title: Screening mammography & breast cancer mortality: meta-analysis of quasi-experimental studies.
abstract: BACKGROUND
  The magnitude of the benefit associated with screening has been debated. We present a meta-analysis of quasi-experimental studies on the effects of mammography screening.
  
  
  METHODS
  We searched MEDLINE/PubMed and Embase for articles published through January 31, 2013. Studies were included if they reported: 1) a population-wide breast cancer screening program using mammography with 5+ years of data post-implementation; 2) a comparison group with equal access to therapies; and 3) breast cancer mortality. Studies excluded were: RCTs, case-control, or simulation studies. We defined quasi-experimental as studies that compared either geographical, historical or birth cohorts with a screening program to an equivalent cohort without a screening program. Meta-analyses were conducted in Stata using the metan command, random effects. Meta-analyses were conducted separately for ages screened: under 50, 50 to 69 and over 70 and weighted by population and person-years.
  
  
  RESULTS
  Among 4,903 published papers that were retrieved, 19 studies matched eligibility criteria. Birth cohort studies reported a significant benefit for women screened <age 50, but not for women screened ages 50-69. Significant reductions in breast cancer mortality were observed in historical comparisons. For geographical comparisons, there was a significant 20% reduction in mortality for women <age 50 and a significant 21-22% reduction for women ages 50-69. Studies that tested the interaction of geographical and historical comparisons produced a pooled, significant 13-17% reduction in incident breast cancer mortality for women ages 50-69, but the effects in most individual studies were non-significant. All studies of women ages 70+ were non-significant.
  
  
  CONCLUSIONS
  Mammography screening may have modest effects on cancer mortality between the ages of 50 and 69 and non-significant effects for women older than age 70. Results are consistent with meta-analyses of RCTs. Effects on total mortality could not be assessed because of the limited number of studies.
authors.affiliation: Department of Rehabilitation Medicine, Clinical Research Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Veronica L
authors.initials: VL
authors.lastname: Irvin
authors.affiliation: Department of Rehabilitation Medicine, Clinical Research Center, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Robert M
authors.initials: RM
authors.lastname: Kaplan
mesh_terms: D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality*; D015331:Cohort Studies; D016001:Confidence Intervals; D055088:Early Detection of Cancer; D005260:Female; D005843:Geography; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D017594:Publication Bias; D012307:Risk Factors