Thyroid-Like Low-Grade Nasopharyngeal Papillary Adenocarcinoma

OBJECTIVES: Thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TLLGNPPA) is a relatively rare nasopharyngeal tumor. We performed morphological characterization, immunohistochemical profiling, and investigated gene mutations. We also provide clinical follow-up data and brief review of the literature. METHODS: Immunohistochemistry was used to evaluate the expression of TTF-1, CK19, CK7, EMA, TG, Pax-8, CK5/6, S100, and Ki-67. Additionally, in situ hybridization was utilized to identify the presence of EBV. We investigated mutations in hot-spot exons of KRAS/NRAS/BRAF to rule out common mutations seen in thyroid tumors. RESULTS: Histopathologic examination of four cases identified tumors that were mainly occupied by papillary architectures. One case had a predominantly glandular structure. The tumors expressed TTF-1 and CK19, while TG and Pax-8 were negative. S100 was moderately expressed focally in three cases. CONCLUSIONS: While TLLGNPPA displays a morphological resemblance to papillary thyroid carcinoma (PTC), it is vital to differentiate nasopharyngeal metastasis from PTC for appropriate treatment.