Investigating the Association of Lactation History and Postmenopausal Breast Cancer Risk in the Women's Health Initiative

Abstract

Prolonged lactation (≥24 mo) has been associated with reduced breast cancer risk. This research examined this association in postmenopausal women in the Women's Health Initiative (WHI) Hormone Trial (HT) and Observational Study (OS). This retrospective cohort analysis included 69,358 predominantly overweight (65.4%), white (83.2%) postmenopausal women without breast cancer. Women in the HT were randomized to 0.625 mg conjugated equine estrogen (CEE), 0.625 CEE + 2.5 mg medroxyprogesterone acetate (CEE/MPA), or placebo. OS participants had no restrictions on hormone use. Lactation history was assessed via WHI Reproductive History Questionnaire. Most women breastfed at least 1 mo (58.0%); 35.4% breastfed 1–2 children; and 6.5% stated having breastfed ≥24mo. Women in the HT–CEE who breastfed their first child between 20–24 yr of age demonstrated a nonsignificant decreased risk of breast cancer (HR: 0.62; 95% CI: 0.38, 1.01). OS participants who reported CEE/MPA hormone use and age of first breastfeeding ≥30 yr showed a significant increased risk of breast cancer (HR: 1.66; 95% CI: 1.14, 2.41). Risk was increased if age of last breastfeeding was ≥35yr (HR: 1.50; 95% CI: 1.05, 2.14). This research did not demonstrate a significantly decreased risk of postmenopausal breast cancer in women who breastfed for ≥24 mo during their lifetime.

ACKNOWLEDGMENTS

The Women's Health Initiative program is funded by the National Heart, Lung, and Blood Institute, National Institutes of Health, U.S. Department of Health and Human Services through contracts HHSN268201100046C, HHSN268201100001C, HH SN268201100002C, HHSN268201100003C, HHSN2682011 00004C, and HHSN271201100004C. The authors would like to acknowledge the following WHI investigators. Program Office: Jacques Rossouw, Shari Ludlam, Dale Burwen, Joan McGowan, Leslie Ford, and Nancy Geller (National Heart, Lung, and Blood Institute, Bethesda, MD). Clinical Coordinating Center: Garnet Anderson, Ross Prentice, Andrea LaCroix, and Charles Kooperberg (Fred Hutchinson Cancer Research Center, Seattle, WA). Investigators and academic centers: JoAnn E. Manson (Brigham and Women's Hospital, Harvard Medical School, Boston, MA); Barbara V. Howard (MedStar Health Research Institute/Howard University, Washington, DC); Marcia L. Stefanick (Stanford Prevention Research Center, Stanford, CA); Rebecca Jackson (The Ohio State University, Columbus, OH); Cynthia A. Thomson (University of Arizona, Tucson/Phoenix, AZ); Jean Wactawski-Wende(University at Buffalo, Buffalo, NY); Marian Limacher (University of Florida, Gainesville/Jacksonville, FL); Robert Wallace (University of Iowa, Iowa City/Davenport, IA); Lewis Kuller (University of Pittsburgh, Pittsburgh, PA); and Sally Shumaker (Wake Forest University School of Medicine, Winston-Salem, NC).