title: Breastfeeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers.
abstract: BACKGROUND
  Breastfeeding has been inversely related to breast cancer risk in the general population. Clarifying the role of breastfeeding among women with a BRCA1 or BRCA2 mutation may be helpful for risk assessment and for recommendations regarding prevention. We present an updated analysis of breastfeeding and risk of breast cancer using a large matched sample of BRCA mutation carriers.
  
  
  METHODS
  We conducted a case-control study of 1,665 pairs of women with a deleterious mutation in either BRCA1 (n = 1,243 pairs) or BRCA2 (n = 422 pairs). Breast cancer cases and unaffected controls were matched on year of birth, mutation status, country of residence and parity. Information about reproductive factors, including breastfeeding for each live birth, was collected from a routinely administered questionnaire. Conditional logistic regression was used to estimate the association between ever having breastfed, as well as total duration of breastfeeding, and the risk of breast cancer.
  
  
  RESULTS
  Among BRCA1 mutation carriers, breastfeeding for at least one year was associated with a 32% reduction in risk (OR = 0.68; 95% CI 0.52 to 0.91; P = 0.008); breastfeeding for two or more years conferred a greater reduction in risk (OR = 0.51; 95% CI 0.35 to 0.74). Among BRCA2 mutation carriers, there was no significant association between breastfeeding for at least one year and breast cancer risk (OR = 0.83; 95% CI 0.53 to 1.31; P = 0.43).
  
  
  CONCLUSIONS
  These data extend our previous findings that breastfeeding protects against BRCA1-, but not BRCA2-associated breast cancer. BRCA mutation carriers should be advised of the benefit of breastfeeding in terms of reducing breast cancer risk.
authors.affiliation: steven.narod@wchospital.ca.
authors.forename: Joanne
authors.initials: J
authors.lastname: Kotsopoulos
authors.forename: Jan
authors.initials: J
authors.lastname: Lubinski
authors.forename: Leonardo
authors.initials: L
authors.lastname: Salmena
authors.forename: Henry T
authors.initials: HT
authors.lastname: Lynch
authors.forename: Charmaine
authors.initials: C
authors.lastname: Kim-Sing
authors.forename: William D
authors.initials: WD
authors.lastname: Foulkes
authors.forename: Parviz
authors.initials: P
authors.lastname: Ghadirian
authors.forename: Susan L
authors.initials: SL
authors.lastname: Neuhausen
authors.forename: Rochelle
authors.initials: R
authors.lastname: Demsky
authors.forename: Nadine
authors.initials: N
authors.lastname: Tung
authors.forename: Peter
authors.initials: P
authors.lastname: Ainsworth
authors.forename: Leigha
authors.initials: L
authors.lastname: Senter
authors.forename: Andrea
authors.initials: A
authors.lastname: Eisen
authors.forename: Charis
authors.initials: C
authors.lastname: Eng
authors.forename: Christian
authors.initials: C
authors.lastname: Singer
authors.forename: Ophira
authors.initials: O
authors.lastname: Ginsburg
authors.forename: Joanne
authors.initials: J
authors.lastname: Blum
authors.forename: Tomasz
authors.initials: T
authors.lastname: Huzarski
authors.forename: Aletta
authors.initials: A
authors.lastname: Poll
authors.forename: Ping
authors.initials: P
authors.lastname: Sun
authors.forename: Steven A
authors.initials: SA
authors.lastname: Narod
mesh_terms: D000328:Adult; D019313:BRCA1 Protein / Q000235:genetics*; D024682:BRCA2 Protein / Q000235:genetics*; D001942:Breast Feeding; D001943:Breast Neoplasms / Q000453:epidemiology / Q000235:genetics*; D016022:Case-Control Studies; D005260:Female; D020022:Genetic Predisposition to Disease; D006579:Heterozygote; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D009154:Mutation; D018570:Risk Assessment
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D024682:BRCA2 Protein; C551750:BRCA2 protein, human