Feline thyroid carcinoma: diagnosis and response to high-dose radioactive iodine treatment.

This study reports the scintigraphy, histopathology, sole treatment with high-dose radioactive iodine and outcome of eight cases of feline thyroid carcinoma. Scintigraphic findings were variable and in 7/8 cases scintigraphic features could not reliably distinguish whether the thyroid tissue was malignant. Histopathology revealed typical criteria of malignancy in all cases, with mitotic activity described most frequently (7/8 cases), followed by infiltration of local tissues (4/8 cases). Cellular pleomorphism was infrequently observed. Single high-dose (1100MBq I(131)) radioiodine therapy was successful in 6/8 cases, with complete resolution of hyperthyroidism, and was associated with prolonged survival times (181-2381 days). Sole treatment with high-dose radioiodine is a safe and effective treatment for functional thyroid carcinoma. The prognosis for feline thyroid carcinoma successfully treated with radioiodine is good, with extended survival times commonly achieved.