Eight RCTs (n= 210,840 participants), two uncontrolled retrospective studies (n=218,077 screening examinations), five meta-analyses/systematic reviews, two further critical appraisal reports and four guidelines.
Randomised controlled trials (n=8):
None of the trials directly addressed the issue of appropriate screening intervals. Screening intervals ranged from 12-33mths.
The relative risk of death was only significant in two out of the eight studies and in these studies ranged from 0.55 (95% CI: 0.31, 0.96) to 0.64 (95% CI: 0.45, 0.89) comparing screening to non-screening control groups. The corresponding ARRs ranged from 0.12 to 0.21.
Uncontrolled retrospective studies (n=2):
One study concluded that annual mammography screening resulted in a lower recall rate and smaller (invasive) tumour size as compared with biennial screening. The other study concluded that mammography screening was less effective in younger (40-49yrs) as opposed to older women (50+yrs).
Meta-analyses/systematic reviews (n=5):
Three analyses showed no statistically significant reduction in the mortality rate through using screening mammography. The remaining two showed a statistically significant reduction in mortality amongst those women who were screened as opposed to those who were not (16-18% reduction in mortality).
Critical appraisal reports (n=2):
One review concluded that screening for breast cancer using mammography was unjustified and the other concluded that the benefit of biennial screening from age 40yrs is modest and the harms and costs are not inconsequential.
Only one of the guidelines rated the quality and strength of the evidence using a rating scheme. Overall, the guidelines were not consistent in relation to age at which screening should begin or the frequency of the screens in the different age groups.