title: Hydatidiform moles and the long-term risk of breast cancer (Sweden).
abstract: OBJECTIVE
  The etiology of breast cancer is only partially understood. Based on the findings that pregnancies reduce breast cancer risk, a possible inverse association between exposure to the placental hormone human chorionic gonadotropin (hCG) and the risk of breast cancer has been suggested. Hydatidiform mole, a gestational trophoblastic disease, is associated with a high expression of hCG. We performed a population-based cohort study in which women with a history of hydatidiform mole were followed up for future cancer outcomes.
  
  
  METHODS
  All 3371 women with a notification of hydatidiform mole in the Swedish Cancer Registry between 1958 and 1993 were followed up for future cancer outcomes by record linkages within the registry.
  
  
  RESULTS
  In a total of 57,075 person-years of follow-up, 59 women had a diagnosis of breast cancer during follow-up, yielding an overall standardized incidence ratio of 1.3 (95% CI 1.0-1.7).
  
  
  CONCLUSIONS
  This finding is not consistent with the hypothesis of a protective effect of hCG exposure on breast cancer risk, but rather suggests an adverse association.
authors.affiliation: Department of Medical Epidemiology, Karolinska Institute, Stockholm, Sweden. Gunnar.Erlandsson@mep.ki.se
authors.forename: G
authors.initials: G
authors.lastname: Erlandsson
authors.forename: E
authors.initials: E
authors.lastname: Weiderpass
authors.forename: M
authors.initials: M
authors.lastname: Lambe
authors.forename: A
authors.initials: A
authors.lastname: Ekbom
mesh_terms: D000328:Adult; D017677:Age Distribution; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000453:epidemiology*; D002822:Choriocarcinoma / Q000175:diagnosis / Q000453:epidemiology*; D015331:Cohort Studies; D015897:Comorbidity; D016001:Confidence Intervals; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006828:Hydatidiform Mole / Q000175:diagnosis / Q000453:epidemiology* / Q000601:surgery; D015994:Incidence; D011247:Pregnancy; D012042:Registries; D018570:Risk Assessment; D013548:Sweden / Q000453:epidemiology; D014594:Uterine Neoplasms / Q000175:diagnosis / Q000453:epidemiology* / Q000601:surgery