1. ¹Department of Community Medicine, University of Hong Kong, 5/F, Academic & Administration Block, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong, China
2. ²Hong Kong Cancer Registry, Hospital Authority, c/o Department of Clinical Oncology, Queen Elizabeth Hospital, 30 Gascoigne Road, Kowloon, Hong Kong, China
3. ³Department of Statistics and Actuarial Science, University of Hong Kong, Pokfulam Road, Hong Kong, China
4. ⁴Department of Community and Family Medicine, Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China
5. ⁵Cancer Expert Working Groups (Prevention and Screening; Data and Priorities), Cancer Coordinating Committee, Health, Welfare and Food Bureau, Government of the Hong Kong Special Administrative Region, Murray Building, 3 Garden Road, Central, Hong Kong, China

Correspondence: Dr G M Leung, E-mail: gmleung@hku.hk

Received 12 June 2002; Revised 6 August 2002; Accepted 12 August 2002.

Abstract

Hong Kong has the highest breast cancer incidence in Asia and studying secular changes in its rates may lead to hypotheses regarding disease aetiology and also predictions of future trends for China. We examined statistics from the Hong Kong Cancer Registry based on 26 566 cases of invasive breast cancer from 1973 to 1999. The trends in breast cancer incidence were studied using log-linear longitudinal models. We further analysed the independent effects of chronological age, time period and birth cohort on incidence trends using age-period-cohort modelling. The average annual per cent change of the age-standardised incidence was 3.6% during 1973–1999. Age-period-cohort modelling indicated the incidence development was predominantly a cohort effect, where the rise in relative risk was seemingly linear in successive birth cohorts, showing a 2–3-fold difference when comparing women born in the 1960's with those born around 1900. Our results suggest that direct and indirect consequences of westernisation may have been responsible for most of the observed increase in breast cancer incidence. As China moves towards a more westernised way of life, we can expect an emerging epidemic of breast cancer as Hong Kong's experience has demonstrated.