Hidden Breast Cancer Disparities in Asian Women
Hidden Breast Cancer Disparities in Asian Women
Objectives. We estimated trends in breast cancer incidence rates for specific Asian populations in California to determine if disparities exist by immigrant status and age.
Methods. To calculate rates by ethnicity and immigrant status, we obtained data for 1998 through 2004 cancer diagnoses from the California Cancer Registry and imputed immigrant status from Social Security Numbers for the 26% of cases with missing birthplace information. Population estimates were obtained from the 1990 and 2000 US Censuses.
Results. Breast cancer rates were higher among US- than among foreign-born Chinese (incidence rate ratio [IRR]=1.84; 95% confidence interval [CI]=1.72, 1.96) and Filipina women (IRR=1.32; 95% CI=1.20, 1.44), but similar between US- and foreign-born Japanese women. US-born Chinese and Filipina women who were younger than 55 years had higher rates than did White women of the same age. Rates increased over time in most groups, as high as 4% per year among foreign-born Korean and US-born Filipina women. From 2000–2004, the rate among US-born Filipina women exceeded that of White women.
Conclusions. These findings challenge the notion that breast cancer rates are uniformly low across Asians and therefore suggest a need for increased awareness, targeted cancer control, and research to better understand underlying factors.
Breast cancer is the most common cancer diagnosed among US women. Nevertheless, in the United States, incidence rates vary substantially by standard racial/ethnic categories, with the lowest rates reported for Asians as a single group. However, within this group, breast cancer incidence rates vary further by specific ethnicity, with a nearly 3-fold difference between populations with the highest rate (Japanese women:126 per100000) and the lowest rate (Laotian women: 44 per100000). Moreover, within each of the Asian populations, there is substantial heterogeneity in lifestyles, health care practices, and risk factors that may correspond to important differences in breast cancer rates.
Higher breast cancer incidence rates among Asian women living in the United States than among those living in Asian countries, together with elevated breast cancer risks associated with immigration to and longer residence in the United States, have been centerpiece evidence for major roles for environmental, nongenetic factors in breast cancer causation. Earlier research has shown that immigrant status (US-born vs foreign-born) is associated with breast cancer risk through changes in reproductive factors (e.g., higher age at first live birth, lower breast feeding rates, earlier onset of menstruation) and lifestyle factors (e.g., diet) but could also indicate variations in other environmental exposures.
Examination of breast cancer incidence rates by immigrant status could inform these and other issues in breast cancer etiology. However, calculation of the accurate incidence rate trends by immigration status has been hampered by (1) nonrandom missing data on immigrant status for approximately 30% of cancer registry cases and (2) the lack of annual US Census estimates of Asian population counts according to immigrant status. To overcome these limitations, we augmented data on cancer cases from the population-based California Cancer Registry (CCR) through statistical imputation of immigrant status for cancer cases with missing birthplace and then used robust demographic methods to compute corresponding population estimates. With the resulting enhanced data resource, we sought to estimate breast cancer incidence rates by immigrant status, age, and time for specific Asian populations in California, the US state with the largest and most diverse Asian population.
Abstract and Introduction
Abstract
Objectives. We estimated trends in breast cancer incidence rates for specific Asian populations in California to determine if disparities exist by immigrant status and age.
Methods. To calculate rates by ethnicity and immigrant status, we obtained data for 1998 through 2004 cancer diagnoses from the California Cancer Registry and imputed immigrant status from Social Security Numbers for the 26% of cases with missing birthplace information. Population estimates were obtained from the 1990 and 2000 US Censuses.
Results. Breast cancer rates were higher among US- than among foreign-born Chinese (incidence rate ratio [IRR]=1.84; 95% confidence interval [CI]=1.72, 1.96) and Filipina women (IRR=1.32; 95% CI=1.20, 1.44), but similar between US- and foreign-born Japanese women. US-born Chinese and Filipina women who were younger than 55 years had higher rates than did White women of the same age. Rates increased over time in most groups, as high as 4% per year among foreign-born Korean and US-born Filipina women. From 2000–2004, the rate among US-born Filipina women exceeded that of White women.
Conclusions. These findings challenge the notion that breast cancer rates are uniformly low across Asians and therefore suggest a need for increased awareness, targeted cancer control, and research to better understand underlying factors.
Introduction
Breast cancer is the most common cancer diagnosed among US women. Nevertheless, in the United States, incidence rates vary substantially by standard racial/ethnic categories, with the lowest rates reported for Asians as a single group. However, within this group, breast cancer incidence rates vary further by specific ethnicity, with a nearly 3-fold difference between populations with the highest rate (Japanese women:126 per100000) and the lowest rate (Laotian women: 44 per100000). Moreover, within each of the Asian populations, there is substantial heterogeneity in lifestyles, health care practices, and risk factors that may correspond to important differences in breast cancer rates.
Higher breast cancer incidence rates among Asian women living in the United States than among those living in Asian countries, together with elevated breast cancer risks associated with immigration to and longer residence in the United States, have been centerpiece evidence for major roles for environmental, nongenetic factors in breast cancer causation. Earlier research has shown that immigrant status (US-born vs foreign-born) is associated with breast cancer risk through changes in reproductive factors (e.g., higher age at first live birth, lower breast feeding rates, earlier onset of menstruation) and lifestyle factors (e.g., diet) but could also indicate variations in other environmental exposures.
Examination of breast cancer incidence rates by immigrant status could inform these and other issues in breast cancer etiology. However, calculation of the accurate incidence rate trends by immigration status has been hampered by (1) nonrandom missing data on immigrant status for approximately 30% of cancer registry cases and (2) the lack of annual US Census estimates of Asian population counts according to immigrant status. To overcome these limitations, we augmented data on cancer cases from the population-based California Cancer Registry (CCR) through statistical imputation of immigrant status for cancer cases with missing birthplace and then used robust demographic methods to compute corresponding population estimates. With the resulting enhanced data resource, we sought to estimate breast cancer incidence rates by immigrant status, age, and time for specific Asian populations in California, the US state with the largest and most diverse Asian population.
