title: Environmental and heritable factors in the causation of cancer--analyses of cohorts of twins from Sweden, Denmark, and Finland.
abstract: BACKGROUND
  The contribution of hereditary factors to the causation of sporadic cancer is unclear. Studies of twins make it possible to estimate the overall contribution of inherited genes to the development of malignant diseases.
  
  
  METHODS
  We combined data on 44,788 pairs of twins listed in the Swedish, Danish, and Finnish twin registries in order to assess the risks of cancer at 28 anatomical sites for the twins of persons with cancer. Statistical modeling was used to estimate the relative importance of heritable and environmental factors in causing cancer at 11 of those sites.
  
  
  RESULTS
  At least one cancer occurred in 10,803 persons among 9512 pairs of twins. An increased risk was found among the twins of affected persons for stomach, colorectal, lung, breast, and prostate cancer. Statistically significant effects of heritable factors were observed for prostate cancer (42 percent; 95 percent confidence interval, 29 to 50 percent), colorectal cancer (35 percent; 95 percent confidence interval, 10 to 48 percent), and breast cancer (27 percent; 95 percent confidence interval, 4 to 41 percent).
  
  
  CONCLUSIONS
  Inherited genetic factors make a minor contribution to susceptibility to most types of neoplasms. This finding indicates that the environment has the principal role in causing sporadic cancer. The relatively large effect of heritability in cancer at a few sites suggests major gaps in our knowledge of the genetics of cancer.
authors.affiliation: Department of Medical Epidemiology, Karolinska Institute, Stockholm, Sweden. paul.lichtenstein@mep.ki.se
authors.forename: P
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: N V
authors.initials: NV
authors.lastname: Holm
authors.forename: P K
authors.initials: PK
authors.lastname: Verkasalo
authors.forename: A
authors.initials: A
authors.lastname: Iliadou
authors.forename: J
authors.initials: J
authors.lastname: Kaprio
authors.forename: M
authors.initials: M
authors.lastname: Koskenvuo
authors.forename: E
authors.initials: E
authors.lastname: Pukkala
authors.forename: A
authors.initials: A
authors.lastname: Skytthe
authors.forename: K
authors.initials: K
authors.lastname: Hemminki
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000235:genetics; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000235:genetics; D003718:Denmark; D004200:Diseases in Twins / Q000209:etiology* / Q000235:genetics*; D004777:Environment; D005260:Female; D005387:Finland; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009369:Neoplasms / Q000209:etiology* / Q000235:genetics*; D011471:Prostatic Neoplasms / Q000235:genetics; D012042:Registries; D012306:Risk; D013548:Sweden; D014429:Twins, Dizygotic / Q000235:genetics; D014430:Twins, Monozygotic / Q000235:genetics