Age-incidence relationships and time trends in cervical cancer in Sweden.

Age-incidence relationships are informative of carcinogenic mechanisms. These have been previously assessed for cervical squamous cell carcinoma (SCC) but not for adenocarcinoma. The aim was to assess by means of age-, period- and cohort-specific analyses and Poisson regression modelling whether the two types of cervical cancer show an age-incidence maximum at a relatively young age, as shown in cross-sectional analyses. The Swedish Family-Cancer Database was used to analyse age-incidence relationships in cervical SCC and adenocarcinoma diagnosed in years 1958-1996, including a total of 15,118 and 1866 cases, respectively. Area of residence and socio-economic status were included in analyses because they were risk factors of cervical cancer. The analysis of cervical SCC confirmed an incidence maximum at ages 35-39 years. The data for adenocarcinoma also suggested a similar early age maximum but the curves differed extensively by birth cohort. The incidence of adenocarcinoma increased substantially at young age groups towards the end of follow-up. Endometrial adenocarcinoma and vaginal and vulvar SCC, which share some risk factors with cervical cancer, did not show an early age incidence maximum. The results also showed that there was a decrease in the incidence of cervical SCC around year 1960, almost 10 years before the organized population screening, probably due to introduced opportunistic pap testing. The benefits of the organized screening were observed as a further decline in the incidence rates. The unique age-incidence relationships in cervical cancer call for biological explanations.