title: Fathering of dizygotic twins and risk of prostate cancer: nationwide, population-based case-control study.
abstract: BACKGROUND
  An association between male fertility and risk of prostate cancer has been suggested, possibly through lower androgen levels in subfertile men. We evaluated male fertility in relation to risk of prostate cancer by assessing the frequency of fathering of dizygotic twins, a marker of high fertility, among cases of prostate cancer and controls.
  
  
  METHODS
  We performed a case-control study in Prostate Cancer data Base Sweden (PCBaSe), a nationwide, population-based cohort. PCBaSe was linked to the Swedish twin register for information on zygosity for same-sex twins and to other nationwide health care registers and demographic databases for information on socioeconomic factors, comorbidity, and tumor characteristics for 96 301 prostate cancer cases and 378 583 matched controls. To account for the influence of in vitro fertilization on dizygotic twinning, analyses were restricted to men who had fathered children before 1991, when in vitro fertilization was still uncommon in Sweden.
  
  
  RESULTS
  1 112 cases and 4 538 controls had fathered dizygotic twins. Men with dizygotic twins had no increased risk of prostate cancer compared to fathers of singletons; neither for total prostate cancer odds ratio (OR) 0.95(95% CI 0.89-1.02), nor for any risk category, OR 0.97 (95% CI 0.84-1.12) for low-risk disease, and OR 1.04 (95% CI 0.90-1.22) for metastatic disease.
  
  
  CONCLUSIONS
  The lack of association between fathering of dizygotic twins and prostate cancer risk give no support for an association between male fertility and prostate cancer risk.
authors.affiliation: Department of Surgery and Perioperative Sciences, Urology and Andrology, Umeå University, Umeå, Sweden.
authors.forename: Sara
authors.initials: S
authors.lastname: Wirén
authors.affiliation: Regional Cancer Centre, Uppsala University Hospital, Uppsala, Sweden.
authors.forename: Linda
authors.initials: L
authors.lastname: Drevin
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Olof
authors.initials: O
authors.lastname: Akre
authors.affiliation: Department of Urology, Ryhov County Hospital, Jönköping, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Robinson
authors.affiliation: Department of Surgery and Perioperative Sciences, Urology and Andrology, Umeå University, Umeå, Sweden.
authors.forename: Pär
authors.initials: P
authors.lastname: Stattin
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005298:Fertility; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000453:epidemiology* / Q000209:etiology; D012306:Risk; D013548:Sweden / Q000453:epidemiology; D014429:Twins, Dizygotic