title: Reproductive factors and the risk of triple-negative breast cancer in white women and African-American women: a pooled analysis.
abstract: Early age at menarche, nulliparity, late age at first completed pregnancy, and never having breastfed, are established breast cancer risk factors. However, among breast cancer subtypes, it remains unclear whether all of these are risk factors for triple-negative breast cancer (TNBC).
  
  
  
  We evaluated the associations of these reproductive factors with TNBC, in 2658 patients with breast cancer (including 554 with TNBC) and 2448 controls aged 20-64 years, who participated in one of the three population-based case-control studies: the Women's Contraceptive and Reproductive Experiences Study, the Women's Breast Carcinoma in situ Study, or the Women's Learning the Influence of Family and Environment Study. We used multivariable polychotomous unconditional logistic regression methods to conduct case-control comparisons among breast cancer subtypes defined by estrogen receptor, progesterone receptor, and human epidermal growth factor receptor-2 expression status.
  
  
  
  TNBC risk decreased with increasing duration of breastfeeding (Ptrend= 0.006), but age at menarche, age at first completed pregnancy, and nulliparity were not associated with risk of TNBC. Parous women who breastfed for at least one year had a 31% lower risk of TNBC than parous women who had never breastfed (odds ratio, OR = 0.69; 95% confidence interval, CI = 0.50-0.96). The association between breastfeeding and risk of TNBC was modified by age and race. Parous African-American women aged 20-44 years who breastfed for 6 months or longer had an 82% lower risk of TNBC than their counterparts who had never breastfed (OR = 0.18, 95% CI = 0.07-0.46).
  
  
  
  Our data indicate that breastfeeding decreases the risk of TNBC, especially for younger African-American women.
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA. hma@coh.org.
authors.forename: Huiyan
authors.identifier: 0000-0002-3335-4775
authors.initials: H
authors.lastname: Ma
authors.affiliation: Cancer Registry of Norway, Oslo, Norway.|Department of Nutrition, Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
authors.forename: Giske
authors.initials: G
authors.lastname: Ursin
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA.
authors.forename: Xinxin
authors.initials: X
authors.lastname: Xu
authors.affiliation: Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA.
authors.forename: Eunjung
authors.initials: E
authors.lastname: Lee
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA.|Section of Environment and Radiation, International Agency for Research on Cancer, Lyon, France.
authors.forename: Kayo
authors.initials: K
authors.lastname: Togawa
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA.|School of Social Work, University of Southern California, Los Angeles, CA, 90033, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Duan
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA.
authors.forename: Yani
authors.initials: Y
authors.lastname: Lu
authors.affiliation: Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA, 98109, USA.
authors.forename: Kathleen E
authors.initials: KE
authors.lastname: Malone
authors.affiliation: Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA, 30333, USA.
authors.forename: Polly A
authors.initials: PA
authors.lastname: Marchbanks
authors.affiliation: College of Health and Social Services, New Mexico State University, Las Cruces, NM, 88003, USA.
authors.forename: Jill A
authors.initials: JA
authors.lastname: McDonald
authors.affiliation: Karmanos Cancer Institute, Department of Oncology, Wayne State University, Detroit, MI, 48201, USA.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Simon
authors.affiliation: Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA, 30333, USA.
authors.forename: Suzanne G
authors.initials: SG
authors.lastname: Folger
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA.
authors.forename: Jane
authors.initials: J
authors.lastname: Sullivan-Halley
authors.affiliation: Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA.
authors.forename: Dennis M
authors.initials: DM
authors.lastname: Deapen
authors.affiliation: Pathology, Keck School of Medicine, University of Southern California, Los Angeles, CA, 90033, USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Press
authors.affiliation: Department of Population Sciences, Beckman Research Institute, 1500 East Duarte Rd. Duarte, City of Hope, CA, 91010, USA.
authors.forename: Leslie
authors.initials: L
authors.lastname: Bernstein
mesh_terms: D000328:Adult; D001741:Black or African American / Q000706:statistics & numerical data*; D014408:Biomarkers, Tumor; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D016017:Odds Ratio; D011159:Population Surveillance; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D017584:Reproductive History; D018570:Risk Assessment; D012307:Risk Factors; D064726:Triple Negative Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D044465:White People / Q000706:statistics & numerical data*; D055815:Young Adult
chemical_list: D014408:Biomarkers, Tumor; D018719:Erb-b2 Receptor Tyrosine Kinases; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone
keywords: African-American women; Breastfeeding; Luminal A; Reproductive factors; Triple-negative breast cancer; White women