Are we overestimating lifetime cancer risks?

11 November 2019
Researchers have found current estimates of lifetime risks of cancer diagnosis and mortality consistently higher than when they allowed for competing causes of death.

The method used in Australia to determine estimates of lifetime risks of cancer diagnosis and mortality could lead to an overestimation of these risks, especially for men, according to University of Sydney and Bond University researchers.  

Cancer registries and organisations such as the Australian Institute of Health and Welfare (AIHW) use age specific cancer incidence and mortality data in a calendar year to estimate lifetime risks of cancer diagnosis and mortality.

However, the method used to achieve these numbers assumes there are no competing causes of death, which may lead to overestimation of lifetime risk and the researchers have recommended that the more accurate methodology be adopted.

The findings were published online today in the Medical Journal of Australia.

Dr Katy Bell from the University of Sydney's Faculty of Medicine and Health, was senior author on the analysis, which was led by Dr Anthea Bach from West Moreton Hospital and Health Service and Dr Kelvin Lo from Westmead Hospital. Sydney's Professor Alexandra Barratt, also from the School of Public Health, was also involved in the study.

The researchers calculated their own estimates on lifetime risks of cancer diagnosis and cancer-specific death, adjusted for competing mortality, and compared their findings 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,” Dr Bell and colleagues wrote.  

The authors analysed publicly available annual AIHW data on age-specific cancer incidence and mortality — for breast cancer, colorectal cancer, prostate cancer, melanoma of the skin, and lung cancer — and all-cause mortality in Australia, between 1982 and 2013.

Key findings

  • Differences between AIHW and adjusted estimates declined with time for breast cancer, prostate cancer, colorectal cancer, and lung cancer (for men only).
  • However this remained steady for lung cancer (women only) and melanoma of the skin.
  • In 2013, the respective estimated lifetime risks of diagnosis (AIHW and adjusted) were 12.7 percent and 12.1 percent for breast cancer, 18.7 percent and 16.2 percent for prostate cancer, 9.0 percent and 7.0 percent (men) and 6.4 percent and 5.5 percent (women) for colorectal cancer, 7.5 percent and 6.0 percent (men) and 4.4 percent and 4 percent (women) for melanoma of the skin, and 7.6 percent and 5.8 percent (men) and 4.5 percent and 3.9 percent (women) for lung cancer.

Not a criticism

The authors stressed that they were not criticising the AIHW, stating that when organisations such as AIHW began calculating lifetime risks, the methods and software required to account for competing did not exist.

“Our results indicate that cancer agencies, including the AIHW, may overestimate the risks of people being diagnosed with or dying from a particular cancer,” Dr Bell and colleagues wrote.  

However, Dr Bell and colleagues say lifetime risk estimates are widely cited in health promotion campaigns – and in health promotion campaigns, which may cause public misperceptions of the risk of a cancer diagnosis or death.

“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,” the authors concluded.

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