Clinico-pathological features and outcome of cats with thyroid carcinoma

Thyroid carcinoma 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. 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. 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. Cats diagnosed with thyroid carcinoma can experience prolonged survivals and normalisation of thyroxine levels when receiving curative-intent treatment. Metastatic rate was moderate but did not impact outcome.