The bad news may not be that bad. The method used in Australia to calculate a person’s lifetime risk of cancer has been overestimated, especially for men, according to a paper published this week in the Medical Journal of Australia.
The authors say that the method used by the Australian Institute of Health and Welfare (AIHW) to calculate risk assumes that there are no competing causes of death. This means that the risk of dying from cancer, as calculated by the AIHW and then used by government agencies and other organisations in campaigns, is likely to be overstated.
This was particularly so when estimating the likelihood of developing prostate cancer.
“Prostate cancer was the biggest overestimation,” said Dr Anthea Bach, from West Moreton Hospital and Health Service. “Going back to 1993, the AIHW published the risk of 22.5 per cent of getting prostate cancer. We calculated it was 14.4 per cent.
“That’s the difference between a one-in-four chance of getting prostate cancer and a one-in-seven chance.”
Dr Bach and Dr Kelvin Lo, from Westmead Hospital, analysed publicly available annual AIHW data on age-specific cancer incidence and mortality – for breast cancer, colorectal cancer, prostate cancer, melanoma and lung cancer – between 1982 and 2013. They calculated lifetime risks of cancer diagnosis and cancer-specific death, adjusted for competing mortality, and compared their estimates with the corresponding risks published by the AIHW.
“AIHW estimates were consistently higher than our competing mortality-adjusted estimates of lifetime risks of diagnosis and death for all five cancers,” they said.
“Differences between AIHW and adjusted estimates declined with time for breast cancer, prostate cancer, colorectal cancer and lung cancer (for men only), but remained steady for lung cancer (women only) and melanoma.”
In 2013, the respective estimated lifetime risks of diagnosis (AIHW) and adjusted rates were:
- breast cancer – 12.7 per cent and 12.1 per cent
- prostate cancer – 18.7 per cent and 16.2 per cent
- colorectal cancer – 9 per cent and 7 per cent (men) and 6.4 per cent and 5.5 per cent (women)
- melanoma – 7.5 per cent and 6 per cent (men) and 4.4 per cent and 4 per cent (women)
- lung cancer – 7.6 per cent and 5.8 per cent (men) and 4.5 per cent and 3.9 per cent (women).
The authors stressed that they were not criticising the AIHW.
“The method used by the AIHW is employed by many cancer registries; further, software that facilitates accounting for competing risk was not available when AIHW began calculating lifetime risks,” they said.
The implications of the study results were that, “as lifetime risk estimates are widely cited in health promotion campaigns, they may cause public misperceptions of the risk of a cancer diagnosis or death”, the authors added.
“Australian agencies should consider adopting methods for adjusting for competing mortality when estimating lifetime risks, as currently employed in North America and the United Kingdom, to increase the accuracy of their estimates.”
AIHW head of Health Group Richard Juckes told Nine media they were aware of the different methodology, but stressed that the one they currently used was the worldwide standard.
“The competing mortality method has advantages in more accurately estimating lifetime risks of diagnosis and death from cancer,” he said.
“However, for the purpose of international comparisons, it is better to have Australian estimates calculated on the same basis as other countries than to use estimates that aren’t as comparable.”
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