Abstract LB-288: Differential cohort effect on early- and late-onset breast cancer incidence among Chinese women in different populations
Authors: Sung Hyuna , Rosenberg Philip S. , Chen Wan-Qing , Hartman Mikael , Lim Wei-yen , Chia Kee Seng , Mang Oscar Wai-kong , Tse Shelly Lap-ah , Anderson William F. , Yang Xiaohong R. 
Published: May 2015

Abstract
Introduction: Breast cancer incidence rates are much lower in Asian women than in Western women. However, the incidence rates in Asian countries are rapidly increasing in the recent decades and this dramatic rise has been largely attributed to a strong birth-cohort effect. For example, some of the well-established breast cancer risk factors may interact with age which may in turn lead to differential cohort effect among early- and late-onset breast cancers.
Methods: We analyzed the incidence and population data (1988 through 2009) among Chinese women obtained from population-based cancer registries in different countries or geographical areas (urban China, rural China, Singapore, and the United States). The cohort relative risks adjusted for age and period effects were estimated separately for women younger than 50 years (30-49) and women age 50 or older (50-79) using the respective mid-year birth cohort as referent (1934 for older and 1960 for younger women, respectively).
Results: Breast cancer incidence has increased in all Chinese populations examined, particularly in women aged 50-79 years with estimated annual percentage change (EAPC) ranging from 2.00%/year (95% CI, 0.95-3.07) for Chinese American to 6.24%/year (95% CI, 4.95-7.55) for rural China. In contrast, rates for younger women aged 30-49 were stable or increased at a slower rate with EAPC from -0.33%/year (95% CI, -1.39-1.08) for Chinese American to 4.72%/year (95% CI, 3.92-5.52) for rural China. The cohort relative risks of breast cancer in older women rose significantly in successive birth cohorts in all Chinese populations with the most dramatic 4.0-fold (95% CI, 3.07-5.24) increase seen in rural China and a more modest 1.7-fold (95% CI, 1.24-2.23) increase among Chinese American women born from 1934 to 1958. In contrast, the increases in cohort relative risk among younger women were markedly lower or non-significant in all Chinese populations except for rural Chinese women (2.1-fold; 95% CI, 1.36-3.17) born from 1960 to 1978. Consistently, the projection of future incidence also showed a greater increase in late-onset breast cancer than in early-onset breast cancer.
Conclusions: Our findings suggest that cohort effect-driven risk of breast cancer attributed to rapid socioeconomic development and concurrent westernization in Asian countries has and will continue to result in an upsurge in breast cancer incidence, especially in older women. Our data further supports the previous hypothesis that early- and late-onset breast cancers might derive from distinct etiologic pathways.
Citation Format: Hyuna Sung, Philip S. Rosenberg, Wan-Qing Chen, Mikael Hartman, Wei-yen Lim, Kee Seng Chia, Oscar Wai-kong Mang, Shelly Lap-ah Tse, William F. Anderson, Xiaohong R. Yang. Differential cohort effect on early- and late-onset breast cancer incidence among Chinese women in different populations. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-288. doi:10.1158/1538-7445.AM2014-LB-288