Sclerosing mucoepidermoid carcinoma with eosinophilia of the thyroid: more aggressive than previously reported

Sclerosing mucoepidermoid carcinoma with eosinophilia (SMECE) of the thyroid is a rare traditionally "low-grade" tumor that predominantly occurs in women. Approximately 50 cases have been reported in the literature. It arises in a background of Hashimoto thyroiditis and is characterized by nests of epidermoid and mucin-secreting cells located within an eosinophil-rich sclerotic stroma. Herein, we outline the clinicopathological and immunohistochemical characteristics of 6 cases of thyroid SMECE. All tumors were detected in women (age, 36-89 years; average, 59 years), and all patients underwent total thyroidectomies. Clinicopathological findings included extensive tumor invasion into the adjacent soft tissues, trachea, pharynx, and esophagus. Of 6 specimens, 5 had positive surgical margins. Cervical lymph node metastases were seen in 4, and distant metastases were in 3 patients. Immunohistochemically, all tumors were positive for CK19, galectin 3, and p63 and negative for calcitonin, calponin, S-100, and smooth muscle actin. Interestingly, 2 tumors also showed faint focal staining for thyroglobulin, and 2 others had focal positivity for thyroid transcription factor 1. Together, galectin 3 and CK19 expression supported the malignancy of these lesions, and p63 expression raised the possibility that these tumors originated from the ultimobranchial body. In summary, SMECE tumors in our series exhibit a clear female predominance with aggressive behavior and appear to arise from pluripotent solid cell nests. A correct diagnosis is crucial to providing SMECE patients with the appropriate treatment options, and we recommend a closer follow-up schedule than previously considered.