title: Swedish two-county trial: impact of mammographic screening on breast cancer mortality during 3 decades.
abstract: OBJECTIVE
  To estimate the long-term (29-year) effect of mammographic screening on breast cancer mortality in terms of both relative and absolute effects.
  
  
  METHODS
  This study was carried out under the auspices of the Swedish National Board of Health and Welfare. The board determined that, because randomization was at a community level and was to invitation to screening, informed verbal consent could be given by the participants when they attended the screening examination. A total of 133 065 women aged 40-74 years residing in two Swedish counties were randomized into a group invited to mammographic screening and a control group receiving usual care. Case status and cause of death were determined by the local trial end point committees and, independently, by an external committee. Mortality analysis was performed by using negative binomial regression.
  
  
  RESULTS
  There was a highly significant reduction in breast cancer mortality in women invited to screening according to both local end point committee data (relative risk [RR] = 0.69; 95% confidence interval: 0.56, 0.84; P < .0001) and consensus data (RR = 0.73; 95% confidence interval: 0.59, 0.89; P = .002). At 29 years of follow-up, the number of women needed to undergo screening for 7 years to prevent one breast cancer death was 414 according to local data and 519 according to consensus data. Most prevented breast cancer deaths would have occurred (in the absence of screening) after the first 10 years of follow-up.
  
  
  CONCLUSIONS
  Invitation to mammographic screening results in a highly significant decrease in breast cancer-specific mortality. Evaluation of the full impact of screening, in particular estimates of absolute benefit and number needed to screen, requires follow-up times exceeding 20 years because the observed number of breast cancer deaths prevented increases with increasing time of follow-up.
authors.affiliation: Department of Mammography, Falun Central Hospital, Falun, Sweden.
authors.forename: László
authors.initials: L
authors.lastname: Tabár
authors.forename: Bedrich
authors.initials: B
authors.lastname: Vitak
authors.forename: Tony Hsiu-Hsi
authors.initials: TH
authors.lastname: Chen
authors.forename: Amy Ming-Fang
authors.initials: AM
authors.lastname: Yen
authors.forename: Anders
authors.initials: A
authors.lastname: Cohen
authors.forename: Tibor
authors.initials: T
authors.lastname: Tot
authors.forename: Sherry Yueh-Hsia
authors.initials: SY
authors.lastname: Chiu
authors.forename: Sam Li-Sheng
authors.initials: SL
authors.lastname: Chen
authors.forename: Jean Ching-Yuan
authors.initials: JC
authors.lastname: Fann
authors.forename: Johan
authors.initials: J
authors.lastname: Rosell
authors.forename: Helena
authors.initials: H
authors.lastname: Fohlin
authors.forename: Robert A
authors.initials: RA
authors.lastname: Smith
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Duffy
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000401:mortality / Q000517:prevention & control; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000706:statistics & numerical data*; D008403:Mass Screening / Q000706:statistics & numerical data*; D008875:Middle Aged; D018570:Risk Assessment; D012307:Risk Factors; D016019:Survival Analysis; D015996:Survival Rate; D013548:Sweden