Journal of the National Cancer Institute Advance Access published online on December 9, 2008
JNCI Journal of the National Cancer Institute, doi:10.1093/jnci/djn411
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Published by Oxford University Press 2008.
ARTICLES |
Age-Related Crossover in Breast Cancer Incidence Rates Between Black and White Ethnic Groups
Affiliations of authors: Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, United States Department of Health and Human Services, Bethesda, MD (WFA, PSR, IM, RMP); Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT (AM)
Correspondence to: William F. Anderson, MD, MPH, Biostatistics Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, United States Department of Health and Human Services, EPS, Rm 8036, 6120 Executive Blvd, Bethesda, MD 20892-7244 (e-mail: wanderso{at}mail.nih.gov).
Background: Although breast cancer incidence is higher in black women than in white women among women younger than 40 years, the reverse is true among those aged 40 years or older. This crossover in incidence rates between black and white ethnic groups has been well described, has not been completely understood, and has been viewed as an artifact.
Methods: To quantify this incidence rate crossover, we examined data for 440 653 women with invasive breast cancer from the National Cancer Institute’s Surveillance, Epidemiology, and End Results database from January 1, 1975, through December 31, 2004. Data on invasive female breast cancers were stratified by race, age at diagnosis, year of diagnosis, and tumor characteristics. Standard descriptive analyses were supplemented with Poisson regression models, age–period–cohort models, and two-component mixture models. All statistical tests were two-sided.
Results: We observed qualitative (ie, crossing or reversing) interactions between age and race. That is, age-specific incidence rates overall (expressed as number of breast cancers per 100 000 woman-years) were higher among black women (15.5) than among white women (13.1) younger than 40 years (difference = 2.4, 95% confidence interval [CI] = 2.4 to 2.4), and then, age-specific rates crossed with rates higher among white women (281.3) than among black women (239.5) aged 40 years or older (difference = 41.8, 95% CI = 41.7 to 41.9). The black-to-white incidence rate crossover was observed for all tumor characteristics assessed, although the crossover occurred at earlier ages of diagnosis for low-risk tumor characteristics than for high-risk tumor characteristics. The incidence rate crossover between ethnic groups was robust (ie, reliable and reproducible) to adjustment for calendar period and birth cohort effects in age–period–cohort models (P < .001 for difference by race).
Conclusion: Although this ecologic study cannot determine the individual-level factors responsible for the racial crossover in vital rates, it confirms that the age-related crossover in breast cancer incidence rates between black and white ethnic groups is a robust age-specific effect that is independent of period and cohort effects.
| CONTEXT AND CAVEATS Prior knowledge The incidence rate for breast cancer among women younger than 40 years is higher among black women than among white women, but the incidence rate among women aged 40 years or older is higher among white women than among black women. Study design Population-based retrospective analysis of data for 440 653 women with invasive breast cancer from the National Cancer Institute's Surveillance, Epidemiology, and End Results database from January 1, 1975, through December 31, 2004. Contribution The age-specific ethnic crossover in incidence rates for breast cancer was confirmed. Implications The breast cancer incidence rate crossover between black and white ethnic groups may reflect breast cancer heterogeneity, with black women having more early-onset and less late-onset types of breast cancer than white women. Limitations This study had the usual limitations of a descriptive epidemiologic study, including a retrospective registry assessment, missing data, nonstandardized histopathologic typing, and lack of individual-level risk factor data. From the Editors
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Manuscript received June 24, 2008; revised September 18, 2008; accepted October 10, 2008.
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J Natl Cancer Inst 2008 100: 1741.
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