title: Cigarette smoking and postmenopausal breast cancer risk in a prospective cohort.
abstract: BACKGROUND
  The relationship between cigarette smoking and breast cancer risk has been inconsistent, potentially due to modification by other factors or confounding.
  
  
  METHODS
  We examined smoking and breast cancer risk in a prospective cohort of 186 150 female AARP (formerly American Association of Retired Persons) members, ages 50-71 years, who joined the study in 1995-96 by responding to a questionnaire. Through 2006, 7481 breast cancers were diagnosed. Multivariable-adjusted hazard ratios (HRs) were estimated, overall and stratified by breast cancer risk factors, using Cox proportional hazards regression. Multiplicative interactions were evaluated using the likelihood ratio test.
  
  
  RESULTS
  Increased breast cancer risk was associated with current (HR 1.19, 95% confidence interval (CI) 1.10-1.28) and former (HR 1.07, CI 1.01-1.13) smoking. The current smoking association was stronger among women without (HR 1.24, CI 1.15-1.35) as compared to those with a family history of breast cancer (HR 0.94, CI 0.78-1.13) (P-interaction=0.03). The current smoking association was also stronger among those with later (≥ 15 years: HR 1.52, CI 1.20-1.94) as compared with earlier (≥12 years: HR 1.14, CI 1.03-1.27; 13-14 years: HR 1.18, CI 1.05-1.32) ages at menarche (P-interaction=0.03).
  
  
  CONCLUSIONS
  Risk was elevated in smokers, particularly in those without a family history or late menarche. Research into smoking's effects on the genome and breast development may clarify these relationships.
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive, Bethesda, MD 20892, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Nyante
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive, Bethesda, MD 20892, USA.
authors.forename: G L
authors.initials: GL
authors.lastname: Gierach
authors.affiliation: Department of Epidemiology and Biostatistics, University of Maryland School of Public Health, 2234 SPH Building no. 255, College Park, MD 20742, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Dallal
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive, Bethesda, MD 20892, USA.
authors.forename: N D
authors.initials: ND
authors.lastname: Freedman
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive, Bethesda, MD 20892, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Park
authors.affiliation: Department of Research and Evaluation, Kaiser Permanente Southern California, 100 South Los Robles Avenue, 2nd Floor, Pasadena, CA 91101, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Danforth
authors.affiliation: Strategic Issues Research, AARP Research Center, 601 E Street NW, Washington, DC 20049, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Hollenbeck
authors.affiliation: Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Drive, Bethesda, MD 20892, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Brinton
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D017698:Postmenopause; D011446:Prospective Studies; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology*; D014481:United States / Q000453:epidemiology