Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma: report of two cases.

Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (LGNPPA) is extremely rare; only four cases have been reported. Herein are presented the case reports of two Japanese male patients with thyroid-like LGNPPA. Macroscopically, these tumors were pedunculated polypoid masses on the roof of the nasopharynx. Microscopically, they were characterized by papillary and glandular epithelial proliferation. The papillae were complex and tightly packed with hyalinized fibrovascular cores and lined by columnar and pseudostratified cells with intervening spindle-shaped cells. Both cell types had round to oval vesicular nuclei with tiny nucleoli and mildly eosinophilic cytoplasm. Mitotic figures were not evident and necrosis was not observed. Psammoma bodies were seen focally in one of the patients. Transition from normal surface epithelium to tumor cells was identified in both cases. On immunohistochemistry the tumor cells were positive for cytokeratin (CK)7, CK19, thyroid transcription factor-1 (TTF-1) and vimentin. They were negative for CK5/6, CK20, thyroglobulin, S-100 protein and CD15. In situ hybridization for EBV was negative. Nasopharyngeal tumors with similar morphological appearance should be examined for TTF-1 immunoreactivity, and patients should be clinically followed to determine the course of this unusual disease and the significance of TTF-1 expression.