Solid cell nests of the thyroid gland: precursor of mucoepidermoid carcinoma?

Solid cell nests (SCN) are found within the thyroid parenchyma on routine clinical pathological examinations, but their histogenesis and clinical significance are still obscure. From November 1987 to May 1991, a total of 3,260 patients underwent thyroid surgery at Ito Hospital and SCN were noted in 42 (1.3%) patients. Serial sections of the specimens from these patients were studied morphologically and immunohistochemically. The location and growth pattern of SCN within the thyroid parenchyma were distinct from those of hyperplastic C-cells. SCN were located in the isthmus lobe in 1 patient and even in the pyramidal lobe in 3 patients. In another patient neoplastic proliferation of SCN was observed. Immunohistochemically, SCN were negative for neuron-specific enolase, chromogranin A, and S-100 protein. These findings strongly suggest that SCN are of endodermal origin and that they may be closely related to mucoepidermoid carcinoma of the thyroid gland.