title: Use of exogenous hormones and the risk of breast cancer: results from self-reported survey data with validity assessment.
abstract: OBJECTIVE
  Main aim was to estimate the association between use of exogenous hormones and breast cancer (BC) risk in a large population-based survey, and to assess the representativeness and overall validity of the data.
  
  
  METHODS
  The survey 'Women's Health and Use of Hormones' was conducted in Finland in 2009, including 7,000 BC cases and 20,000 matched population controls. Conditional logistic regression was used to estimate odds ratios and their 95 % confidence interval. For validation, exposure prevalences were compared with population data from Statistics Finland and two large population-based surveys.
  
  
  RESULTS
  We found positive associations with BC risk and exclusive use of hormone-releasing intrauterine device (HR IUD) in postmenopausal women (1.48, 95 % CI 1.10-1.99), when compared to never-users of any hormonal contraceptive and considering only prediagnostic use in cases. Regarding use of other hormonal contraceptives (HC), a positive association between long HC use (≥2 years) and BC was observed in both groups, OR being 1.37 (95 % CI 1.12-1.68) for premenopausal and 1.11 (95 % CI 1.03-1.20) for postmenopausal women, when compared to never-users of other HC.
  
  
  CONCLUSIONS
  Observed association between HR IUD use and risk of BC in postmenopausal women is worrying and deserves further attention. Selection bias seemed not to explain this result. Considering the increasing popularity of HR IUD use in, e.g., USA, impact of possible adverse effects in public health could be significant.
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, 00130, Helsinki, Finland. sanna.heikkinen@cancer.fi.
authors.forename: Sanna
authors.identifier: http://orcid.org/0000-0001-9995-5605
authors.initials: S
authors.lastname: Heikkinen
authors.affiliation: Department of Public Health, Hjelt Institute, University of Helsinki, Mannerheimintie 172, PO Box 41, 00014, Helsinki, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Koskenvuo
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, 00130, Helsinki, Finland.|School of Health Sciences, University of Tampere, 33014, Tampere, Finland.
authors.forename: Nea
authors.initials: N
authors.lastname: Malila
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, 00130, Helsinki, Finland.
authors.forename: Tytti
authors.initials: T
authors.lastname: Sarkeala
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, 00130, Helsinki, Finland.|School of Health Sciences, University of Tampere, 33014, Tampere, Finland.
authors.forename: Eero
authors.initials: E
authors.lastname: Pukkala
authors.affiliation: Finnish Cancer Registry, Institute for Statistical and Epidemiological Cancer Research, Unioninkatu 22, 00130, Helsinki, Finland.|Department of Public Health, Hjelt Institute, University of Helsinki, Mannerheimintie 172, PO Box 41, 00014, Helsinki, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Pitkäniemi
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology*; D003271:Contraceptive Agents, Female / Q000627:therapeutic use; D003278:Contraceptives, Oral, Hormonal / Q000627:therapeutic use*; D004343:Drug Implants; D015914:Estrogen Replacement Therapy / Q000706:statistics & numerical data*; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D007436:Intrauterine Devices, Medicated / Q000706:statistics & numerical data*; D016015:Logistic Models; D008875:Middle Aged; D016017:Odds Ratio; D017698:Postmenopause; D017697:Premenopause; D015995:Prevalence; D015203:Reproducibility of Results; D017584:Reproductive History; D012307:Risk Factors; D057566:Self Report; D057968:Transdermal Patch; D055815:Young Adult
chemical_list: D003271:Contraceptive Agents, Female; D003278:Contraceptives, Oral, Hormonal; D004343:Drug Implants
keywords: Breast cancer; Case–control study; Epidemiology; Hormonal contraceptives; Intrauterine device