Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma: case report and literature review.

Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TL-LGNPPA) is an extremely rare neoplasm characterized by morphological analogy to papillary thyroid carcinoma and abnormal expression of thyroid transcription factor-1 (TTF-1). Here we report a novel case of TL-LGNPPA with literature review. The patient was a 43-year-old woman complaining of nasal obstruction. Laryngoscopic study and computed tomography identified a pedunculated mass located on the posterior edge of the left nasal septum. Histologically, the tumor consisted of papillary growth of cuboidal or columnar epithelium. Tubular architecture and a spindle cell component were also observed focally. Some tumor cells exhibited intra-nuclear cytoplasmic inclusions. Immunohistochemically, the neoplastic cells were positive for pancytokeratin (AE1/AE3), CK7, CK19, TTF-1, vimentin and HBME1, but negative for thyroglobulin, Pax8 and CK5/6. Ki67-labeling index reached 5% in the most concentrated spot. Despite the morphological and immunohistochemical similarity to papillary thyroid carcinoma, no BRAF V600E mutation was detected by mutation-specific immunohistochemistry. The patient had neither local recurrence nor distant metastasis 19 months after removal of the tumor.