title: Oral contraceptive formulation and risk of breast cancer.
abstract: BACKGROUND
  While evidence on the association between oral contraceptive (OC) use and breast cancer generally suggests little or no increased risk, the question of whether breast cancer risk varies by OC formulation remains controversial. Few studies have examined this issue because large samples and extensive OC histories are required.
  
  
  METHODS
  We used data from a multicenter, population-based, case-control investigation. Women aged 35-64 years were interviewed. To explore the association between OC formulation and breast cancer risk, we used conditional logistic regression to derive adjusted odds ratios, and we used likelihood ratio tests for heterogeneity to assess whether breast cancer risk varied by OC formulation. Key OC exposure variables were ever use, current or former use, duration of use and time since last use. To strengthen inferences about specific formulations, we restricted most analyses to the 2282 women with breast cancer and the 2424 women without breast cancer who reported no OC use or exclusive use of one OC.
  
  
  RESULTS
  Thirty-eight formulations were reported by the 2674 women who used one OC; most OC formulations were used by only a few women. We conducted multivariable analyses on the 10 formulations that were each used by at least 50 women and conducted supplemental analyses on selected formulations of interest based on recent research. Breast cancer risk did not vary significantly by OC formulation, and no formulation was associated with a significantly increased breast cancer risk.
  
  
  CONCLUSIONS
  These results add to the small body of literature on the relationship between OC formulation and breast cancer. Our data are reassuring in that, among women 35-64 years of age, we found no evidence that specific OC formulations increase breast cancer risk.
authors: Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. pam2@cdc.gov
authors: Polly A
authors: PA
authors: Marchbanks
authors: Kathryn M
authors: KM
authors: Curtis
authors: Michele G
authors: MG
authors: Mandel
authors: Hoyt G
authors: HG
authors: Wilson
authors: Gary
authors: G
authors: Jeng
authors: Suzanne G
authors: SG
authors: Folger
authors: Jill A
authors: JA
authors: McDonald
authors: Janet R
authors: JR
authors: Daling
authors: Leslie
authors: L
authors: Bernstein
authors: Kathleen E
authors: KE
authors: Malone
authors: Phyllis A
authors: PA
authors: Wingo
authors: Michael S
authors: MS
authors: Simon
authors: Sandra A
authors: SA
authors: Norman
authors: Brian L
authors: BL
authors: Strom
authors: Giske
authors: G
authors: Ursin
authors: Linda K
authors: LK
authors: Weiss
authors: Ronald T
authors: RT
authors: Burkman
authors: Robert
authors: R
authors: Spirtas
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000139:chemically induced*; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D003278:Contraceptives, Oral, Hormonal / Q000009:adverse effects*; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D008875:Middle Aged; D012306:Risk; D011795:Surveys and Questionnaires
chemical_list: D003276:Contraceptives, Oral; D003278:Contraceptives, Oral, Hormonal