American Journal of Epidemiology Advance Access originally published online on July 10, 2008
American Journal of Epidemiology 2008 168(4):412-421; doi:10.1093/aje/kwn169
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ORIGINAL CONTRIBUTIONS |
Ethnic Variations in Mammographic Density: A British Multiethnic Longitudinal Study
1 Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, United Kingdom
2 Breast Assessment Centre, St. Bartholomew's Hospital, London, United Kingdom
Correspondence to Dr. Valerie McCormack, Department of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, United Kingdom (e-mail: Valerie.mccormack{at}lshtm.ac.uk).
Received for publication January 17, 2008. Accepted for publication May 14, 2008.
It is not known whether the 20–30% lower breast cancer incidence rates in first-generation South Asian and Afro-Caribbean women relative to Caucasian women in the United Kingdom are reflected in mammographic density. The authors conducted a United Kingdom population-based multiethnic study of mammographic density at ages 50–64 years in 645 women. Data on breast cancer risk factors were obtained using a questionnaire/telephone interview. Threshold percent density was assessed on 5,277 digitized mammograms taken in 1995–2004 and was analyzed using multilevel models. Both ethnic minorities were characterized by more protective breast cancer risk factor distributions than Caucasians, such as later menarche, shorter stature, higher parity, earlier age at first birth, and less use of hormone therapy, but they had a higher mean body mass index; the last four factors were associated with lower mammographic density. Age-adjusted percent mammographic densities in Afro-Caribbeans and South Asians were 5.6% (95% confidence interval (CI): 3.5, 7.5) and 5.9% (95% CI: 3.6, 8.0) lower, respectively, than in Caucasians. Lower densities were partly attributed to higher body mass index, less use of hormone therapy, and a protective reproductive history, but these factors did not account entirely for ethnic differences, since fully adjusted mean densities were 1.3% (95% CI: –1.3, 3.7) and 3.8% (95% CI: 1.1, 6.3) lower, respectively. Ethnic differences in mammographic density are consistent with those for breast cancer risk.
breast neoplasms; ethnic groups; mammary glands, human; mammography
Abbreviations: BMI, body mass index; CI, confidence interval