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Breastfeeding and Endometrial Cancer Risk: An Analysis From the Epidemiology of Endometrial Cancer Consortium

Jordan, Susan J. MBBS, PhD; Na, Renhua PhD; Johnatty, Sharon E. PhD; Wise, Lauren A. PhD; Adami, Hans Olov MD, PhD; Brinton, Louise A. PhD, MPH; Chen, Chu PhD; Cook, Linda S. PhD; Dal Maso, Luigino PhD; De Vivo, Immaculata PhD, MPH; Freudenheim, Jo L. PhD, MS; Friedenreich, Christine M. PhD, MSc; La Vecchia, Carlo MD, MSc; McCann, Susan E. PhD, RD; Moysich, Kirsten B. PhD, MS; Lu, Lingeng PhD, MD; Olson, Sara H. PhD; Palmer, Julie R. ScD, MPH; Petruzella, Stacey MPH; Pike, Malcolm C. PhD; Rebbeck, Timothy R. PhD; Ricceri, Fulvio PhD; Risch, Harvey A. MD, PhD; Sacerdote, Carlotta PhD; Setiawan, Veronica Wendy PhD; Sponholtz, Todd R. PhD; Shu, Xiao Ou MD, PhD; Spurdle, Amanda B. PhD; Weiderpass, Elisabete MD, PhD; Wentzensen, Nicolas MD, PhD; Yang, Hannah P. ScM, PhD; Yu, Herbert MD, PhD; Webb, Penelope M. MA, DPhil

doi: 10.1097/AOG.0000000000002057
Contents: Original Research

OBJECTIVE: To investigate the association between breastfeeding and endometrial cancer risk using pooled data from 17 studies participating in the Epidemiology of Endometrial Cancer Consortium.

METHODS: We conducted a meta-analysis with individual-level data from three cohort and 14 case–control studies. Study-specific odds ratios (ORs) and 95% confidence intervals (CIs) were estimated for the association between breastfeeding and risk of endometrial cancer using multivariable logistic regression and pooled using random-effects meta-analysis. We investigated between-study heterogeneity with I 2 and Q statistics and metaregression.

RESULTS: After excluding nulliparous women, the analyses included 8,981 women with endometrial cancer and 17,241 women in a control group. Ever breastfeeding was associated with an 11% reduction in risk of endometrial cancer (pooled OR 0.89, 95% CI 0.81–0.98). Longer average duration of breastfeeding per child was associated with lower risk of endometrial cancer, although there appeared to be some leveling of this effect beyond 6–9 months. The association with ever breastfeeding was not explained by greater parity and did not vary notably by body mass index or histologic subtype (grouped as endometrioid and mucinous compared with serous and clear cell).

CONCLUSION: Our findings suggest that reducing endometrial cancer risk can be added to the list of maternal benefits associated with breastfeeding. Ongoing promotion, support, and facilitation of this safe and beneficial behavior might therefore contribute to the prevention of this increasingly common cancer.

Results from an individual-level data meta-analysis show that breastfeeding is associated with a reduced risk of endometrial cancer.

QIMR Berghofer Medical Research Institute, and the University of Queensland, School of Public Health, Brisbane, Australia; the Department of Epidemiology, Boston University School of Public Health, Boston, Massachusetts; the Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden; the Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, Maryland; the Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington; the Department of Internal Medicine and UNM Comprehensive Cancer Center, University of New Mexico, Albuquerque, New Mexico; the Department of Cancer Epidemiology and Prevention Research, CancerControl Alberta, Alberta Health Services, Calgary, Alberta, Canada; the Unit of Cancer Epidemiology, CRO Aviano, National Cancer Institute, IRCCS, Aviano, Italy; Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts; the Department of Epidemiology and Environmental Health, University at Buffalo, Buffalo, New York; the Department of Clinical Sciences and Community Health, Università degli Studi di Milano, Milano, Italy; Cancer Prevention and Control, Roswell Park Cancer Institute, Buffalo, New York; Yale School of Public Health, New Haven, Connecticut; the Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York, New York; Slone Epidemiology Center, Boston University, Boston, Massachusetts; the Department of Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California; Harvard TH Chan School of Public Health and Dana Farber Cancer Institute, Boston, Massachusetts; the Unit of Cancer Epidemiology, Città della Salute e della Scienza University–Hospital and Center for Cancer Prevention (CPO), Turin, Italy; the Division of Epidemiology, Department of Medicine, Vanderbilt Epidemiology Center, Vanderbilt-Ingram Cancer Centre, Vanderbilt University School of Medicine, Nashville, Tennessee; the Cancer Registry of Norway, Institute of Population-Based Cancer Research, Oslo, Norway; the Genetic Epidemiology Group, Folkhälsan Research Center, Helsinki, Finland; the Department of Community Medicine, University of Tromsø, and the Arctic University of Norway, Tromsø, Norway; and the Epidemiology Program, University of Hawaii Cancer Center, Honolulu, Hawaii.

Corresponding author: Susan J. Jordan, MBBS, PhD, QIMR Berghofer MRI, Locked Bag 2000, PO Royal Brisbane Hospital, Herston 4029, Queensland, Australia; email:

The Alberta Case-Control Study on Endometrial Cancer was funded by The Canadian Cancer Society. C. Friedenreich received career awards from the Canadian Institutes of Health Research and the Alberta Heritage Foundation for Medical Research (AHFMR) during the conduct of this study. L. Cook held a Canada Research Chair and also received career award funding from AHFMR. The Australian National Endometrial Cancer Study was funded by the National Health and Medical Research Council (NHMRC) of Australia (#339435) and Cancer Council Tasmania (#403031 and 457636). S. Jordan, A. Spurdle, and P. Webb are supported by fellowships from the NHMRC of Australia. The National Cancer Institute/National Institutes of Health funded The Black Women's Health Study (grant numbers: R01-CA058420, UMI-CA164974, and R03-CA169888), The Connecticut Endometrial Cancer Study (R01CA098346), The Estrogen, Diet, Genetics, and Endometrial Cancer (R01 CA83918, P30 CA008748), and The Fred Hutchinson Cancer Research Center (R35 CA39779, R01 CA47749, R01 CA75977, N01 HD 2 3166, K05 CA 92002, RO1 CA105212, and R01 CA87538), The Nurses' Health Study (2R01 CA082838), The Polish Endometrial Cancer Study, U.S. Endometrial Cancer Study (in part by intramural funds), The Shanghai Endometrial Cancer Study (R01 CA092585), The USC LA case control study (R01 CA48774 and P30 CA14089), and the Women's Insight and Shared Experience (P01-CA77596). The Italian Multi Centre Study was funded by The Italian Association for Cancer Research (AIRC). C. LaVecchia was supported by the Italian Foundation for Research in Cancer. The Swedish Women's Lifestyle and Health Study was funded by The Swedish Research Council (521-2011-2955). The Turin Case Control Study: The Italian Association for Cancer Research (AIRC) and the Ricerca Finalizzata Regione Piemonte.

Financial Disclosure The authors did not report any potential conflicts of interest.

Each author has indicated that he or she has met the journal’s requirements for authorship.

© 2017 by The American College of Obstetricians and Gynecologists. Published by Wolters Kluwer Health, Inc. All rights reserved.