Mucinous Variant of Follicular Carcinoma of the Thyroid Gland: Case Report and Review of the Literature

The rare reports of mucinous variant of follicular carcinoma of the thyroid gland have not provided enough evidence to support the recognition of these tumors as a distinct clinicopathologic entity or to understand their etiopathogenesis. We report the fourth case of mucinous variant of follicular carcinoma displaying a minimally invasive tumor with diffuse expression of thyroglobulin, TTF-1, CD56, PAX-8, cytokeratins 7 and 19, in the absence of monoclonal carcinoembryonic antigen (CEA), cytokeratin 20, chromogranin, HBME-1, P63 expression, and BRAF gene mutation, in a 51-year-old woman who is alive without signs of disease 13 months after total thyroidectomy, bilateral neck dissection, and radioactive iodine. Herein, fine-needle aspiration cytology disclosed worrisome cytologic features consisting of large epithelial cells arranged in clusters or singularly, with high nucleocytoplasmic ratio, nuclear grooves and evident nucleoli which were shared by those of mucin-producing papillary thyroid carcinoma. Therefore, knowledge of the cytological and histopathological spectrum of this lesion is important to avoid misdiagnosis. The morphologic clues leading to the correct diagnosis of mucinous variant of follicular neoplasm have been correlated with the data of the literature, and the differential diagnosis is briefly discussed.