title: The Heritability of Breast Cancer among Women in the Nordic Twin Study of Cancer.
abstract: BACKGROUND
  Family history is an established risk factor for breast cancer. Although some important genetic factors have been identified, the extent to which familial risk can be attributed to genetic factors versus common environment remains unclear.
  
  
  METHODS
  We estimated the familial concordance and heritability of breast cancer among 21,054 monozygotic and 30,939 dizygotic female twin pairs from the Nordic Twin Study of Cancer, the largest twin study of cancer in the world. We accounted for left-censoring, right-censoring, as well as the competing risk of death.
  
  
  RESULTS
  From 1943 through 2010, 3,933 twins were diagnosed with breast cancer. The cumulative lifetime incidence of breast cancer taking competing risk of death into account was 8.1% for both zygosities, although the cumulative risk for twins whose co-twins had breast cancer was 28% among monozygotic and 20% among dizygotic twins. The heritability of liability to breast cancer was 31% [95% confidence interval (CI), 10%-51%] and the common environmental component was 16% (95% CI, 10%-32%). For premenopausal breast cancer these estimates were 27% and 12%, respectively, and for postmenopausal breast cancer 22% and 16%, respectively. The relative contributions of genetic and environmental factors were constant between ages 50 and 96. Our results are compatible with the Peto-Mack hypothesis.
  
  
  CONCLUSIONS
  Our findings indicate that familial factors explain almost half of the variation in liability to develop breast cancer, and results were similar for pre- and postmenopausal breast cancer
  
  
  CONCLUSIONS
  We estimate heritability of breast cancer, taking until now ignored sources of bias into account.
authors.affiliation: Epidemiology, Biostatistics, and Biodemography, Department of Public Health, University of Southern Denmark, Odense, Denmark. The Danish Twin Registry, University of Southern Denmark, Odense, Denmark. moeller@health.sdu.dk.
authors.forename: Sören
authors.initials: S
authors.lastname: Möller
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Channing Division of Network Medicine, Brigham and Women's Hospital, Boston, Massachusetts. Centre for Public Health Sciences, University of Iceland, Reykjavik, Iceland.
authors.forename: Lorelei A
authors.initials: LA
authors.lastname: Mucci
authors.affiliation: Division of Epidemiology, The Norwegian Institute of Public Health, Oslo, Norway.
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Harris
authors.affiliation: Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Scheike
authors.affiliation: Department of Biostatistics, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Klaus
authors.initials: K
authors.lastname: Holst
authors.affiliation: Epidemiology, Biostatistics, and Biodemography, Department of Public Health, University of Southern Denmark, Odense, Denmark.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Halekoh
authors.affiliation: Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Hans-Olov
authors.initials: HO
authors.lastname: Adami
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Kamila
authors.initials: K
authors.lastname: Czene
authors.affiliation: Epidemiology, Biostatistics, and Biodemography, Department of Public Health, University of Southern Denmark, Odense, Denmark. The Danish Twin Registry, University of Southern Denmark, Odense, Denmark.
authors.forename: Kaare
authors.initials: K
authors.lastname: Christensen
authors.affiliation: The Danish Twin Registry, University of Southern Denmark, Odense, Denmark. Department of Oncology, Odense University Hospital, Odense, Denmark.
authors.forename: Niels V
authors.initials: NV
authors.lastname: Holm
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Helsinki, Finland. School of Health Sciences, University of Tampere, Tampere, Finland.
authors.forename: Eero
authors.initials: E
authors.lastname: Pukkala
authors.affiliation: Epidemiology, Biostatistics, and Biodemography, Department of Public Health, University of Southern Denmark, Odense, Denmark. The Danish Twin Registry, University of Southern Denmark, Odense, Denmark.
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthe
authors.affiliation: Department of Public Health & Institute for Molecular Medicine, University of Helsinki, Helsinki, Finland. Department of Health, National Institute for Health & Welfare, Helsinki, Finland.
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.affiliation: Epidemiology, Biostatistics, and Biodemography, Department of Public Health, University of Southern Denmark, Odense, Denmark. The Danish Twin Registry, University of Southern Denmark, Odense, Denmark.
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Hjelmborg
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000235:genetics*; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000235:genetics; D015331:Cohort Studies; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D020022:Genetic Predisposition to Disease; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D011379:Prognosis; D012042:Registries; D012307:Risk Factors; D015996:Survival Rate; D013548:Sweden / Q000453:epidemiology; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*
chemical_list: D014408:Biomarkers, Tumor