title: Reproductive risk factors and oestrogen/progesterone receptor-negative breast cancer in the Breast Cancer Family Registry.
abstract: BACKGROUND
  Oestrogen receptor (ER)- and progesterone receptor (PR)-negative (ER-PR-) breast cancer is associated with poorer prognosis compared with other breast cancer subtypes. High parity has been associated with an increased risk of ER-PR- cancer, but emerging evidence suggests that breastfeeding may reduce this risk. Whether this potential breastfeeding benefit extends to women at high risk of breast cancer remains critical to understand for prevention.
  
  
  METHODS
  Using population-based ascertained cases (n=4011) and controls (2997) from the Breast Cancer Family Registry, we examined reproductive risk factors in relation to ER and PR status.
  
  
  RESULTS
  High parity (≥3 live births) without breastfeeding was positively associated only with ER-PR- tumours (odds ratio (OR)=1.57, 95% confidence interval (CI), 1.10-2.24); there was no association with parity in women who breastfed (OR=0.93, 95% CI 0.71-1.22). Across all race/ethnicities, associations for ER-PR- cancer were higher among women who did not breastfeed than among women who did. Oral contraceptive (OC) use before 1975 was associated with an increased risk of ER-PR- cancer only (OR=1.32, 95% CI 1.04-1.67). For women who began OC use in 1975 or later there was no increased risk.
  
  
  CONCLUSIONS
  Our findings support that there are modifiable factors for ER-PR- breast cancer and that breastfeeding in particular may mitigate the increased risk of ER-PR- cancers seen from multiparity.
authors.affiliation: Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 West 168th Street, New York, NY 10032, USA.
authors.forename: M E
authors.initials: ME
authors.lastname: Work
authors.affiliation: 1] Cancer Prevention Institute of California, Fremont, CA 94538, USA [2] Division of Epidemiology, Department of Health Research and Policy, and Stanford Cancer Institute, Stanford University School of Medicine, Stanford, CA 94305-5101, USA.
authors.forename: E M
authors.initials: EM
authors.lastname: John
authors.affiliation: Department of Molecular Genetics, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada M5G 1X5.
authors.forename: I L
authors.initials: IL
authors.lastname: Andrulis
authors.affiliation: 1] Department of Molecular Genetics, Samuel Lunenfeld Research Institute, Mount Sinai Hospital, University of Toronto, Toronto, Ontario, Canada M5G 1X5 [2] Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada M5T 3M7.
authors.forename: J A
authors.initials: JA
authors.lastname: Knight
authors.affiliation: Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 West 168th Street, New York, NY 10032, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Liao
authors.affiliation: 1] Laboratory Medicine Program, University Health Network, Toronto, Ontario, Canada M5G 1X5 [2] Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada M5G 1X5.
authors.forename: A M
authors.initials: AM
authors.lastname: Mulligan
authors.affiliation: Department of Pathology, The University of Melbourne, Melbourne, VIC 3010, Australia.
authors.forename: M C
authors.initials: MC
authors.lastname: Southey
authors.affiliation: 1] Cancer Epidemiology Centre, Cancer Council Victoria, Carlton, VIC 3053, Australia [2] Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, VIC 3010, Australia.
authors.forename: G G
authors.initials: GG
authors.lastname: Giles
authors.affiliation: Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, VIC 3010, Australia.
authors.forename: G S
authors.initials: GS
authors.lastname: Dite
authors.affiliation: Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, VIC 3010, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Apicella
authors.affiliation: Department of Epidemiology and Institute of Health and Environment, School of Public Health, Seoul National University, 110-799 Seoul, Korea.
authors.forename: H
authors.initials: H
authors.lastname: Hibshoosh
authors.affiliation: 1] Centre for Molecular, Environmental, Genetic and Analytic Epidemiology, University of Melbourne, Melbourne, VIC 3010, Australia [2] Department of Epidemiology and Institute of Health and Environment, School of Public Health, Seoul National University, 110-799 Seoul, Korea.
authors.forename: J L
authors.initials: JL
authors.lastname: Hopper
authors.affiliation: 1] Department of Epidemiology, Mailman School of Public Health, Columbia University, 722 West 168th Street, New York, NY 10032, USA [2] Herbert Irving Comprehensive Cancer Center, Columbia University, New York, NY 10032, USA.
authors.forename: M B
authors.initials: MB
authors.lastname: Terry
mesh_terms: D000328:Adult; D001315:Australia / Q000453:epidemiology; D001942:Breast Feeding / Q000706:statistics & numerical data; D001943:Breast Neoplasms / Q000453:epidemiology / Q000235:genetics / Q000378:metabolism*; D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000008:administration & dosage; D005260:Female; D006801:Humans; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D011960:Receptors, Estrogen / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D011980:Receptors, Progesterone / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D012042:Registries; D012098:Reproduction / Q000502:physiology*; D012307:Risk Factors
chemical_list: D003276:Contraceptives, Oral; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone