title: Familial Risk and Heritability of Cancer Among Twins in Nordic Countries.
abstract: OBJECTIVE
  Estimates of familial cancer risk from population-based studies are essential components of cancer risk prediction.
  
  
  OBJECTIVE
  To estimate familial risk and heritability of cancer types in a large twin cohort.
  
  
  METHODS
  Prospective study of 80,309 monozygotic and 123,382 same-sex dizygotic twin individuals (N = 203,691) within the population-based registers of Denmark, Finland, Norway, and Sweden. Twins were followed up a median of 32 years between 1943 and 2010. There were 50,990 individuals who died of any cause, and 3804 who emigrated and were lost to follow-up.
  
  
  METHODS
  Shared environmental and heritable risk factors among pairs of twins.
  
  
  METHODS
  The main outcome was incident cancer. Time-to-event analyses were used to estimate familial risk (risk of cancer in an individual given a twin's development of cancer) and heritability (proportion of variance in cancer risk due to interindividual genetic differences) with follow-up via cancer registries. Statistical models adjusted for age and follow-up time, and accounted for censoring and competing risk of death.
  
  
  RESULTS
  A total of 27,156 incident cancers were diagnosed in 23,980 individuals, translating to a cumulative incidence of 32%. Cancer was diagnosed in both twins among 1383 monozygotic (2766 individuals) and 1933 dizygotic (2866 individuals) pairs. Of these, 38% of monozygotic and 26% of dizygotic pairs were diagnosed with the same cancer type. There was an excess cancer risk in twins whose co-twin was diagnosed with cancer, with estimated cumulative risks that were an absolute 5% (95% CI, 4%-6%) higher in dizygotic (37%; 95% CI, 36%-38%) and an absolute 14% (95% CI, 12%-16%) higher in monozygotic twins (46%; 95% CI, 44%-48%) whose twin also developed cancer compared with the cumulative risk in the overall cohort (32%). For most cancer types, there were significant familial risks and the cumulative risks were higher in monozygotic than dizygotic twins. Heritability of cancer overall was 33% (95% CI, 30%-37%). Significant heritability was observed for the cancer types of skin melanoma (58%; 95% CI, 43%-73%), prostate (57%; 95% CI, 51%-63%), nonmelanoma skin (43%; 95% CI, 26%-59%), ovary (39%; 95% CI, 23%-55%), kidney (38%; 95% CI, 21%-55%), breast (31%; 95% CI, 11%-51%), and corpus uteri (27%; 95% CI, 11%-43%).
  
  
  CONCLUSIONS
  In this long-term follow-up study among Nordic twins, there was significant excess familial risk for cancer overall and for specific types of cancer, including prostate, melanoma, breast, ovary, and uterus. This information about hereditary risks of cancers may be helpful in patient education and cancer risk counseling.
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts2Division of Public Health Sciences, University of Iceland, Reykjavik3Channing Division of Network Medicine, Brigham and Women's Hospital, Harvard Medical School.
authors.forename: Lorelei A
authors.initials: LA
authors.lastname: Mucci
authors.affiliation: Department of Biostatistics and Epidemiology, University of Southern Denmark, Odense5Danish Twin Registry, University of Southern Denmark, Odense.
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Hjelmborg
authors.affiliation: Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Harris
authors.affiliation: Department of Biostatistics and Epidemiology, University of Southern Denmark, Odense5Danish Twin Registry, University of Southern Denmark, Odense7Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Kamila
authors.initials: K
authors.lastname: Czene
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts.
authors.forename: David J
authors.initials: DJ
authors.lastname: Havelick
authors.affiliation: Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Scheike
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts9Department of Epidemiology and Biostatistics, University of California, San Francisco.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Graff
authors.affiliation: Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Klaus
authors.initials: K
authors.lastname: Holst
authors.affiliation: Department of Biostatistics and Epidemiology, University of Southern Denmark, Odense5Danish Twin Registry, University of Southern Denmark, Odense.
authors.forename: Sören
authors.initials: S
authors.lastname: Möller
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Unger
authors.affiliation: Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts.
authors.forename: Christina
authors.initials: C
authors.lastname: McIntosh
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Nuttall
authors.affiliation: Division of Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Ingunn
authors.initials: I
authors.lastname: Brandt
authors.affiliation: Channing Division of Network Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts.
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Penney
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden11Department of Surgery, National University Hospital and NUHS, Singapore.
authors.forename: Mikael
authors.initials: M
authors.lastname: Hartman
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts10Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts.
authors.forename: Peter
authors.initials: P
authors.lastname: Kraft
authors.affiliation: Department of Biostatistics, Harvard T. H. Chan School of Public Health, Boston, Massachusetts12Department of Computational Biology and Biostatistics, Dana Farber Cancer Institute, Boston, Massachusetts.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Parmigiani
authors.affiliation: Department of Biostatistics and Epidemiology, University of Southern Denmark, Odense.
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
authors.affiliation: University of Helsinki, Hjelt Institute, Department of Public Health, Helsinki, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Koskenvuo
authors.affiliation: Danish Twin Registry, University of Southern Denmark, Odense14Department of Oncology, Odense University Hospital, Odense, Denmark.
authors.forename: Niels V
authors.initials: NV
authors.lastname: Holm
authors.affiliation: University of Helsinki, Hjelt Institute, Department of Public Health, Helsinki, Finland.
authors.forename: Kauko
authors.initials: K
authors.lastname: Heikkilä
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Helsinki, Finland16School of Health Sciences, University of Tampere, Tampere, Finland.
authors.forename: Eero
authors.initials: E
authors.lastname: Pukkala
authors.affiliation: Department of Biostatistics and Epidemiology, University of Southern Denmark, Odense5Danish Twin Registry, University of Southern Denmark, Odense.
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthe
authors.affiliation: Department of Epidemiology, Harvard T. H. Chan School of Public Health, Boston, Massachusetts7Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Hans-Olov
authors.initials: HO
authors.lastname: Adami
authors.affiliation: University of Helsinki, Hjelt Institute, Department of Public Health, Helsinki, Finland17National Institute for Health and Welfare, Department of Health, Helsinki, Finland18University of Helsinki, Institute for Molecular Medicine, Helsinki, Finland.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D059647:Gene-Environment Interaction; D006801:Humans; D015994:Incidence; D008297:Male; D009369:Neoplasms / Q000453:epidemiology* / Q000235:genetics*; D009664:Norway / Q000453:epidemiology; D011446:Prospective Studies; D018570:Risk Assessment; D013548:Sweden / Q000453:epidemiology; D013997:Time Factors; D014429:Twins, Dizygotic / Q000706:statistics & numerical data; D014430:Twins, Monozygotic / Q000706:statistics & numerical data