Prolonged survival in 58 dogs with thyroid carcinoma treated with radioactive iodine as sole therapy
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Treatment of thyroid carcinomas in people and dogs often involves multimodal therapy, including radioactive iodine (I-131). The objective of this study is to describe outcomes associated with I-131 as sole therapy in dogs with thyroid carcinoma. Retrospective review of medical records from a single institution (2004-2021) of dogs treated with intravenous I-131 was performed. Dogs were included if they had macroscopic thyroid carcinoma, received I-131 as a sole treatment and follow up information was available. Fifty-eight client owned dogs met inclusion criteria. 10/58 (17 percent) had non-neck tumor location. 21/52 (40 percent) dogs with known thyroid status were hyperthyroid prior to treatment. 16/51 (28 percent) of dogs had stage IV disease. Maximal responses were recorded in 49 (84 percent) of dogs; of these, objective responses were available in 20 (41 percent) and subjective responses were available in 29 (59 percent) of dogs. The overall response rate of dogs with recorded responses was 65 percent including 8 (16 percent) of dogs achieving a complete remission and 24 (49 percent) of dogs achieving a partial response (PR). Stable disease (SD) was documented in 14 (28 percent) of the population and progressive disease was noted in 3 (6 percent) of dogs. Hyperthyroidism resolved in all dogs. Of 50 evaluable dogs, 30 (60 percent) progressed. The median progression free interval (PFI) was estimated to be 614 days (range 30-2213). The median survival time (MST) was estimated to be 629 days (range 30-2213); 7 dogs were alive and censored. Dogs with distant metastasis (stage IV) at the time of diagnosis had significantly shorter MST (385 days) when compared to dogs of lower stage (p = 0.0021). No survival difference was identified based on thyroid hormone status or tumor location. Minimal toxicity was observed. This cohort uniquely demonstrates the value of I-131 as a sole therapy in dogs with thyroid carcinoma. Despite advanced disease in many cases, PFI and MST were prolonged.
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M.S.