50 years of screening in the Nordic countries: quantifying the effects on cervical cancer incidence

Abstract

Background: Nordic countries' data offer a unique possibility to evaluate the long-term benefit of cervical cancer screening in a context of increasing risk of human papillomavirus infection.

Methods: Ad hoc-refined age-period-cohort models were applied to the last 50-year incidence data from Denmark, Finland, Norway and Sweden to project expected cervical cancer cases in a no-screening scenario.

Results: In the absence of screening, projected incidence rates for 2006-2010 in Nordic countries would have been between 3 and 5 times higher than observed rates. Over 60,000 cases or between 41 and 49% of the expected cases of cervical cancer may have been prevented by the introduction of screening in the late 1960s and early 1970s.

Conclusions: Our study suggests that screening programmes might have prevented a HPV-driven epidemic of cervical cancer in Nordic countries. According to extrapolations from cohort effects, cervical cancer incidence rates in the Nordic countries would have been otherwise comparable to the highest incidence rates currently detected in low-income countries.

Figure 1

Effect of age, period and cohort on observed and projected ASRs of incident cervical cancer. Age-standardised rates (ASRs) are plotted by period. Age effects and ASRs are shown on a rate per 100 000 scale; cohort and period effects are on a relative risk scale. Reference points for period and cohort rate ratios are marked. Under a scenario without screening activities, period effects are forced to assume a constant value over time (dot-dashed lines). The projected ASRs corresponding to period effects constant over time, but age and cohort effects as estimated by the model, are also shown (dashed thick lines).