Poorly differentiated mucoepidermoid carcinoma of the thyroid.

Mucoepidermoid carcinomas (MECs) are the most common malignant tumour of the salivary glands. MECs have also been reported to occur in atypical sites. Primary MECs of the thyroid gland are extremely rare, accounting for 0.5% of thyroid malignancies with approximately 48 cases reported in the literature. In most cases, these are low-grade neoplasms with good long-term prognosis. We present the case of a 74-year-old patient with poorly differentiated MEC of the thyroid gland, which behaved aggressively resulting in rapid decline and death of the patient. The exact pathophysiology of the disease remains unclear and there is no consensus on the optimal treatment for this histological subtype. Recognition and diagnosis of this rare neoplasm are important as this can help guide optimal treatment, although in high-grade poorly differentiated cases, treatment options remain limited. © BMJ Publishing Group Limited 2020. No commercial re-use. See rights and permissions. Published by BMJ.