title: Cancer risk in children with birth defects and in their families: a population based cohort study of 5.2 million children from Norway and Sweden.
abstract: BACKGROUND
  Cancer and birth defects may share factors that influence risk. A malformation may involve physiologic changes or changes in lifestyle that might affect cancer risks.
  
  
  METHODS
  In Norway and Sweden, the population-based medical birth and cancer registries were linked to identify subsequent cancer occurrence in children with birth defects and among their parents and siblings. Altogether, 5.2 million children and their families were included. The standardized incidence ratio (SIR) served as a measure of relative risk.
  
  
  RESULTS
  There was an increased overall cancer risk in individuals with birth defects in the two countries [SIR, 1.7; 95% confidence interval (95% CI), 1.6-1.9], and the increased risk remained into early adulthood. Individuals with malformations in the nervous system were at increased risk of developing cancer in the brain/nervous system (Norway: SIR, 58; 95% CI, 41-80; Sweden: SIR, 8.3; 95% CI, 4.0-15), individuals with Down syndrome were at an increased risk of leukemia (Norway: SIR, 36; 95% CI, 26-48; Sweden: SIR, 36; 95% CI, 28-46), and there was an increased overall cancer risk for individuals with multiple birth defects (Norway: SIR, 5.5; 95% CI, 3.3-8.7; Sweden: SIR, 3.6; 95% CI, 2.2-5.4). There was no increased overall cancer risk among mothers (SIR, 1.0; 95% CI, 1.0-1.0), fathers (SIR, 1.0; 95% CI, 0.9-1.0), and siblings (SIR, 1.0; 95% CI, 0.9-1.1) of children with birth defects.
  
  
  CONCLUSIONS
  We observed an increased overall cancer risk in individuals with birth defects. The highest risks were seen for individuals with malformations in the nervous system, Down syndrome, and multiple defects. No increased overall cancer risk was seen among their parents or siblings.
authors.affiliation: Section for Epidemiology and Medical Statistics, Department of Public Health and Primary Health Care, University of Bergen, N-5018 Bergen, Norway. tone.bjorge@isf.uib.no
authors.forename: Tone
authors.initials: T
authors.lastname: Bjørge
authors.forename: Sven
authors.initials: S
authors.lastname: Cnattingius
authors.forename: Rolv Terje
authors.initials: RT
authors.lastname: Lie
authors.forename: Steinar
authors.initials: S
authors.lastname: Tretli
authors.forename: Anders
authors.initials: A
authors.lastname: Engeland
mesh_terms: D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D000013:Congenital Abnormalities / Q000145:classification / Q000453:epidemiology*; D005192:Family Health; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009369:Neoplasms / Q000453:epidemiology*; D009664:Norway / Q000453:epidemiology; D012042:Registries; D018570:Risk Assessment; D013548:Sweden / Q000453:epidemiology