Lifetime risk of most common cancers overstated: new research

Doug Hendrie

11/11/2019 12:08:27 PM

Australia’s five most common cancers are less of a lifetime risk than previously thought – particularly for men.

cancer cells dividing
Cancer is common – but not quite as common as people think, according to this study.

The findings in a new MJA study take into account competing mortality when calculating the lifetime risk of the five most common cancers in Australia – breast cancer, colorectal cancer, prostate cancer, melanoma of the skin, and lung cancer.
The study found all five cancers have lower lifetime risks under the competing mortality model, compared to the co-morbidity model used by the Australian Institute of Health and Welfare (AIHW), between 1982 and 2013.
Prostate cancer risk differed by the most between the two models, with the AIHW’s data giving an 18.7% risk of 2013, compared to 16.2% with the competing mortality model.
Colorectal cancer risk for men also differed significantly, falling from 9% (AIHW) to 7% (new model).
That’s the equivalent of shifting from a one in 11 lifetime risk of colorectal cancer to a one in 14 risk.
The competing mortality approach takes into account the fact that the population at risk of cancer declines as people die of other causes, whereas the co-morbidity approach assumes no competing causes of death.  
Research co-author Dr Anthea Bach told newsGP she believed the research was important.
‘The risks were lower than previously published in all five cancers. With prostate cancer, it’s quite a big difference,’ she said.
‘This has impacts on the general public as well as the medical field. The perception of cancer risk is always in the back of people’s minds. We want perceptions of risk to be as accurate as possible.’
Dr Bach stressed the new research was not a criticism of the AIHW and its statistical methods.
‘We are slowly seeing a shift internationally to accounting for competing mortality,’ she said. 
‘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.’
GP researcher and Bond University Professor of Evidence-Based Medicine Paul Glasziou told newsGP the study he co-authored would lead to changes in public messaging.
‘It’s not that the figures have been hugely inaccurate, but people quote them – so we think they need to be corrected to appropriately take into account the competing risks,’ he said.
‘Across the board, most statements about the lifetime risk of cancer have been overestimated because competing risks aren’t taken into account. If you die of a heart attack at 65, you can’t die of cancer at 75 – but the current research acts as if you could.’
Professor Glasziou said the difference between the two methods is reducing over time, due to better healthcare and reduced risks of other major causes of death, such as cardiovascular disease.
In an accompanying statement, the authors suggest 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 the Sydney Morning Herald his organisation is aware of the different methodology, but stressed the one they currently use is the worldwide standard.
‘The competing mortality method has advantages in more accurately estimating lifetime risks of diagnosis and death from cancer. 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,’ he said.
Mr Juckes said the AIHW is considering using the competing mortality method used in the new research, but stressed that the current single-mortality method is the best for comparing between populations.
In 2013, the estimated lifetime risks of diagnosis (AIHW and competing mortality adjusted) were: 

  • 12.7% and 12.1% for breast cancer
  • 18.7% and 16.2% for prostate cancer
  • 9.0% and 7.0% (men) and 6.4% and 5.5% (women) for colorectal cancer
  • 7.5% and 6.0% (men) and 4.4% and 4.0% (women) for melanoma of the skin
  • 7.6% and 5.8% (men) and 4.5% and 3.9% (women) for lung cancer

AIHW breast cancer cancer data lifetime risk lung cancer prostate cancer

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Dr Craig Martin Lilienthal   12/11/2019 8:17:59 AM

Great. My risk of dying of prostate cancer has gone down from 18.7% to 16.2% because I could die of breast cancer, colorectal cancer, melanoma or lung cancer.
However, as I am male, have regular FOBTs and the occasional colonoscopy, did not spend my youth in the sun and stopped smoking 50 years ago, (and have no evidence of coronary artery disease) does this mean my risk of prostate cancer has in fact increased - despite there being no FH of prostate cancer?

Dr Horst Paul Herb   12/11/2019 5:30:51 PM

Well Craig, if you ejaculate regularly, your prostate cancer risk goes down, and if you don't have a father or brother with prostate cancer, you risk plummets further ...

The point of such risk estimates are valid for the population as a whole, not for an individual. They give you good information as to how worthwhile it could be to modify modifiable risk factors if your aim is to do better (or worse?) than the average in that population.

They also might guide funding for research, primary prevention, screening, etc - hence we need the most realistic estimate possible, and that includes accounting for competing causes of death.