title: Association between allergies, asthma, and breast cancer risk among women in Ontario, Canada.
abstract: OBJECTIVE
  To investigate the association between allergies, asthma, and breast cancer risk in a large, population-based case-control study.
  
  
  METHODS
  Breast cancer cases (n = 3,101) were identified using the Ontario Cancer Registry and population controls (n = 3,471) through random digit dialing. Self-reported histories of allergies, hay fever, and asthma were collected by questionnaire. Logistic regression was used to assess associations between breast cancer risk and history of allergy/hay fever and asthma, with 16 possible confounders examined. Analyses were stratified by menopausal status.
  
  
  RESULTS
  A history of allergies or hay fever was associated with a small reduction in breast cancer risk [age-adjusted odds ratio (AOR) = 0.86, 95 % confidence interval (CI) 0.77-0.96] and did not differ by menopausal status. Asthma was not associated with breast cancer risk overall; however, among premenopausal women, asthma was associated with a reduced risk of breast cancer (AOR = 0.72, 95 % CI 0.54-0.97).
  
  
  CONCLUSIONS
  A history of allergies may be associated with a modest reduction in breast cancer risk. Asthma does not appear to be associated with breast cancer risk overall; however, asthma may be associated with reduced breast cancer risk among premenopausal women.
authors: Prevention and Cancer Control, Cancer Care Ontario, 620 University Ave, Toronto, ON, M5G 2L7, Canada. beth.lowcock@cancercare.on.ca
authors: Elizabeth C
authors: EC
authors: Lowcock
authors: Michelle
authors: M
authors: Cotterchio
authors: Noor
authors: N
authors: Ahmad
mesh_terms: D000328:Adult; D000368:Aged; D001249:Asthma / Q000150:complications / Q000453:epidemiology; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology / Q000473:pathology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D006967:Hypersensitivity / Q000150:complications / Q000453:epidemiology*; D016015:Logistic Models; D008875:Middle Aged; D016017:Odds Ratio; D009864:Ontario / Q000453:epidemiology; D018570:Risk Assessment; D011795:Surveys and Questionnaires