Treatment of Differentiated Thyroid Carcinoma in 7 Dogs Utilizing131i

Seven dogs with thyroid gland carcinoma were treated with131I and hormone suppressive therapy either alone (3 dogs) or in combination with surgery (3 dogs) or137Cs teletherapy and chemotherapy (1 dog). Empirically chosen doses of 75 to 137 mCi of131I were given orally (2 dogs) and intravenously (5 dogs). Adverse effects were limited to acute, transient bone marrow hypoplasia and pancytopenia. Nominal objective reduction in tumor volume or size and number of pulmonary metastases was observed in 4 dogs treated with131I and thyroxine. Of these 4 dogs, 2 had stable disease for periods of 4 and 12 months while a third dog had stable disease for 27 months following two131I treatments at 3 month intervals. The fourth dog had progressive disease. Two dogs with mediastinal metastases showed reduction in localization of99mTc pertechnetate and radioiodine following 2 and 3 treatments using131I. It appears that relatively high doses of131I can be used safely for the treatment of canine thyroid tumors and that further investigation can be justified to define its efficacy.