Age-period-cohort projections of breast cancer incidence in a rapidly transitioning Chinese population.

Breast cancer incidence should be assessed separately in different populations, as it differs substantially between Chinese and Caucasian women, and more generally in developing versus developed populations. Estimation of future trends is important for public health planning. On the basis of the recent breast cancer incidence trends, we projected future disease rates in the rapidly transitioning Chinese population of Hong Kong. We used local data on breast cancer incidence and mid-year population figures for the years 1974-2003. We fitted Poisson age-period-cohort models with autoregressive priors on the age, period and cohort effects, and used projections of these effects to forecast future incidence to 2018. We found that age-standardized breast cancer incidence would continue to rise by approximately 1.1% per annum over the next 15 years, from 45.9 cases in 1999-2003 to 54.3 per 100,000 (95% credible interval: 50.9, 58.4) in 2014-2018. Recent secular incidence increases can be attributed to both ageing and intergenerational effects beginning with the postwar baby boomers, whereas there is no evidence for important changes by time period. There does not appear to be differential cohort-related risk for pre- vs. postmenopausal disease. Unlike most other cancers, breast cancer risk in local women would continue to increase in the short to medium term, at a similar rate of increase compared with historical trends. This could most likely be attributed to Hong Kong's socioeconomic developmental history and continuing adoption of westernized lifestyle changes.