Abstract
In humans, recombinant human thyrotropin (rhTSH) enhances radioactive iodine uptake (RAIU) in patients with differentiated thyroid cancer. No studies have been performed in veterinary medicine to optimize radioiodine treatment of thyroid cancer. The aim of this study was to evaluate the effect of rhTSH on the uptake of radioiodine-123 (123I) in dogs with thyroid tumors. Nine dogs with thyroid neoplasia were included in this prospective cross-over study. The dogs were divided in 2 groups. In one group, 123I was administered for a baseline RAIU determination in week 1. In week 2 (after a washout period of 2 weeks), these dogs received rhTSH (100 μg IV) 24 h before 123I injection. In the other group the order of the protocol was reversed. For each scan, the dogs received 37 MBq (1 mCi) of 123I intravenously (IV) and planar scintigraphy was performed after 8 and 24 h for tumor RAIU calculation. Overall, rhTSH administration caused no statistically significant change on thyroid tumor RAIU at 8 h (p = 0.89) or at 24 h (p = 0.98). A significant positive correlation was found between the effect of rhTSH on tumor 8h-RAIU and rhTSH serum concentrations at 6 h (τ = 0.68; p = 0.03), at 12 h (τ = 0.68; p = 0.03) and at 24 h (τ = 0.78; p = 0.02) after rhTSH injection. This study suggests that IV administration of 100 μg rhTSH 24 h before 123I has an inconsistent effect on thyroid tumor RAIU. Further studies are necessary to determine the best protocol of rhTSH administration to optimize thyroid tumor RAIU.
Highlights
Thyroid tumors account for 10–15% of all head and neck neoplasms in dogs [1,2]
The goal of this study was to evaluate the effect of 100 mg rhTSH, administered IV 24 h before 123I, on tumor radioactive iodine uptake (RAIU) in dogs with thyroid tumors
Six dogs were diagnosed with unilateral thyroid tumors, 1 dog had bilateral thyroid tumors and 2 dogs had ectopic tumors
Summary
Thyroid tumors account for 10–15% of all head and neck neoplasms in dogs [1,2]. Ninety percent of canine thyroid tumors are carcinomas and 16–38% of the patients present evidence of metastasis at the time of diagnosis [1,3]. Surgery is the preferred treatment modality for mobile tumors, while large invasive tumors have a better prognosis with external beam radiation or radioactive iodine-131 (131I) therapy [1]. High doses of 131I are required and this usually implies a prolonged hospitalization period and high doses of radiation eliminated to the environment through the excreta. Major limitations of 131I therapy include its selected effectiveness in differentiated thyroid tumors exhibiting adequate 131I uptake and the potential need of multiple treatments for tumor control
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