Menstrual and reproductive factors in relation to mammographic density: the Study of Women's Health Across the Nation (SWAN).
Menstrual and reproductive factors may increase breast cancer risk through a pathway that includes increased mammographic density. We assessed whether known or suspected menstrual and reproductive breast cancer risk factors were cross-sectionally associated with mammographic density, by measuring area of radiographic density and total breast area on mammograms from 801 participants in the Study of Women's Health Across the Nation (SWAN), a multi-ethnic cohort of pre- and early perimenopausal women. From multivariable linear regression, the following menstrual or reproductive factors were independently associated with percent mammographic density (area of dense breast/breast area): older age at menarche (beta=10.3, P<0.01, for >13 vs. <12 years), premenstrual cravings and bloating (beta=-3.36, P=0.02), younger age at first full-term birth (beta=-8.12, P<0.01 for <or=23 years versus no births), greater number of births (beta=-6.80, P<0.01 for >or=3 births versus no births), and premenopausal status (beta=3.78, P<0.01 versus early perimenopausal). Only number of births remained associated with percent density after adjustment for age, race/ethnicity, study site, body mass index (BMI), and smoking. In addition, stratified analyses revealed that the association with number of births was confined to women within the lowest BMI tertile (beta=-12.2, P<0.01 for >or=3 births versus no births). Our data support a mechanism for parity and breast cancer that involves mammographic density among pre- and early perimenopausal women that may be modified by body size.
Butler
Lesley M
LM
Division of Epidemiology, Department of Public Health Sciences, University of California at Davis, One Shields Avenue, 1616 DaVinci Court, Davis, CA 95616, USA. lmbutler@ucdavis.edu
Gold
Ellen B
EB
Greendale
Gail A
GA
Crandall
Carolyn J
CJ
Modugno
Francesmary
F
Oestreicher
Nina
N
Quesenberry
Charles P
CP
Habel
Laurel A
LA
D000328:Adult; D015992:Body Mass Index; D001940:Breast / Q000033:anatomy & histology / Q000502:physiology; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008327:Mammography; D008593:Menopause; D008875:Middle Aged; D010298:Parity; D011247:Pregnancy; D017584:Reproductive History; D012307:Risk Factors; D016387:Women's Health