Extensive mucoepidermoid carcinoma-like differentiation in follicular carcinoma of the thyroid

Mucoepidermoid carcinoma (MEC) is a rare malignant thyroid neoplasm. Cases of MEC with papillary, insular, and anaplastic thyroid carcinoma have been reported. Here, we present a case of follicular carcinoma with extensive MEC-like differentiation. A 62-year-old female presented with complaint of thyroid swelling for 10 years. Cytological features were suggestive of follicular neoplasm. Contrast-enhanced computed tomography showed metastasis to lung and vertebrae. Salivary glands and breasts were normal on examination and imaging. Subtotal thyroidectomy with bilateral neck dissection surgery was performed. The specimen was submitted for histopathological examination. Microscopy showed features of follicular carcinoma with capsular and vascular invasion along with an additional MEC-like morphology. Follicular carcinoma with extensive MEC-like differentiation is a rare observation. Since the tumor was sparing salivary glands and breasts, we considered it as mucoepidermoid differentiation over a collision tumor. However, immunohistochemistry and molecular analysis were the limitations.