title: Bias versus causality: interpreting recent evidence of association between endometriosis and ovarian cancer.
abstract: OBJECTIVE
  To establish whether causality versus biases may explain the association of endometriosis and ovarian cancer.
  
  
  METHODS
  We employ the nine criteria proposed by Austin Bradford Hill, which still stand as foundation milestones for causal inference.
  
  
  METHODS
  University-based clinic.
  
  
  METHODS
  None.
  
  
  METHODS
  Search strategies included online searching of the MEDLINE database and hand searching of relevant publications and reviews. Additional reports were collected by systematically reviewing all references from retrieved papers.
  
  
  METHODS
  Examination of the causal relationship between endometriosis and ovarian cancer.
  
  
  RESULTS
  Based on the present analysis, the criterion of strength has not been fulfilled. There were insufficient or mixed data for four criteria (biological gradient, biological plausibility, analogy, coherence), and four criteria were fulfilled (consistency, temporality, specificity, experimental evidence in animal model).
  
  
  CONCLUSIONS
  A causal relationship between endometriosis and specific histotypes of ovarian cancer should be recognized, but the low magnitude of the risk observed is consistent with the view that ectopic endometrium undergoes malignant transformation with a frequency similar to its eutopic counterpart.
authors.affiliation: Department of Obstetrics and Gynecology, Fondazione Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milan, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: Viganò
authors.forename: Edgardo
authors.initials: E
authors.lastname: Somigliana
authors.forename: Fabio
authors.initials: F
authors.lastname: Parazzini
authors.forename: Paolo
authors.initials: P
authors.lastname: Vercellini
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D004715:Endometriosis / Q000209:etiology*; D005260:Female; D006801:Humans; D015588:Observer Variation; D010051:Ovarian Neoplasms / Q000453:epidemiology*; D018579:Patient Selection; D011336:Probability; D015203:Reproducibility of Results; D012307:Risk Factors