Breast Cancer Risk After Recent Childbirth: A Pooled Analysis of 15 Prospective Studies
Year: 2018
Type: article
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. \n \n Objective: To characterize breast cancer risk in relation to recent childbirth. \n \n Design : Pooled analysis of individual-level data from 15 prospective cohort studies. \n \n Setting: The international Premenopausal Breast Cancer Collaborative Group. \n \n Participants: Women younger than 55 years. \n \n 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. \n \n 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. \n \n 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. \n \n 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. \n \n 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.
DOI: 10.7326/m18-1323
Authors: Nichols, Hazel B, Schoemaker, Minouk J, Cai, Jianwen, Xu, Jiawei, Wright, Lauren B, Brook, Mark N, Jones, Michael E, Adami, Hans-Olov, Baglietto, Laura, Bertrand, Kimberly A, Blot, William J, Boutron-Ruault, Marie-Christine, Dorronsoro, Miren, Dossus, Laure, Eliassen, A Heather, Giles, Graham G, Gram, Inger T, Hankinson, Susan E, Hoffman-Bolton, Judy, Kaaks, Rudolf, Key, Timothy J, Kitahara, Cari M, Larsson, Susanna C, Linet, Martha, Merritt, Melissa A, Milne, Roger L, Pala, Valeria, Palmer, Julie R, Peeters, Petra H, Riboli, Elio, Sund, Malin, Tamimi, Rulla M, Tjønneland, Anne, Trichopoulou, Antonia, Ursin, Giske, Vatten, Lars, Visvanathan, Kala, Weiderpass, Elisabete, Wolk, Alicja, Zheng, Wei, Weinberg, Clarice R, Swerdlow, Anthony J, Sandler, Dale P
Institutions: University of North Carolina at Chapel Hill, Institute of Cancer Research, Karolinska Institutet, University of Pisa, Boston University, Vanderbilt University, Vanderbilt-Ingram Cancer Center, Inserm, Institut Gustave Roussy, Centre de recherche en Epidémiologie et Santé des Populations, Biogipuzkoa Health Research Institute, Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública, Centre international de recherche sur le cancer, Brigham and Women's Hospital, Harvard University, The University of Melbourne, Cancer Council Victoria, UiT The Arctic University of Norway, University of Massachusetts Amherst, Johns Hopkins University, German Cancer Research Center, University of Oxford, National Institutes of Health, National Cancer Institute, Imperial College London, University of Southern California, University of Oslo, Cancer Registry of Norway, University Medical Center Utrecht, Umeå University, Danish Cancer Society, Hellenic Health Foundation, Norwegian University of Science and Technology, Johns Hopkins Medicine, National Institute of Environmental Health Sciences
Language: English
Topic: Cancer Risks and Factors
Subfield: Oncology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W4289035535