title: Risk factors for early age at breast cancer onset--the "COSA program" population-based study.
abstract: BACKGROUND
  Breast cancer is the most frequent cancer in women in western countries. A number of risk factors are now known, but the etiology of the disease is not fully understood. The aim of this study was to determine the effects of reproductive, anthropometric and environmental factors on cancer onset.
  
  
  METHODS
  934 women who developed a non-hereditary breast cancer were recruited from different hospitals in the Auvergne region (France) and completed a questionnaire.
  
  
  RESULTS
  The use of oral contraceptives (OC) increased the risk of early cancer development (odds ratio = 1.84, 95% confidence interval = 1.38-2.44). The age at first OC use appeared to be a major factor since the risk decreased when OC use was after the age of 23 years (odds ratio = 0.52, 95% confidence interval = 0.34-0.79). A duration of breast-feeding greater than 26 weeks decreased the risk of early cancer development (odds ratio = 0.62, 95% confidence interval = 0.39-0.97). No overall association was found with anthropometric or lifestyle factors and early age at breast cancer onset.
  
  
  CONCLUSIONS
  OC use, age at first OC use and lactation were significantly associated with an early age at breast cancer onset. Thus, a number of "risk factors" could be considered as "early onset risk factors".
authors.affiliation: Département d'Oncogénétique, Centre Jean Perrin, BP392, 63011 Clermont-Ferrand, France.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Delort
authors.forename: Fabrice
authors.initials: F
authors.lastname: Kwiatkowski
authors.forename: Nasséra
authors.initials: N
authors.lastname: Chalabi
authors.forename: Samir
authors.initials: S
authors.lastname: Satih
authors.forename: Yves-Jean
authors.initials: YJ
authors.lastname: Bignon
authors.forename: Dominique J
authors.initials: DJ
authors.lastname: Bernard-Gallon
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D000886:Anthropometry; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology; D005260:Female; D005602:France / Q000453:epidemiology; D006801:Humans; D008875:Middle Aged; D015999:Multivariate Analysis; D012098:Reproduction; D012307:Risk Factors