. Curie,

M. Paris-tech,

. Embrace, . Genepso, . Bcfr, . Hebon, . Genepso et al.,

N. A. Mbt, . Kk, D. Mar, Y. L. Mbt, N. Jlh et al., All authors read and approved the final manuscript. The funders had no role in the design of the study; the collection, analysis, or interpretation of the data; the writing of the manuscript; or the decision to submit the manuscript for publication, We acknowledge the EMBRACE Centres: the Coordinating Centre: University of Cambridge and the Collaborating Centres: Guy's and St. Thomas' NHS Foundation Trust

&. Birmingham-women, Hospital Healthcare NHS Trust

, Addenbrooke's Hospital

. St and . Georges,

R. Devon and E. Hospital, Exeter: Carole Brewer, Sheffield Children's Hospital

, Great Ormond Street Hospital for Children NHS Trust

C. Hospital, :. Oxford, and . Walker, Western General Hospital

, Bristol: Alan Donaldson; Belfast City Hospital

, Alder Hey Hospital

. Kennedy-galton-centre, Harrow: Angela Brady; Trinity College Dublin and St James's Hospital, University Hospitals of Leicester NHS Trust

R. Glan-clwyd-hospital, . Pottinger;-singleton-hospital, :. Swansea, and . Murray, The BCFR wish to thank members and participants in the Breast Cancer Family Registry from the New York, northern California, Ontario, Philadelphia, and Utah sites for their contributions to the study. BCFR-Australia wish to acknowledge Maggie Angelakos, Gillian Dite, and Helen Tsimiklis. The CNIO thanks Alicia Barroso, Rosario Alonso, and Guillermo Pita for their assistance, Catherine Noguès, Emmanuel Breysse, Pauline Pontois, Lilian Laborde, and the Collaborating Centers: Institut Curie

B. Buecher, G. Institut, V. Roussy, and . Caron,

P. Centre and . Strauss,

K. B. Kuchenbaecker, J. L. Hopper, and D. R. Barnes, Risks of breast, ovarian, and contralateral breast cancer for BRCA1 and BRCA2 mutation carriers, JAMA, vol.317, issue.23, pp.2402-2416, 2017.

J. L. Kelsey, M. D. Gammon, and E. M. John, Reproductive factors and breast cancer, Epidemiol Rev, vol.15, issue.1, pp.36-47, 1993.

V. Beral, D. Bull, and R. Doll, Breast cancer and abortion: collaborative reanalysis of data from 53 epidemiological studies, including 83 000 women with breast cancer from 16 countries, Lancet, vol.363, issue.9414, pp.1007-1016, 2004.

J. R. Palmer, L. A. Wise, and L. L. Adams-campbell, A prospective study of induced abortion and breast cancer in African-American women, Cancer Causes Control, vol.15, issue.2, pp.105-111, 2004.

M. Mahue-giangreco, G. Ursin, and J. Sullivan-halley, Induced abortion, miscarriage, and breast cancer risk of young women, Cancer Epidemiol Biomarkers Prev, vol.12, issue.3, pp.209-214, 2003.

M. Lambe, C. Hsieh, and D. Trichopoulos, Transient increase in the risk of breast cancer after giving birth, N Engl J Med, vol.331, issue.1, pp.5-9, 1994.

G. Albrektsen, I. Heuch, and S. Hansen, Breast cancer risk by age at birth, time since birth and time intervals between births: exploring interaction effects, Br J Cancer, vol.92, issue.1, pp.167-175, 2005.

X. Sun, H. B. Nichols, and C. Tse, Association of parity and time since last birth with breast cancer prognosis by intrinsic subtype, Cancer Epidemiology Biomarkers Prev, vol.25, issue.1, pp.60-67, 2016.

M. E. Work, E. M. John, and I. L. Andrulis, Reproductive risk factors and oestrogen/progesterone receptor-negative breast cancer in the Breast Cancer Family Registry, Br J Cancer, vol.110, issue.5, pp.1367-1377, 2014.

V. Beral, D. Bull, and R. Doll, Breast cancer and breastfeeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50 302 women with breast cancer and 96 973 women without the disease, Lancet, vol.360, issue.9328, pp.187-195, 2002.

T. M. Friebel, S. M. Domchek, and T. R. Rebbeck, Modifiers of cancer risk in BRCA1 and BRCA2 mutation carriers: systematic review and meta-analysis, J Natl Cancer Inst, vol.106, issue.6, p.91, 2014.

H. Pan, Z. He, and L. Ling, Reproductive factors and breast cancer risk among BRCA1 or BRCA2 mutation carriers: results from ten studies, Cancer Epidemiol, vol.38, issue.1, pp.1-8, 2014.

A. C. Antoniou, A. Shenton, and E. R. Maher, Parity and breast cancer risk among BRCA1 and BRCA2 mutation carriers, Breast Cancer Res, vol.8, issue.6, p.72, 2006.

E. Lee, H. Ma, and R. Mckean-cowdin, Effect of reproductive factors and oral contraceptives on breast cancer risk in BRCA1/2 mutation carriers and noncarriers: results from a population-based study, Cancer Epidemiol Biomarkers Prev, vol.17, issue.11, pp.3170-3178, 2008.

R. L. Milne, A. Osorio, and T. Ramon-y-cajal, Parity and the risk of breast and ovarian cancer in BRCA1 and BRCA2 mutation carriers, Breast Cancer Res Treat, vol.119, issue.1, pp.221-232, 2010.

C. A. Cullinane, J. Lubinski, and S. L. Neuhausen, Effect of pregnancy as a risk factor for breast cancer in BRCA1/BRCA2 mutation carriers, Int J Cancer, vol.117, issue.6, pp.988-991, 2005.

H. Jernstrom, J. Lubinski, and H. T. Lynch, Breast-feeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers, J Natl Cancer Inst, vol.96, issue.14, pp.1094-1098, 2004.

J. Kotsopoulos, J. Lubinski, and L. Salmena, Breastfeeding and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers, Breast Cancer Res, vol.14, issue.2, p.42, 2012.

N. Andrieu, D. E. Goldgar, and D. F. Easton, Pregnancies, breast-feeding, and breast cancer risk in the International BRCA1/2 Carrier Cohort Study (IBCCS)
URL : https://hal.archives-ouvertes.fr/inserm-00135798

, J Natl Cancer Inst, vol.98, issue.8, pp.535-544, 2006.

D. Goldgar, C. Bonnardel, and H. Renard, The International BRCA1/2 Carrier Cohort Study: purpose, rationale, and study design, Breast Cancer Res, vol.2, issue.6, p.10, 2000.

E. M. John, J. L. Hopper, and J. C. Beck, The Breast Cancer Family Registry: an infrastructure for cooperative multinational, interdisciplinary and translational studies of the genetic epidemiology of breast cancer, Breast Cancer Res, vol.6, issue.4, pp.375-389, 2004.

K. A. Phillips, P. N. Butow, and A. E. Stewart, Predictors of participation in clinical and psychosocial follow-up of the kConFab breast cancer family cohort, Fam Cancer, vol.4, issue.2, pp.105-113, 2005.

H. Thorne, G. Mitchell, and S. Fox, kConFab: a familial breast cancer consortium facilitating research and translational oncology, J Natl Cancer Inst Monogr, vol.2011, issue.43, pp.79-81, 2011.

M. B. Terry, K. A. Phillips, and M. B. Daly, Cohort profile: the Breast Cancer Prospective Family Study Cohort (ProF-SC), Int J Epidemiol, issue.3, pp.683-92

A. C. Antoniou, D. E. Goldgar, and N. Andrieu, A weighted cohort approach for analysing factors modifying disease risks in carriers of high-risk susceptibility genes, Genet Epidemiol, vol.29, issue.1, pp.1-11, 2005.

A. Antoniou, P. D. Pharoah, and S. Narod, Average risks of breast and ovarian cancer associated with BRCA1 or BRCA2 mutations detected in case series unselected for family history: a combined analysis of 22 studies, Am J Hum Genet, vol.72, issue.5, pp.1117-1130, 2003.

G. K. Reeves, K. Pirie, and J. Green, Comparison of the effects of genetic and environmental risk factors on in situ and invasive ductal breast cancer, Int J Cancer, vol.131, issue.4, pp.930-937, 2012.

K. N. Anderson, R. B. Schwab, and M. E. Martinez, Reproductive risk factors and breast cancer subtypes: a review of the literature, Breast Cancer Res Treat, vol.144, issue.1, pp.1-10, 2014.

J. Russo and I. H. Russo, DNA labeling index and structure of the rat mammary gland as determinants of its susceptibility to carcinogenesis, J Natl Cancer Inst, vol.61, issue.6, pp.1451-1459, 1978.

J. Russo, L. K. Tay, and I. H. Russo, Differentiation of the mammary gland and susceptibility to carcinogenesis, Breast Cancer Res Treat, vol.2, issue.1, pp.5-73, 1982.

K. Britt, A. Ashworth, and M. Smalley, Pregnancy and the risk of breast cancer, Endocr Relat Cancer, vol.14, issue.4, pp.907-933, 2007.

G. Dall, G. Risbridger, and K. Britt, Mammary stem cells and parity-induced breast cancer protection -new insights, J Steroid Biochem Mol Biol, vol.170, pp.54-60, 2017.

J. M. Faupel-badger, K. F. Arcaro, and J. J. Balkam, Postpartum remodeling, lactation, and breast cancer risk: summary of a National Cancer Institutesponsored workshop, J Natl Cancer Inst, vol.105, issue.3, pp.166-174, 2013.