TREATMENT OF DIFFERENTIATED THYROID-CARCINOMA IN 7 DOGS UTILIZING I-131

Seven dogs with thyroid gland carcinoma were treated with I-131 and hormone suppressive therapy either alone (3 dogs) or in combination with surgery (3 dogs) or Cs-137 teletherapy and chemotherapy (1 dog). Empirically chosen doses of 75 to 137 mCi of I-131 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 with I-131 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 two I-131 treatments at 3 month intervals. The fourth dog had progressive disease. Two dogs with mediastinal metastases showed reduction in localization of Tc-99m-pertechnetate and radioiodine following 2 and 3 treatments using I-131. It appears that relatively high doses of I-131 can be used safely for the treatment of canine thyroid tumors and that further investigation can be justified to define its efficacy.