title: Breast cancer screening for women ages 50 to 69 years a systematic review of observational evidence.
abstract: OBJECTIVE
  To systematically review the observational evidence concerning the effect of screening on breast cancer mortality in actual populations of women ages 50-69 years.
  
  
  METHODS
  We searched MEDLINE and multiple reference lists for relevant cohort and ecologic studies. At least 2 authors reviewed abstracts and full texts of studies meeting eligibility criteria. We rated each accepted study on standard quality criteria and developed a Summary Evidence Table.
  
  
  RESULTS
  Seventeen studies met eligibility criteria. Five studies found no to small effect of screening (0-12% relative risk reduction [RRR] in breast cancer mortality), 4 found a large effect (greater than 33% RRR), and 8 found a moderate effect (13% to 33% reduction). The authors found concerns about quality in all studies. There was insufficient evidence to determine whether the effectiveness of screening is decreasing over time.
  
  
  CONCLUSIONS
  Current observational evidence shows that breast cancer screening in actual populations of women ages 50 to 69 reduces breast cancer mortality; the magnitude of the effect is probably smaller than predicted in the randomized controlled trials. Because the magnitude may change (either increase or decrease) in the future, further ecologic studies are needed. The methodology and infrastructure for these studies should be improved.
authors.affiliation: Division of General Medicine and Clinical Epidemiology and Cecil G. Sheps Center for Health Services Research, University of North Carolina School of Medicine, Chapel Hill, NC, USA. rharris@med.unc.edu
authors.forename: Russell
authors.initials: R
authors.lastname: Harris
authors.forename: John
authors.initials: J
authors.lastname: Yeatts
authors.forename: Linda
authors.initials: L
authors.lastname: Kinsinger
mesh_terms: D000367:Age Factors; D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality; D055088:Early Detection of Cancer / Q000379:methods* / Q000706:statistics & numerical data; D019317:Evidence-Based Medicine / Q000379:methods*; D005260:Female; D006801:Humans; D008875:Middle Aged; D011315:Preventive Medicine / Q000379:methods; D012107:Research Design; D040242:Risk Reduction Behavior; D013997:Time Factors; D014481:United States; D016387:Women's Health / Q000706:statistics & numerical data*