Composite Mucoepidermoid Carcinoma and Columnar Cell Variant of Papillary Carcinoma of the Thyroid

Primary mucoepidermoid carcinoma (MEC) of the thyroid and columnar cell variant of papillary carcinoma of the thyroid (PCT) are uncommon neoplasms. We report the first case of composite MEC and columnar cell variant of PCT. An 86-year-old man consulted for a 47-mm thyroid nodule, cytologically compatible with PCT. Total thyroidectomy was performed. Histological diagnosis, with support of histochemistry and immunohistochemistry, was mixed primary carcinoma of the thyroid, associating an MEC component with predominantly columnar cell variant of PCT. Sixteen months after surgery and external beam radiation therapy, the patient was free of recurrence or distant metastasis. This case report offers an opportunity to highlight the potential pitfalls concerning the interpretation of mucin histochemistry in thyroid tumors.