Modelling predictions of cancer deaths in Northern Ireland

An ageing population has service planners concerned about future levels of disease which are age dependent. Predictions of mortality for colorectal, lung and breast cancers, which account for 30% of cancer cases and 40% of cancers deaths, were calculated for 2010 and 2015, based on trends in death rates and the predicted change in the demography of the Northern Ireland population.

The U.S. National Cancer Institute's "Joinpoint" program was used to check for structural breaks in the time series of cancer death rates from 1984 to 2004. The prediction models applied to the data allowed variations in trends across age groups to be taken into account. A linear model was used for increasing or constant trends and a log linear model was used where the trend was decreasing. The models assume the number of deaths in each stratum, defined by age-sex and time-period, is Poisson distributed, with the average value determined by a log or linear function.

Recent trends in rates of cancers studied were downwards except for female lung. Predictions include decreased colorectal cancer deaths in females and lung cancer deaths in males. In females, lung cancer deaths are predicted to more than double by the year 2015 (473 deaths), based on the 1984 level. Colorectal death rates in males are predicted to drop, but the number of deaths will increase by more than 10%, due to demographic change. Numbers of breast cancer deaths are likely to rise slightly, despite falling age standardised death rates, due to an ageing population.

This work has provided estimates of early future trends, useful to service planners, and highlights the need for tobacco control, to reduce numbers of lung cancer deaths in females. The recently announced control of environmental tobacco legislation is one welcome development which should reduce lung cancer mortality in Northern Ireland.