title: Mammographic density and the risk and detection of breast cancer.
abstract: BACKGROUND
  Extensive mammographic density is associated with an increased risk of breast cancer and makes the detection of cancer by mammography difficult, but the influence of density on risk according to method of cancer detection is unknown.
  
  
  METHODS
  We carried out three nested case-control studies in screened populations with 1112 matched case-control pairs. We examined the association of the measured percentage of density in the baseline mammogram with risk of breast cancer, according to method of cancer detection, time since the initiation of screening, and age.
  
  
  RESULTS
  As compared with women with density in less than 10% of the mammogram, women with density in 75% or more had an increased risk of breast cancer (odds ratio, 4.7; 95% confidence interval [CI], 3.0 to 7.4), whether detected by screening (odds ratio, 3.5; 95% CI, 2.0 to 6.2) or less than 12 months after a negative screening examination (odds ratio, 17.8; 95% CI, 4.8 to 65.9). Increased risk of breast cancer, whether detected by screening or other means, persisted for at least 8 years after study entry and was greater in younger than in older women. For women younger than the median age of 56 years, 26% of all breast cancers and 50% of cancers detected less than 12 months after a negative screening test were attributable to density in 50% or more of the mammogram.
  
  
  CONCLUSIONS
  Extensive mammographic density is strongly associated with the risk of breast cancer detected by screening or between screening tests. A substantial fraction of breast cancers can be attributed to this risk factor.
authors.affiliation: Campbell Family Institute for Breast Cancer Research, Toronto, ON, Canada. boyd@uhnres.utoronto.ca
authors.forename: Norman F
authors.initials: NF
authors.lastname: Boyd
authors.forename: Helen
authors.initials: H
authors.lastname: Guo
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Martin
authors.forename: Limei
authors.initials: L
authors.lastname: Sun
authors.forename: Jennifer
authors.initials: J
authors.lastname: Stone
authors.forename: Eve
authors.initials: E
authors.lastname: Fishell
authors.forename: Roberta A
authors.initials: RA
authors.lastname: Jong
authors.forename: Greg
authors.initials: G
authors.lastname: Hislop
authors.forename: Anna
authors.initials: A
authors.lastname: Chiarelli
authors.forename: Salomon
authors.initials: S
authors.lastname: Minkin
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Yaffe
mesh_terms: D000328:Adult; D000368:Aged; D001940:Breast / Q000473:pathology; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000453:epidemiology / Q000473:pathology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008327:Mammography; D008875:Middle Aged; D012306:Risk