Article

Age-Related Crossover in Breast Cancer Incidence Rates Between Black and White Ethnic Groups

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 20892-7244, USA.
Journal of the National Cancer Institute (Impact Factor: 12.58). 01/2009; 100(24):1804-14. DOI: 10.1093/jnci/djn411
Source: PubMed

ABSTRACT

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.
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.
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).
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.

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    • "Breast cancer is the most common cancer among women in the United States, accounting for 29% of all newly diagnosed cancers [1]. Although breast cancer incidence at older ages is lower among African American (AA) women than European American (EA) women, the incidence rate is higher in AA women at younger ages (50 years) [2]. More importantly, AA women are more likely to be diagnosed with aggressive tumors that are high grade and negative for estrogen receptors (ER), which are often associated with poorer disease prognosis [3]. "
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    • "Some authors argue that the crossover is not a true feature of breast cancer rate curves, instead suggesting that the crossover would disappear after adjusting the rates to account for birth cohort or time period effects [31,32] . However, age-period-cohort (APC) analysis on agespecific breast cancer incidence rate curves performed in [30] proved that this crossover remains after accounting for birth cohort and time period effects. In other work [28], it was proposed that the race-specific differences can be explained by differences in well-known risk factors (such as older age at first birth, fewer births, younger age of menarche). "
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