title: A retrospective cohort study of vasectomy and prostate cancer in US men.
abstract: OBJECTIVE
  To examine the relationship between vasectomy and prostate cancer.
  
  
  METHODS
  Retrospective cohort study.
  
  
  METHODS
  Husbands of nurses in 11 large states in the United States.
  
  
  METHODS
  In questionnaires administered in 1976 and 1978, 14,607 married female participants of the Nurses' Health Study reported vasectomy as the couple's form of contraception. In 1989, we contacted these 14,607 women and 14,607 age-matched participants whose husbands had not had a vasectomy prior to 1978 to ascertain their husband's disease status between 1976 and 1989.
  
  
  METHODS
  Diagnosis of prostate cancer.
  
  
  RESULTS
  During the study period, from 1976 through 1989, 96 new cases of prostate cancer were diagnosed in the cohort. Vasectomy was associated with an increased risk of prostate cancer (age-adjusted relative risk, 1.56; 95% confidence interval, 1.03 to 2.37; P = .04). The relative risk of prostate cancer increased over time since vasectomy. Among men who had their vasectomy 20 or more years in the past, the relative risk of prostate cancer was 1.89 (95% confidence interval, 1.14 to 3.14; P = .005), and after excluding stage A and B cases, the relative risk was 2.06 (95% confidence interval, 0.95 to 4.43; P = .07). This elevated risk of prostate cancer among vasectomized men persisted when we adjusted for smoking, alcohol consumption, educational level, body mass index, and geographical area of residence.
  
  
  CONCLUSIONS
  These results support evidence from other epidemiologic studies that vasectomy increases risk of prostate cancer. A biological mechanism whereby vasectomy influences the rate of prostate cancer may be related to a diminished secretory rate of prostatic fluid following vasectomy, or, alternatively, to the postvasectomy immune response to sperm antigens, which may cross-react with tumor-associated antigens and suppress tumor immunosurveillance mechanisms.
authors.affiliation: Channing Laboratory, Department of Medicine, Harvard Medical School, Boston, MA 02115.
authors.forename: E
authors.initials: E
authors.lastname: Giovannucci
authors.forename: T D
authors.initials: TD
authors.lastname: Tosteson
authors.forename: F E
authors.initials: FE
authors.lastname: Speizer
authors.forename: A
authors.initials: A
authors.lastname: Ascherio
authors.forename: M P
authors.initials: MP
authors.lastname: Vessey
authors.forename: G A
authors.initials: GA
authors.lastname: Colditz
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011471:Prostatic Neoplasms / Q000453:epidemiology*; D012189:Retrospective Studies; D012307:Risk Factors; D014481:United States; D014659:Vasectomy / Q000706:statistics & numerical data