Abstract B53: Breast cancer incidence in U.S. Asian women by nativity

Background: Female breast cancer incidence rates have long been recognized to be lower among Asians than other racial/ethnic groups in the U.S. However, there is great heterogeneity in the U.S. Asian population, not only by specific ethnicity, but also by nativity (U.S.- versus foreign-born). Unfortunately, incidence data are currently inadequate for monitoring breast cancer trends in detailed Asian populations, and to meaningfully inform public health and clinical recommendations.

Objective: Using rigorously derived nativity case data and population estimates, we investigated patterns in breast cancer incidence for Chinese, Japanese, Filipino, Korean, South Asian, and Vietnamese women in California by nativity, age, and over time between 1988 and 2004.

Methods: For the 27.2% of cases missing birthplace information in the cancer registry, nativity was imputed from Social Security number sequences. We also used robust demographic methods to compute corresponding population estimates, based on published Census 1990 and 2000 data. Ethnic- and nativity-specific age-adjusted incidence rates were calculated, with annual percentage changes derived from Joinpoint regression analysis.

Results: U.S.-born women had higher incidence rates than foreign-born, with incidence rate ratios (IRR) comparing the US-born to their respective foreign-born counterparts higher for Chinese (IRR=1.84, 95% CI: 1.72–1.96) and Filipinas (IRR=1.32, 95% CI: 1.20–1.44) than for Japanese in whom rates were equivalent (IRR=1.03; 95% CI: 0.96–1.10). Among younger women (<55 years), rates among US-born Chinese and Filipinas were higher than those for non-Hispanic white women, while rates among U.S.-born Asian women age 55 and older were considerably lower. Rates were also shown to increase over time for most populations, with foreign-born Koreans and U.S.- born Filipinas having the largest annual increases (annual percentage change = 4.2%). In the latest time period (2002–2004), rates were highest among U.S.-born Filipinas, at 171.4 per 100,000.

Conclusion: We observed that U.S.-born Asian ethnic populations had up to two-fold higher rates than their foreign-born counterparts, except for Japanese women. The higher rates of breast cancer in U.S.-born Chinese and Filipinas, and the lack of differences between U.S.- and foreign-born Japanese, are suggestive of a considerably larger role for environmental than genetic factors in the etiology of this disease. Furthermore, while some of these patterns are consistent with changes in risk factors that are related to acculturation, the age- and time-dependent patterns may offer unique clues into as yet unidentified risk factors. These findings contradict the longstanding notion that breast cancer rates are uniformly low among Asians in this country and highlight the need for targeted cancer control efforts for these groups. As the number of U.S.-born Asians continues to rise, breast cancer will become an increasingly prominent public health problem in this population.