title: [Cancer in siblings of children with cancer].
abstract: BACKGROUND
  In some rare inherited disorders, such as Li-Fraumeni syndrome, relatives of children with cancer are at increased risk of cancer. We aimed to assess relations between childhood cancer and sibling risk, and evaluate the influence of recessive conditions in cancer causation.
  
  
  METHODS
  We did a population-based cohort study in the Nordic countries of 42,277 siblings of 25,605 children with cancer. Children with cancer were identified from records in the five Nordic cancer registries, and their siblings from nationwide population registries. Cancers in siblings were documented through record linkage with cancer registries and compared with national incidence rates. We also assessed cancer incidence in parents to identify familial cancer syndromes.
  
  
  RESULTS
  284.2 cancers were expected in siblings, whereas 353 were diagnosed (standardised incidence ratio 1.24 95% CI, 1.12-1.38). Risk ratios for siblings were highest in the first decade of life (2.59; 1.89-3.46). We excluded 56 families with genetic syndromes linked to cancer, which reduced this ratio from 1.7 to 1.0 (0.7-1.3) for siblings younger than 20 years and from 1.3 to 1.0 (0.8-1.3) for those aged 20-29 years. We found no new patterns of familial cancer that indicated inherited susceptibility, or evidence that recessive conditions might contribute to cancers not explained by syndromes. 40% of cancers in siblings that occurred before age 20 years could be attributed to known genetic factors, whereas 60% remained unexplained.
  
  
  CONCLUSIONS
  Apart from rare cancer syndromes, paediatric cancer is not an indicator of increased risk in siblings.
authors.affiliation: Institut for Epidemiologisk Kraeftforskning, Kraeftens Bekaempelse, Strandboulevarden 49, DK-2100 København ø. jeanette@cancer.dk
authors.forename: Jeanette Falck
authors.initials: JF
authors.lastname: Winther
authors.forename: Risto
authors.initials: R
authors.lastname: Sankila
authors.forename: John D
authors.initials: JD
authors.lastname: Boice
authors.forename: Hrafn
authors.initials: H
authors.lastname: Tulinius
authors.forename: Andrea
authors.initials: A
authors.lastname: Bautz
authors.forename: Lotti
authors.initials: L
authors.lastname: Barlow
authors.forename: Eystein
authors.initials: E
authors.lastname: Glattre
authors.forename: Frøydis
authors.initials: F
authors.lastname: Langmark
authors.forename: Torgil
authors.initials: T
authors.lastname: Möller
authors.forename: John J
authors.initials: JJ
authors.lastname: Mulvihill
authors.forename: Gudridur H
authors.initials: GH
authors.lastname: Olafsdottir
authors.forename: Annukka
authors.initials: A
authors.lastname: Ritvanen
authors.forename: Jørgen H
authors.initials: JH
authors.lastname: Olsen
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D005387:Finland / Q000453:epidemiology; D020022:Genetic Predisposition to Disease; D006801:Humans; D015994:Incidence; D007223:Infant; D008297:Male; D009369:Neoplasms / Q000453:epidemiology / Q000235:genetics*; D009679:Nuclear Family; D016017:Odds Ratio; D012042:Registries; D012307:Risk Factors; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology