title: Risk factors for young-onset invasive and in situ breast cancer.
abstract: OBJECTIVE
  Young-onset breast cancers tend to be more aggressive than later-onset tumors and may have different risk factor profiles. Among young-onset cases, there may also be etiologic differences between ductal carcinomas in situ (DCIS) and invasive breast cancer, particularly if some factors promote malignant transformation.
  
  
  METHODS
  We evaluated the association between several potential risk factors and young-onset breast cancer in the Two Sister Study (2008-2010), a sister-matched case-control study involving 1,406 women diagnosed with breast cancer before age 50 (1,185 invasive, 221 DCIS) and 1,648 controls.
  
  
  RESULTS
  Older age at menarche, younger age at menopause, premenopausal hysterectomy, early age at first-term pregnancy, obesity, and consumption of alcohol were associated with reduced risk of young-onset breast cancer. These patterns remained when we limited analysis to invasive breast cancers. In general, effect estimates were similar for young-onset invasive breast cancer and DCIS, although the number of DCIS cases was small.
  
  
  CONCLUSIONS
  In this sister-matched case-control study of young-onset breast cancer, many of the studied risk factors were associated with young-onset invasive breast cancer. There were few discernable differences in risk factors for young-onset DCIS versus young-onset invasive breast cancer.
authors.affiliation: Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences, 111 TW Alexander Dr., Research Triangle Park, NC, 27709, USA.
authors.forename: Katie M
authors.initials: KM
authors.lastname: O'Brien
authors.affiliation: Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences, 111 TW Alexander Dr., Research Triangle Park, NC, 27709, USA.
authors.forename: Jenny
authors.initials: J
authors.lastname: Sun
authors.affiliation: Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.
authors.forename: Dale P
authors.initials: DP
authors.lastname: Sandler
authors.affiliation: Epidemiology Branch, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.|Department of Global Public Health and Primary Care, University of Bergen, Bergen, Norway.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: DeRoo
authors.affiliation: Biostatistics and Computational Biology Branch, National Institute of Environmental Health Sciences, 111 TW Alexander Dr., Research Triangle Park, NC, 27709, USA. weinberg@niehs.nih.gov.
authors.forename: Clarice R
authors.initials: CR
authors.lastname: Weinberg
mesh_terms: D000328:Adult; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology; D002285:Carcinoma, Intraductal, Noninfiltrating / Q000453:epidemiology* / Q000209:etiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008572:Menarche / Q000502:physiology; D008593:Menopause / Q000502:physiology; D008875:Middle Aged; D011247:Pregnancy; D017697:Premenopause; D012307:Risk Factors
keywords: Breast cancer; Ductal carcinoma in situ; Etiologic heterogeneity; Young-onset breast cancer