Background Age-specific cancer incidence patterns provide insight into carcinogenic mechanisms, timing of risk exposures, screening effects, and generational shifts in cancer burden, making them a valuable tool for comparing cancer risks across populations. However, most studies employed cross-sectional assessment at single calendar years or aggregated time intervals, which may mask underlying period effects and longitudinal changes in risk exposures over the life course (e.g., birth cohort effect). Longitudinal analyses are essential for properly capturing age-specific incidence patterns.
Objective To compare age-specific incidence rates between women in Asian countries and ethnicity-corresponding Asian American women using both cross-sectional and longitudinal approaches
Methods Breast cancer incidence and population denominator data for women aged 30-79 from 2000-2019 were obtained from 21 Surveillance, Epidemiology, and End Results registries in the United States; Cancer Incidence in Five Continents Plus for mainland China, Philippines, India, and Japan (2000-2015); and national cancer registries for Taiwan, Japan (2016-2019), and South Korea. Age-specific incidence rates per 100,000 person-years were estimated using (1) cross-sectional approaches based on aggregated diagnosis years and (2) longitudinal approaches. Longitudinal estimates were derived from age–period rate matrices constructed using 2-year age groups and 2-year calendar periods, yielding overlapping birth cohorts spanning 1921-1923 to 1987-1989, with adjustment for period and cohort deviations.
Results Based on cross-sectional age curves, age-specific incidence rates were substantially higher among Asian American women compared with women in their countries of origin, with particularly large differences at ages older than 50 (rate ratios at age 70, 1.52–2.58). In contrast, longitudinal age-specific curves for women in Japan, Korea, and Taiwan largely overlapped across all age bands and, at older ages, in some cases exceeded those of ethnicity-corresponding Asian Americans. However, substantial differences persisted in longitudinal age curves for women of Indian, Filipino, and Chinese descent, with Asian American women continuing to exhibit considerably higher incidence rates than women in their countries of origin.
Conclusions The near disappearance of longitudinal age incidence rate differences for women in Japan, Korea, and Taiwan suggests that women in these Asian countries/territories now experience breast cancer incidence comparable to that of their counterparts residing in the United States. In contrast, the persistent gaps observed among women of Indian, Filipino, and Chinese descent indicate incomplete convergence, suggesting heterogeneity in cohort effects, risk factor adoption, or diagnosis practices across Asian populations that warrant further investigation.