Racial and ethnic disparities in breast cancer rates by age: NAACCR Breast Cancer Project.

OBJECTIVE: To examine age-specific rates of breast cancer incidence among racial and ethnic groups in the United States.
METHODS: Subjects were 363,801 women diagnosed with invasive breast cancer diagnosed during 1994--1998 and reported in the North American Association of Central Cancer Registries (NAACCR) data set. Variables analyzed included race, ethnicity, 5-year age group (from 10 years through 85+years), and stage at time of diagnosis (localized, regional, distant). Incidence rates per 100,000 women were calculated for each 5--year age group and stratified by stage. Rate ratios and 95% confidence intervals were calculated by comparing each racial group with whites and Hispanics with non-Hispanics.
RESULTS: Black women experience significantly higher breast cancer incidence up to the age of 40 years and significantly lower incidence after age 50 compared with white women of the same ages. This is called the 'crossover' effect. This shifting burden of higher incidence occurs at ages 35--39 for localized stage and at ages 55--59 for regional stage. For distant stage, black women of all ages experience higher incidence compared with white women. Similar crossover effects do not exist for American Indian (AI) or Asian/Pacific Islander (API) women compared with white women. Both AI and API women have significantly lower incidence of breast cancer compared with white women, and Hispanic women have significantly lower incidence compared with non-Hispanic women.
CONCLUSIONS: This study highlights racial and ethnic differences in breast cancer incidence rates among US women. The crossover effect between black and white women, particularly the lower incidence of localized stage disease diagnosed in older black women, is a significant phenomenon that may be associated with screening practices, and has implications for public health planning and cancer control initiatives to reduce racial/ethnic disparities.