Clinico-pathological Features and Outcome of Cats With Thyroid Carcinoma

Objectives: Thyroid carcinoma (TC) is an uncommon tumour in cats. The aims of this study were to describe the clinical presentation, response to treatment and outcome in a cohort of cats with thyroid carcinoma. Methods: This single-institute retrospective study reviewed medical records of cats histologically diagnosed with thyroid carcinoma between 2006 and 2023. Signalment, diagnostic tests, histopathological characteristics, treatment, and survival were evaluated. Results: Twenty-five cats were included. The most common presenting clinical signs were a palpable cervical mass, and weight loss. Nineteen cats (76%) received medical treatment for hyperthyroidism at the time of thyroid carcinoma diagnosis, with 14 (74%) demonstrating persistently elevated total thyroxine levels. Twenty-three cats (92%) underwent curative-intent treatment including: thyroidectomy (n = 13), thyroidectomy followed by high-dose radioiodine (HD-RAI) (n = 9) and HD-RAI as single modality (n = 1). Hyperthyroidism resolved in 17 out of 22 cats (77%) after treatment. Follicular carcinoma was the most common histopathologic subtype (n = 10) followed by papillary (n = 2). Metastasis was present in 12 cats (48%); confirmed in 10 cats either by cytology or histopathology and suspected in two cats based on scintigraphy. Median tumour-specific survival for cats receiving curative-intent treatment was not reached, and when all-cause mortality was considered, median overall survival time was 795 days (95% CI 503–1086). No variable was associated with survival in cats receiving curative-intent treatment. Conclusions: Cats diagnosed with TC can experience prolonged survivals and normalisation of thyroxine levels when receiving curative-intent treatment. Metastatic rate was moderate but did not impact outcome.