases, although the results for chemotherapy are thus far not as good as for the treatments mentioned above. In some dogs with tumor type good results were obtained (up to a year survival), but at this point it is unclear which dogs benefit from this.