American Journal of Epidemiology Advance Access originally published online on October 26, 2007
American Journal of Epidemiology 2008 167(2):230-239; doi:10.1093/aje/kwm271
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ORIGINAL CONTRIBUTIONS |
Timing of Menarche and First Full-Term Birth in Relation to Breast Cancer Risk
1 Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA
2 Department of Preventive Medicine, Keck School of Medicine and Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA
3 Division of Reproductive Health, Centers for Disease Control and Prevention, Atlanta, GA
4 Center for Clinical Epidemiology and Biostatistics and Department of Biostatistics and Epidemiology, School of Medicine, University of Pennsylvania, Philadelphia, PA
5 Division of Hematology and Oncology, Karmanos Cancer Institute, Wayne State University, Detroit, MI
6 Department of Pathology, Keck School of Medicine and Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, CA
7 Department of Nutrition, Faculty of Medicine, University of Oslo, Oslo, Norway
8 Department of Obstetrics and Gynecology, Baystate Medical Center, Springfield, MA
9 Retired. Formerly Contraception and Reproductive Branch, Center for Population Research, National Institute of Child Health and Human Development, Bethesda, MD
Correspondence to Dr. Christopher I. Li, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, M4-C308, P.O. Box 19024, Seattle, WA 98109-1024 (e-mail: cili{at}fhcrc.org).
Received for publication April 12, 2007. Accepted for publication August 22, 2007.
Ages at menarche and first birth are established risk factors for breast cancer. The interval between these ages may also affect risk, since the breast is more susceptible to carcinogenic insults during this period than during the parous period. However, few investigators have studied this relation. Using logistic regression, the authors evaluated associations between the timing of reproductive events and breast cancer risk among 4,013 cases and 4,069 controls enrolled in a multicenter, population-based US case-control study of White and African-American women (1994–1998). For White, parous premenopausal and postmenopausal women, those who had an interval of 
16 years between the ages of menarche and first birth had 1.5-fold (95% confidence interval (CI): 1.0, 2.2) and 1.4-fold (95% CI: 1.1, 1.8) increased risks of breast cancer, respectively, in comparison with those who had 
5 years between these ages. Adjusting for age at first birth altered these risk estimates somewhat, to odds ratios of 1.5 (95% CI: 0.8, 2.9) and 1.0 (95% CI: 0.6, 1.5), respectively. These associations were stronger for lobular and hormone-receptor-positive tumors but were absent among premenopausal African-American women. The authors conclude that the interval between age at menarche and age at first birth is associated with the risk of hormonally sensitive types of breast cancer, particularly among White women.
breast neoplasms; histology; menarche; menopause; pregnancy; premenopause; receptors, estrogen; receptors, progesterone
Abbreviations: CARE, Contraceptive and Reproductive Experiences; CI, confidence interval; ER, estrogen receptor; ICD-O, International Classification of Diseases for Oncology; PR, progesterone receptor
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