Impact of cervical screening on cervical cancer mortality: estimation using stage-specific results from a nested case-control study.
BACKGROUND: It is well established that screening can prevent cervical cancer, but the magnitude of the impact of regular screening on cervical cancer mortality is unknown. METHODS: Population-based case-control study using prospectively recorded cervical screening data, England 1988-2013. Case women had cervical cancer diagnosed during April 2007-March 2013 aged 25-79 years (N=11 619). Two cancer-free controls were individually age matched to each case. We used conditional logistic regression to estimate the odds ratio (OR) of developing stage-specific cancer for women regularly screened or irregularly screened compared with women not screened in the preceding 15 years. Mortality was estimated from excess deaths within 5 years of diagnosis using stage-specific 5-year relative survival from England with adjustment for age within stage based on SEER (Surveillance, Epidemiology and End Results, USA) data. RESULTS: In women aged 35-64 years, regular screening is associated with a 67% (95% confidence interval (CI): 62-73%) reduction in stage 1A cancer and a 95% (95% CI: 94-97%) reduction in stage 3 or worse cervical cancer: the estimated OR comparing regular (⩽5.5yearly) screening to no (or minimal) screening are 0.18 (95% CI: 0.16-0.19) for cancer incidence and 0.08 (95% CI: 0.07-0.09) for mortality. It is estimated that in England screening currently prevents 70% (95% CI: 66-73%) of cervical cancer deaths (all ages); however, if everyone attended screening regularly, 83% (95% CI: 82-84%) could be prevented. CONCLUSIONS: The association between cervical cancer screening and incidence is stronger in more advanced stage cancers, and screening is more effective at preventing death from cancer than preventing cancer itself.British Journal of Cancer advance online publication, 15 September 2016; doi:10.1038/bjc.2016.290 www.bjcancer.com.