title: Combined effect of oral contraceptive use and hormone replacement therapy on breast cancer risk in postmenopausal women.
abstract: OBJECTIVE
  We examined breast cancer risk related to lifetime exposure to oral contraceptives (OCs) and hormone replacement therapy (HRT) in postmenopausal women.
  
  
  METHODS
  The Women's Contraceptive and Reproductive Experiences (CARE) Study was a population-based case-control study that included 1847 postmenopausal women with incident invasive breast cancer, and 1932 control subjects, identified using random digit dialing.
  
  
  RESULTS
  45% of cases and 49% of controls used both OCs and HRT. OC users were not at increased risk regardless of subsequent HRT exposure. HRT users who had used OCs previously did not have a higher risk of breast cancer than women with no exposure to OCs. We observed a negative interaction (p-value: 0.032) of combined hormone replacement therapy (CHRT) and past OC use. The increase in risk with CHRT was stronger in women who had never used OCs in the past (odds ratio: 1.05; 95% confidence interval: 1.01-1.10 per year of exclusive CHRT use) than in women who had used OCs (odds ratio: 1.00; 95% confidence interval: 0.97-1.03).
  
  
  CONCLUSIONS
  We found no indication that adverse effects of exposure to OCs or HRT appeared only in the presence of the other hormone or were exacerbated by exposure to the other hormone.
authors.affiliation: Center for Clinical Epidemiology and Biostatistics, Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, PA 19104-6021, USA. snorman@cceb.med.upenn.edu
authors.forename: Sandra A
authors.initials: SA
authors.lastname: Norman
authors.forename: Jesse A
authors.initials: JA
authors.lastname: Berlin
authors.forename: Anita L
authors.initials: AL
authors.lastname: Weber
authors.forename: Brian L
authors.initials: BL
authors.lastname: Strom
authors.forename: Janet R
authors.initials: JR
authors.lastname: Daling
authors.forename: Linda K
authors.initials: LK
authors.lastname: Weiss
authors.forename: Polly A
authors.initials: PA
authors.lastname: Marchbanks
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
authors.forename: Lynda F
authors.initials: LF
authors.lastname: Voigt
authors.forename: Jill A
authors.initials: JA
authors.lastname: McDonald
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Liff
authors.forename: Ronald T
authors.initials: RT
authors.lastname: Burkman
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: Malone
authors.forename: Michael S
authors.initials: MS
authors.lastname: Simon
authors.forename: Suzanne G
authors.initials: SG
authors.lastname: Folger
authors.forename: Dennis
authors.initials: D
authors.lastname: Deapen
authors.forename: Phyllis A
authors.initials: PA
authors.lastname: Wingo
authors.forename: Robert
authors.initials: R
authors.lastname: Spirtas
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000139:chemically induced* / Q000453:epidemiology; D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D004359:Drug Therapy, Combination; D015914:Estrogen Replacement Therapy / Q000009:adverse effects*; D005260:Female; D005845:Georgia / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008824:Michigan / Q000453:epidemiology; D008875:Middle Aged; D010414:Pennsylvania / Q000453:epidemiology; D017698:Postmenopause; D012307:Risk Factors; D014861:Washington / Q000453:epidemiology; D016387:Women's Health
chemical_list: D003276:Contraceptives, Oral