PRIMARY MUCOEPIDERMOID CARCINOMA OF THE THYROID-GLAND - A REPORT OF 6CASES AND A REVIEW OF THE LITERATURE OF A FOLLICULAR EPITHELIAL-DERIVED TUMOR

Primary mucoepidermoid carcinomas of the thyroid gland are uncommon tu mors of low-grade malignant potential. We report six cases of thyroid mucoepidermoid carcinoma, four occurred in women and two in men with a n age range of 29 to 57 (median, 46 years). The clinical presentation was that of a painless mass. Radiographic studies showed a single, sol id, ''cold'' nodule in either the right or left lobe, or isolated to t he isthmus, There was no history of a mucoepidermoid carcinoma develop ing in more typical locations (eg, salivary gland) in any of the patie nts. Histologically, the tumors were characterized by an intimate admi xture of squamoid/epidermoid cells and mucocytes, The tumors were deli neated but not encapsulated with prominent cyst formation and a variab le amount of associated fibrosis. The squamoid component showed horny pearl formation, individual cell keratinization and/or the presence of intercellular bridges, Intracytoplasmic and luminal epithelial mucin was observed in all cases, In three of the cases a prominent eosinophi lic cellular infiltrate was intimately identified within the neoplasti c proliferation. One other case was noteworthy for the presence of cil iated epithelium. In all of the cases the uninvolved thyroid tissue sh owed the presence of lymphocytic thyroiditis. Rare foci of squamous me taplasia were observed in two of the cases. A microscopic focus of thy roid papillary carcinoma was observed adjacent to the mucoepidermoid c arcinoma in one case, Immunohistochemical evaluation of the mucoepider moid carcinoma showed the following antigenic profile: cytokeratin (fi ve of five), CAM 5.2 (four of four), thyroglobulin (five of six), calc itonin (none of six), chromogranin (none of six), polyclonal carcinoem bryonic antigen (four of four), and monoclonal carcinoembryonic antige n (none of five). Surgical excision was the treatment of choice, All o f the patients reported are alive without disease (recurrence or metas tasis) over periods ranging from 1 to 15 years. Based on our findings, we believe that these tumors are of low-grade malignant potential and originate from thyroid follicular epithelial cells rather than from s olid cell nests of the ultimobranchial body.