The first report, Cancer Trends: Trends in cancer incidence by ethnic and socioeconomic group, New Zealand 1981-2004, plots trends over time in the incidence rates of cancers by ethnicity and household income using linked census-cancer registry data. It was funded by the Health Research Council of New Zealand.
“There are many surprising findings. For example, endometrial and thyroid cancer rates were consistently three times higher among Pacific women than European women,” says study leader Professor Tony Blakely.
“Obesity may be a partial reason why endometrial cancer rates are higher among Pacific women, but it is far from a complete explanation.”
Conversely, there are cancers where the rates are highest among Europeans, melanoma being the most obvious example. Other examples included brain, colorectal (although Māori rates are approaching European rates over time) and bladder cancers. Pacific and Asian kidney cancer rates were half those of Māori and European/Other. These differences are not understood, and require further research.
Trends in cervical cancer incidence demonstrate a public health success story. Rates have halved in 25 years, and fell most dramatically among Māori and Pacific women. This is presumably due to cervical cancer screening. Nevertheless, rates in 2001-04 were still twice as high among Māori and Pacific women compared to European women, pointing to the need to further increase Māori and Pacific participation in screening.
Lung cancer – the cancer most strongly associated with smoking – has increased since 1981 for both Māori and European females, but decreased for both Māori and European males. At any one point in time, though, Māori rates were two to three times European rates, and rates among low income groups up to twice high income groups.
Breast cancer rates have increased in all ethnic groups, but most rapidly amongst Māori females, such that Māori rates were a third higher than European rates in 2001-04. High income women consistently had 10% to 20% higher rates than low income women. The faster rate of increase in breast cancer among Māori females is probably attributable to rapid falls in fertility among Māori, but it is surprising that Maori rates are higher at any one point in time.
The second report, The Burden of Cancer, combines the above incidence rates with cancer survival and mortality data, and determines a composite measure of ‘burden’. This burden measures years of life lost due to early death from cancer, and years of life lived in less than full health.
Māori cancer burden per head of population was greater than non-Māori cancer. This is due to the combined effect of often having higher incidence rates, and just about always having worse survival once diagnosed. For example, the Māori burden was over three times the non-Māori burden for lung, liver and testicular cancer, and two to three times greater for cervical, laryngeal, stomach and endometrial cancers.
Professor Blakely says the health services have a role in reducing these ethnic inequalities, both through prevention programmes and quality health care services.
Among males, lung, prostate and colorectal cancers were the three top ranked cancers in burden for both Māori and non-Māori. Prostate cancer was the highest rank among non-Māori (17.0% of all non-Māori male cancer burden) whereas among Māori males lung cancer was the highest ranked (24.1%).
Among females, breast, lung and colorectal were the three highest ranked cancers in terms of burden, and in this rank order for both Māori and non-Māori. However, among Māori lung cancer was nearly as great as the breast cancer burden.
Professor Blakely says that the methods and results in these reports are now contributing to a new research programme funded by the Health Research Council of New Zealand, the Burden of Disease Epidemiology, Equity and Cost-Effectiveness Programme. This programme will estimate the relative impact, and cost effectiveness, of interventions to reduce the burden of cancer in New Zealand.
For further information contact
Professor Tony Blakely
Director, Burden of Disease Epidemiology, Equity and Cost-Effectiveness Programme
Department of Public Health
University of Otago,Wellington