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Open Access Research article

Ethnic differences in the time trend of female breast cancer incidence: Singapore, 1968 – 2002

Xueling Sim1, R Ayesha Ali2, Sara Wedren3, Denise Li-Meng Goh145, Chuen-Seng Tan1, Marie Reilly3, Per Hall3 and Kee-Seng Chia136*

Author Affiliations

1 Centre for Molecular Epidemiology, National University of Singapore and Genome Institute of Singapore, Singapore

2 Department of Mathematics and Statistics, University of Guelph, Canada

3 Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Sweden

4 Department of Paediatrics, National University of Singapore, Singapore

5 Centre for Molecular Medicine, Biomedical Research Council, Agency for Science, Technology and Research, Singapore

6 Department of Community, Occupational and Family Medicine, National University of Singapore, Singapore

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BMC Cancer 2006, 6:261  doi:10.1186/1471-2407-6-261

Published: 2 November 2006

Abstract

Background

From 1968 to 2002, Singapore experienced an almost three-fold increase in breast cancer incidence. This increase appeared to be different across the three main ethnic groups: Chinese, Malays and Indians. This paper used age-period-cohort (APC) modelling, to determine the effects of age at diagnosis, calendar period, and birth cohort on breast cancer incidence for each ethnic group.

Methods

This study included all breast cancer cases (n = 15,269) in the three ethnic groups, reported to the Singapore Cancer Registry from 1968 to 2002 between the ages 25 to 79. Age-specific fertility rates from the Department of Statistics were used to explore the role of fertility.

Results

In the 1970s, Indian women had the highest age-standardized breast cancer but by the mid-1980s the highest rates were seen among the Chinese. Remarkable differences were seen in the age-specific incidence rates by ethnic groups. After age 49, the incidence rates for the Chinese and Malays leveled off whereas it continued to rise in the Indians. While our analyses provided some evidence that an age-drift model described the trend seen in the Indians, age-period-cohort model and age-cohort model had the best fit for the Chinese and Malays aged 25 to 79 respectively. Overall, Chinese and Malay women born in later cohorts were at increased risk of developing breast cancer relative to their counterparts in the earlier cohorts. The three ethnic groups experienced similar changes in their fertility in the 1970s, which likely explained much of the increase in their breast cancer incidence but not the ethnic differences. There was a stronger inverse association between total fertility rate and pre-menopausal breast cancer incidence in the Chinese and Malays than the Indians.

Conclusion

The observed dissimilarity among ethnic groups suggests ethnic differences in exposure or response to certain risk factors. It is likely that longer and subtler differences in childbearing trends and other risk factors may further explain these ethnic differences.