Twenty-one studies were included in the review, comprising one RCT (97,627 women), two cohort studies (780,251 women) and 18 case-control studies (75,892 women).
The RCT showed that screening significantly reduced the risk of mortality (RR 0.65, 95% CI 0.47 to 0.90) and incidence of advanced cervical cancer (RR 0.56, 95% CI 0.42 to 0.75), but not the overall incidence of cervical cancer (RR 1.12, 95% CI 0.91 to 1.39). The quality of evidence was moderate for all outcomes.
One UK cohort study (rated as low quality evidence) reported that cytology significantly reduced the risk of invasive cervical cancer (RR 0.38, 95% CI 0.23 to 0.63).
Pooled data from 12 case-control studies (rated as very low quality evidence) suggested a statistically significant protective effect of screening (OR 0.35, 95% CI 0.30 to 0.41; Ι²=76%). Heterogeneity was substantially reduced in most post-hoc sensitivity analysis (results reported in the paper).
Limited evidence on screening intervals and age groups were also discussed in the paper.