A rare case of intracytoplasmic mucin-rich nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus (EBV)-associated tumor with a high incidence in Asian countries. NPC is a type of squamous cell carcinoma originating from the nasopharyngeal mucosa. Although rare, NPCs show some uncommon histologic variants; these variations remain to be understood. We described the cytologic characteristics of a rare NPC variant with abundant intracytoplasmic mucin. A 37-year-old Japanese man presented to our hospital with bilateral ear discomfort and palpable lymph nodes. Nasopharyngeal biopsy showed tumor cells with abundant intracytoplasmic, Alcian blue-PAS-positive mucin. Immunohistochemical analysis demonstrated that the tumor cells were positive for p40 and p53. Epstein-Barr encoding region (EBER) in situ hybridization (ISH) showed EBV infection of the tumor cells. Fluorescence in situ hybridization (FISH) using MAML2 break-apart probes did not show split signals. Fine needle aspiration biopsy (FNAB) cytology of the metastatic lymph nodes was also performed. Smear samples had a necrotic and inflammatory background with both lymphocyte and neutrophil infiltration. Highly cellular tumor clusters and dispersed cells with naked nuclei were observed. The tumor cells showed a clear cytoplasm with distinct cell borders. Intracytoplasmic mucin pushing the nucleus to the periphery was observed in the scattered tumor cells in a liquid-based cytology sample. Given these findings, the final diagnosis was advanced nasopharyngeal carcinoma; cisplatin-based chemoradiation therapy was performed as the first-line treatment. The tumor recurred 8 months after completing the treatment. The recurrent nasopharyngeal tumor was a typical non-keratinizing NPC and lacked intracytoplasmic mucin.