Histopathological types of nasopharyngeal carcinoma in a low-risk area: Japan.

NPC in Japan was studied histopathologically by examining 816 NPCs from among 3 338 biopsies from patients with tumours of the nasopharynx and other parts of the upper respiratory system. In addition, a comparative study on NPC among Taiwanese and an immunoserological study were carried out. When comparing histological types of malignant tumours of the upper respiratory tract, poorly-differentiated squamous-cell carcinoma predominated only in those of the nasopharynx. Malignant nasopharyngeal tumours in Japanese patients were characterized by two histological features: predominance of squamous-cell carcinoma, especially of the poorly-differentiated type, and a relatively high frequenty of malignant lymphoma. An analysis of 731 cases of NPC showed that a vast majority (86.7%) were poorly-differentiated and a minority (13.3%) well-differentiated squamous-cell carcinomas. The former included 45.8% spindle-polygonal-cell carcinomas, 26.6% transitional-cell carcinomas ana 14.3% lymphoepitheliomas. Although the transitional-cell carcinomas and lymphoepitheliomas showed a peculiar morphology, it was confirmed that they are of a squamous nature. A comparative study of the histology of NPCs in a high-risk area, Taiwan, and in a low-risk area, Japan, revealed considerable differences between the two groups. Well-differentiated carcinomas were infrequent in both groups but were more frequent in Japanese than in Taiwanese, while the frequency of poorly-differentiated carcinomas, especially transitional-cell carcinomas and lymphoepitheliomas, was much higher among Taiwanese. A seroepidemiological study on the relation of anti-VCA antibody titres to histological type of tumour in 84 Japanese NPC patients revealed that the rate of positivity and the geometric mean of the titres were considerably higher in patients with lymphoepitheliomas. Althougropathological study along this line would appear to be important, since the results obtained in Japanese NPC cases may suggest that EBV genomes in NPC cells vary with the grade of differentiation of NPC.