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Breast Cancer Res Treat. 2016 Jul;158(2):351-9. doi: 10.1007/s10549-016-3884-y. Epub 2016 Jun 28.

Reproductive factors related to childbearing and mammographic breast density.

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Department of Epidemiology, College of Public Health and Health Professions and College of Medicine, University of Florida, 2004 Mowry Road, Room 4216, Box 100231, Gainesville, FL, 32610-0231, USA.
Department of Surgery, Washington University in St. Louis School of Medicine, 660 S. Euclid Ave., St. Louis, MO, 63110, USA.
Institute for Public Health, Washington University in St. Louis, St. Louis, MO, USA.
Channing Division of Network Medicine, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA, 02115, USA.
Slone Epidemiology Center at Boston University, 1010 Commonwealth Avenue, Boston, MA, 02215, USA.


We investigated the associations of reproductive factors related to childbearing with percent breast density, absolute dense and nondense areas, by menopausal status. This study included 4110 cancer-free women within the Nurses' Health Study and Nurses' Health Study II cohorts. Percent breast density, absolute dense and nondense areas were measured from digitized mammography film images with computerized techniques. All density measures were square root-transformed in all the analyses to improve normality. The data on reproductive variables and other breast cancer risk factors were obtained from biennial questionnaires, at the time of the mammogram date. As compared to nulliparous women, parous postmenopausal women had lower percent density (β = -0.60, 95 % CI -0.84; -0.37), smaller absolute dense area (β = -0.66, 95 % CI -1.03; -0.29), and greater nondense area (β = 0.72, 95 % CI 0.27; 1.16). Among parous women, number of children was inversely associated with percent density in pre- (β per one child = -0.12, 95 % CI -0.20; -0.05) and postmenopausal women (β per one child = -0.07, 95 % CI -0.12; -0.02). The positive associations of breastfeeding with absolute dense and nondense areas were limited to premenopausal women, while the positive association of the age at first child's birth with percent density and the inverse association with nondense area were limited to postmenopausal women. Women with greater number of children and younger age at first child's birth have more favorable breast density patterns that could explain subsequent breast cancer risk reduction.


Age at first child; Breast density; Breastfeeding; Parity; Risk prediction

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