title: Modern mammography screening and breast cancer mortality: population study.
abstract: OBJECTIVE
  To evaluate the effectiveness of contemporary mammography screening using individual information about screening history and breast cancer mortality from public screening programmes.
  
  
  METHODS
  Prospective cohort study of Norwegian women who were followed between 1986 and 2009. Within that period (1995-2005), a national mammography screening programme was gradually implemented, with biennial invitations sent to women aged 50-69 years.
  
  
  METHODS
  All Norwegian women aged 50-79 between 1986 and 2009.
  
  
  METHODS
  Multiple Poisson regression analysis was used to estimate breast cancer mortality rate ratios comparing women who were invited to screening (intention to screen) with women who were not invited, with a clear distinction between cases of breast cancer diagnosed before (without potential for screening effect) and after (with potential for screening effect) the first invitation for screening. We took competing causes of death into account by censoring women from further follow-up who died from other causes. Based on the observed mortality reduction combined with the all cause and breast cancer specific mortality in Norway in 2009, we used the CISNET (Cancer Intervention and Surveillance Modeling Network) Stanford simulation model to estimate how many women would need to be invited to biennial mammography screening in the age group 50-69 years to prevent one breast cancer death during their lifetime.
  
  
  RESULTS
  During 15 193 034 person years of observation (1986-2009), deaths from breast cancer occurred in 1175 women with a diagnosis after being invited to screening and 8996 women who had not been invited before diagnosis. After adjustment for age, birth cohort, county of residence, and national trends in deaths from breast cancer, the mortality rate ratio associated with being invited to mammography screening was 0.72 (95% confidence interval 0.64 to 0.79). To prevent one death from breast cancer, 368 (95% confidence interval 266 to 508) women would need to be invited to screening.
  
  
  CONCLUSIONS
  Invitation to modern mammography screening may reduce deaths from breast cancer by about 28%.
authors.affiliation: Department of Public Health, Norwegian University of Science and Technology, 7491 Trondheim, Norway Oslo Center for Biostatistics and Epidemiology, Department of Biostatistics, University of Oslo, Oslo, Norway Oslo Center for Biostatistics and Epidemiology, Research Support Services, Oslo University Hospital, Oslo, Norway harald.weedon-fekjar@medisin.uio.no.
authors.forename: Harald
authors.initials: H
authors.lastname: Weedon-Fekjær
authors.affiliation: Department of Public Health, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
authors.forename: Pål R
authors.initials: PR
authors.lastname: Romundstad
authors.affiliation: Department of Public Health, Norwegian University of Science and Technology, 7491 Trondheim, Norway Harvard School of Public Health, Department of Epidemiology, Boston, MA, USA.
authors.forename: Lars J
authors.initials: LJ
authors.lastname: Vatten
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000000981:diagnostic imaging*; D055088:Early Detection of Cancer / Q000379:methods / Q000639:trends; D005260:Female; D006801:Humans; D008327:Mammography; D008875:Middle Aged; D011446:Prospective Studies