@article{a5c8a703ce1f4a049f89d07b72a7b346,
title = "Breast cancer risk after recent childbirth: A pooled analysis of 15 prospective studies",
abstract = "Background: Parity is widely recognized as protective for breast cancer, but breast cancer risk may be increased shortly after childbirth. Whether this risk varies with breastfeeding, family history of breast cancer, or specific tumor subtype has rarely been evaluated. Objective: To characterize breast cancer risk in relation to recent childbirth. Design: Pooled analysis of individual-level data from 15 prospective cohort studies. Setting: The international Premenopausal Breast Cancer Collaborative Group. Participants: Women younger than 55 years. Measurements: During 9.6 million person-years of follow-up, 18 826 incident cases of breast cancer were diagnosed. Hazard ratios (HRs) and 95% CIs for breast cancer were calculated using Cox proportional hazards regression. Results: Compared with nulliparous women, parous women had an HR for breast cancer that peaked about 5 years after birth (HR, 1.80 [95% CI, 1.63 to 1.99]) before decreasing to 0.77 (CI, 0.67 to 0.88) after 34 years. The association crossed over from positive to negative about 24 years after birth. The overall pattern was driven by estrogen receptor (ER)-positive breast cancer; no crossover was seen for ER-negative cancer. Increases in breast cancer risk after childbirth were pronounced when combined with a family history of breast cancer and were greater for women who were older at first birth or who had more births. Breastfeeding did not modify overall risk patterns. Limitations: Breast cancer diagnoses during pregnancy were not uniformly distinguishable from early postpartum diagnoses. Data on human epidermal growth factor receptor 2 (HER2) oncogene overexpression were limited. Conclusion: Compared with nulliparous women, parous women have an increased risk for breast cancer for more than 20 years after childbirth. Health care providers should consider recent childbirth a risk factor for breast cancer in young women.",
keywords = "Adolescent, Adult, Breast Feeding, Breast Neoplasms/diagnosis, Female, Genetic Predisposition to Disease, Humans, Maternal Age, Middle Aged, Parity, Parturition, Pregnancy, Premenopause, Proportional Hazards Models, Prospective Studies, Receptors, Estrogen/analysis, Risk Factors, Young Adult",
author = "Nichols, {Hazel B.} and Schoemaker, {Minouk J.} and Jianwen Cai and Jiawei Xu and Wright, {Lauren B.} and Brook, {Mark N.} and Jones, {Michael E.} and Adami, {Hans Olov} and Laura Baglietto and Bertrand, {Kimberly A.} and Blot, {William J.} and Boutron-Ruault, {Marie Christine} and Miren Dorronsoro and Laure Dossus and Eliassen, {A. Heather} and Giles, {Graham G.} and Gram, {Inger T.} and Hankinson, {Susan E.} and Judy Hoffman-Bolton and Rudolf Kaaks and Key, {Timothy J.} and Kitahara, {Cari M.} and Larsson, {Susanna C.} and Martha Linet and Merritt, {Melissa A.} and Milne, {Roger L.} and Valeria Pala and Palmer, {Julie R.} and Peeters, {Petra H.} and Elio Riboli and Malin Sund and Tamimi, {Rulla M.} and Anne Tj{\o}nneland and Antonia Trichopoulou and Giske Ursin and Lars Vatten and Kala Visvanathan and Elisabete Weiderpass and Alicja Wolk and Wei Zheng and Weinberg, {Clarice R.} and Swerdlow, {Anthony J.} and Sandler, {Dale P.}",
note = "Funding Information: Disclosures: Dr. Schoemaker reports grants from the United Kingdom– based charity Breast Cancer Now during the conduct of the study. Dr. Cai reports grants from the Avon Foundation during the conduct of the study. Ms. Wright reports grants from Breast Cancer Now during the conduct of the study. Dr. Jones reports grants from Breast Cancer Now during the conduct of the study. Dr. Giles reports grants from the National Health and Medical Research Council during the conduct of the study. Dr. Key reports grants from Cancer Research UK during the conduct of the study. Dr. Milne reports grants from the Australian National Health and Medical Research Council during the conduct of the study. Dr. Swerdlow reports grants from Breast Cancer Now during the conduct of the study. Authors not named here have disclosed no conflicts of interest. Disclosures can also be viewed at www.acponline.org/authors/icmje/Conflict OfInterestForms.do?msNum=M18-1323. Funding Information: In part by the Avon Foundation (02-2014-080); funding from Breast Cancer Now and the U.K. National Health Service to the Royal Marsden-Institute of Cancer Research National Institute for Health Research Biomedical Research Centre; the Institute of Cancer Research, London; the National Institute of Environmental Health Sciences (Z01 ES044005) and National Cancer Institute (UM1 CA176726, UM1 CA186107, UM1 CA164974, R01 CA058420, R01 CA092447, and P50 CA168504) of the National Institutes of Health; the National Center for Advancing Translational Sciences (KL2-TR001109); the National Program of Cancer Registries of the Centers for Disease Control and Prevention and the Department of Energy; the Swedish Research Council and Swedish Cancer Society; the Japanese Ministry of Health, Labour and Welfare; the Hellenic Health Foundation; a Karolinska Institutet Distinguished Professor Award (2368/10-221); Cancer Council Victoria and the Australia National Health and Medical Research Council (209057, 396414, and 504711); the state of Maryland; and the Maryland Cigarette Restitution Fund. The coordination of EPIC (the European Prospective Investigation into Cancer and Nutrition) is financially supported by the European Commission (DG-SANCO) and the International Agency for Research on Cancer. The national cohorts are supported by the Danish Cancer Society (Denmark); Ligue Contre le Cancer, Institut Gustave Roussy, Mutuelle G{\'e}n{\'e} rale de l'Education Nationale, and Institut National de la Sant{\'e} et de la Recherche M{\'e} dicale (France); German Cancer Aid, German Cancer Research Center, and Federal Ministry of Education and Research (Germany); the Hellenic Health Foundation (Greece); Associazione Italiana per la Ricerca sul Cancro and National Research Council (Italy); Dutch Ministry of Public Health, Welfare and Sport, Netherlands Cancer Registry, LK Research Funds, Dutch Prevention Funds, Zorg Onderzoek Nederland, World Cancer Research Fund, and Statistics Netherlands (the Netherlands); ERC-2009-AdG 232997, Health Research Fund (FIS), PI13/00061 to Granada, PI13/01162 to EPIC-Murcia, regional governments of Andaluc{\'i}a, Asturias, Basque Country, Murcia, and Navarra, and ISCIII RETIC (RD06/0020) (Spain); Swedish Cancer Society, Swedish Research Council, and county councils of Sk{\aa}ne and V{\"a} sterbotten (Sweden); and Cancer Research UK (14136 to EPIC-Norfolk and C570/A16491 and C8221/A19170 to EPIC-Oxford) and the Medical Research Council (1000143 to EPIC-Norfolk and MR/M012190/1 to EPIC-Oxford) (United Kingdom). Funding Information: Financial Support: In part by the Avon Foundation (02-2014-080); funding from Breast Cancer Now and the U.K. National Health Service to the Royal Marsden–Institute of Cancer Research National Institute for Health Research Biomedical Research Centre; the Institute of Cancer Research, London; the National Institute of Environmental Health Sciences (Z01 ES044005) and National Cancer Institute (UM1 CA176726, UM1 CA186107, UM1 CA164974, R01 CA058420, R01 CA092447, and P50 CA168504) of the National Institutes of Health; the National Center for Advancing Translational Sciences (KL2-TR001109); the National Program of Cancer Registries of the Centers for Disease Control and Prevention and the Department of Energy; the Swedish Research Council and Swedish Cancer Society; the Japanese Ministry of Health, Labour and Welfare; the Hellenic Health Foundation; a Karolin-ska Institutet Distinguished Professor Award (2368/10-221); Cancer Council Victoria and the Australia National Health and Medical Research Council (209057, 396414, and 504711); the state of Maryland; and the Maryland Cigarette Restitution Fund. The coordination of EPIC (the European Prospective Investigation into Cancer and Nutrition) is financially supported by the European Commission (DG-SANCO) and the International Agency for Research on Cancer. The national cohorts are supported by the Danish Cancer Society (Denmark); Ligue Contre le Cancer, Institut Gustave Roussy, Mutuelle G{\'e}-n{\'e}rale de l{\textquoteright}Education Nationale, and Institut National de la Sant{\'e} et de la Recherche M{\'e}dicale (France); German Cancer Aid, German Cancer Research Center, and Federal Ministry of Education and Research (Germany); the Hellenic Health Foundation (Greece); Associazione Italiana per la Ricerca sul Can-cro and National Research Council (Italy); Dutch Ministry of Public Health, Welfare and Sport, Netherlands Cancer Registry, LK Research Funds, Dutch Prevention Funds, Zorg Onder-zoek Nederland, World Cancer Research Fund, and Statistics Netherlands (the Netherlands); ERC-2009-AdG 232997, Health Research Fund (FIS), PI13/00061 to Granada, PI13/01162 to EPIC-Murcia, regional governments of Andaluc{\'i}a, Asturias, Basque Country, Murcia, and Navarra, and ISCIII RETIC (RD06/ 0020) (Spain); Swedish Cancer Society, Swedish Research Council, and county councils of Sk{\aa}ne and V{\"a}sterbotten (Sweden); and Cancer Research UK (14136 to EPIC-Norfolk and C570/ A16491 and C8221/A19170 to EPIC-Oxford) and the Medical Research Council (1000143 to EPIC-Norfolk and MR/M012190/1 to EPIC-Oxford) (United Kingdom). Funding Information: Primary Funding Source: The Avon Foundation, the National Institute of Environmental Health Sciences, Breast Cancer Now and the UK National Health Service, and the Institute of Cancer Research. Publisher Copyright: {\textcopyright} 2019 American College of Physicians.",
year = "2019",
month = jan,
day = "1",
doi = "10.7326/M18-1323",
language = "English",
volume = "170",
pages = "22--30",
journal = "Annals of Internal Medicine",
issn = "0003-4819",
publisher = "American College of Physicians",
number = "1",
}