Nasopharyngeal carcinoma.

Nasopharyngeal carcinoma represents a morphologic spectrum of neoplasms localized to the nasopharynx and arising from nasopharyngeal epithelium. Nasopharyngeal carcinomas have rather unique clinical, epidemiologic, pathologic, and biologic features. The morphologic spectrum of nasopharyngeal carcinoma includes keratinizing, nonkeratinizing, and undifferentiated subtypes. The separation of these morphologic types is not an academic exercise, but has practical importance relative to differential diagnosis, management, and prognosis. A similar morphologic classification applies to carcinomas arising in the palatine tonsils and the base of tongue. The nasopharynx, palatine tonsils, and base of tongue are collectively designated as Waldeyer's tonsillar tissues. Awareness of the morphologic spectrum of Waldeyer's ring carcinomas may assist in suggesting the primary tumor site in the face of an occult metastatic carcinoma to cervical neck lymph nodes.