Morphologic features of conventional squamous cell carcinoma of the oropharynx: 'keratinizing' and 'nonkeratinizing' histologic types as the basis for a consistent classification system.

Morphologic assessment is one of the most basic tools that pathologists use to classify tumors. Human papillomavirus (HPV)-related squamous cell carcinoma of the oropharynx has unique morphologic features that can be readily recognized under the microscope. Yet, these features are not widely recognized or uniformly reported. In our practice, we group oropharyngeal squamous cell carcinomas into 'nonkeratinizing', 'nonkeratinizing with maturation', and 'keratinizing' histologic types. The 'nonkeratinizing' type has a very strong association with HPV, while the 'keratinizing' type has a weaker association with the virus. 'Nonkeratinizing with maturation' is intermediate but much more closely related to the 'nonkeratinizing' type. This classification system parallels that of sinonasal and nasopharyngeal squamous cell carcinomas where nonkeratinizing squamous cell carcinomas are widely recognized histologic variants. This review will discuss this classification system and its utility in routine clinical practice.