Difference in the incidence trend of nasopharyngeal and oropharyngeal carcinomas in Taiwan: implication from age-period-cohort analysis.

Lifestyle factors are considered important for the pathogenesis of both nasopharyngeal and oropharyngeal carcinomas. In Taiwan, the incidence of nasopharyngeal carcinoma gradually decreased over the past 20 years, whereas that of oropharyngeal carcinoma increased rapidly. To compare the incidence trends of nasopharyngeal and oropharyngeal carcinomas in Taiwan, the age-period-cohort model was used to analyze epidemiologic data from 1981 to 2000 obtained from the Taiwan Cancer Registry. The calendar time period of 1986 to 1990 and the 1931 to 1940 birth cohort were used as reference groups for estimates of relative risk. For nasopharyngeal carcinoma, the incidence seemed to decrease in most age groups and was more prominent in women (30%) than in men (23%). For oropharyngeal carcinoma, the incidence increased in all age groups and was more prominent in men (391.4%) than in women (59.2%). Cohort effect was found for both nasopharyngeal and oropharyngeal carcinomas. The relative risk of nasopharyngeal carcinoma for the 1971 to 1980 birth cohort was 0.38 for women and 0.68 for men. The relative risk of oropharyngeal carcinoma for the 1971 to 1980 cohort was 45.67 for men and 2.69 for women. Change in lifestyle seemed to be an important factor for the difference in the incidence trend between nasopharyngeal and oropharyngeal carcinomas and between men and women.