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Introduction:In the past several decades,declining incidences of nasopharyngeal carcinoma(NPC) have been observed in Chinese populations in Hong Kong,Taiwan,Los Angeles,and Singapore.A previous study indicated that the incidence of NPC in Sihui County,South China remained stable until 2002,but whether age,diagnosis period,and birth cohort affect the incidence of NPC remains unknown.Methods:Age-standardized rates(ASRs) of NPC incidence based on the world standard population were examined in both males and females in Sihui County from 1987 to 2011.Joinpoint regression analysis was conducted to quantify the changes in incidence trends.A Poisson regression age-period-cohort model was used to assess the effects of age,diagnosis period,and birth cohort on the risk of NPC.Results:The ASRs of NPC incidence during the study period were 30.29/100,000 for males and 13.09/100,000 for females.The incidence of NPC remained stable at a non-significant average annual percent change of 0.2%for males and-1.6%for females throughout the entire period.A significantly increased estimated annual percent change of 6.8%(95%confidence interval,0.1%-14.0%) was observed from 2003 to 2009 for males.The relative risk of NPC increased with advancing age up to 50-59 and decreased at ages >60 years.The period effect curves on NPC were nearly flat for males and females.The birth cohort effect curve for males showed an increase from the1922 cohort to the 1957 cohort and a decrease thereafter.In females,there was an undulating increase in the relative risk from the 1922 cohort to the 1972 cohort.Conclusions:The incidence trends for NPC remained generally stable in Sihui from 1987 to 2011,with an increase from 2003 to 2009.The relative risks of NPC increased in younger females.