Age-related incidence of cervical cancer supports two aetiological components: a population-based register study.

ABSTRACT

OBJECTIVE: To assess whether age-related incidence of cervical cancer supports two aetiological components and to assess trends in these components due to risk factors and to organised screening in Finland. DESIGN: Population-based register study. SETTING: Finnish Cancer Registry. POPULATION Cervical cancer cases and female population in Finland in 1953-2012. METHODS: Cervical cancer incidence was estimated using Poisson regression where age-specific incidence consists of two (early-age and late-age) normally distributed components. MAIN OUTCOME MEASURES: Accumulated net risks (incidences) and numbers of cancer cases attributed to each age-related component by calendar time. RESULTS: The accumulated cervical cancer incidence in 2008-2012 was only 30% of that in 1953-1962, before the screening started. The fit of the observed age-specific rates and the rates based on the two-component model was good. In 1953-62, the accumulated net risk ratio (RR; early-age versus late-age) was 0.42 (95% CI 0.29-0.61). The early-age component disappeared in 1973-77 (RR 0.00; 95% CI 0.00-0.08). Thereafter, the risk for the early-age component increased, whereas the risk for the late-age component decreased, and in 2008-2012 the RR was 0.55 (95% CI 0.24-0.89). CONCLUSIONS: In Finland, cervical cancer incidence has two age-related components which are likely to indicate differences in risk factors of each component. The trend in risk of both components followed the effects of organised screening. Furthermore, the risk related to the early-age component followed changes in risk factors, such as oncogenic HPV infections and other sexually transmitted diseases and smoking habits. TWEETABLE ABSTRACT Cervical cancer incidence has two age-related components which are likely to have differencies in their aetiology.