**3.3 Pathological classification**

Histologically, NPC cells are regarded to be squamous in origin, but with a high background of lymphoid cells. According to the world health organization (WHO), NPC was categorized into three types: nonkeratinizing carcinoma, keratinizing squamous cell carcinoma, and basaloid squamous cell carcinoma [33]. In the endemic areas, over 95% of the cases belong to the nonkeratinizing type, while less than 5% belong to the keratinizing squamous cell carcinoma type, and basaloid squamous cell carcinoma type is extremely rare. On the contrary, in nonendemic western countries like the United States, keratinizing squamous cell carcinoma accounts for more than 25% of NPC cases [34, 35].
