Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma: A case report.

Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TL-LGNPPA) is a rare neoplasm characterized by morphological analogy to papillary thyroid carcinoma and abnormal expression of thyroid transcription factor-1 (TTF-1). We herein report a rare case of TL-LGNPPA with a review of its clinical, morphological and immunohistochemical characteristics. The patient was a 25-year-old Japanese woman complaining of a 2-year history of fever of unknown origin. There were no remarkable physical findings and the laboratory tests, including C-reactive protein levels, were normal. Laryngoscopy, magnetic resonance imaging and fluorodeoxyglucose-positron emission tomography identified a pedunculated mass at the roof of the nasopharynx. Histologically, the tumour exhibited papillary growth of cuboidal or columnar epithelium. Tubular architecture and a spindle cell component were also observed focally. Some tumour cells exhibited intranuclear cytoplasmic inclusions. Immunohistochemically, the neoplastic cells were positive for TTF-1, cytokeratin 7 and vimentin, but were negative for thyroglobulin. The Ki-67 labelling index (MIB-1 index) reached 5% in the most concentrated spot. The patient had neither local recurrence nor distant metastasis 3 years after removal of the tumour. In conclusion, TL-LGNPPA should be included it in the differential diagnosis of fever of unknown origin.