Mucoepidermoid carcinoma of the thyroid

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Abstract
Clinical and morphological features of 3 cases of primary mucoepidermoid carcinoma of the thyroid are described. The tumors were composed of 2 cell types. One of these resembled squamous epithelium and ultrastructurally showed tonofilaments and numerous desmosomes. The other cell type contained Alcian blue and mucicarmine positive mucin and, on EM showed mucigen granules. Marked stromal fibrosis and psammoma bodies were seen in all tumors. Immunohistochemical studies showed that the tumor cells were negative for thyroglobulin. A few calcitonin-containing cells were seen in 1 metastatic tumor. One tumor showed, in addition to the histological features of mucoepidermoid carcinoma, anaplastic areas with obvious transition between the 2 histological patterns. The same thyroid also had a small thyroglobulin-positive papillary carcinoma in the opposite lobe. All tumors presented lymph node metastases. In 2 cases the primary tumor was confined within the thyroid capsule but that with anaplastic areas invaded surrounding structures. This patient died 13 mo. after diagnosis; the other patients are alive and symptomless 1 and 10 yr since diagnosis. Mucoepidermoid carcinoma of the thyroid appears to be a clinicopathological entity that resembles papillary carcinoma in its natural history. The origin of the tumor is unclear. The tumor might be related to the ultimobranchial system although some histological features also appear to favor a common origin with papillary carcinoma.