Many cancers are caused by exposure to lifestyle, environmental, and occupational factors. Earlier studies have estimated the number of cancers occurring in a single year which are attributable to past exposures to these factors. However, there is now increasing appreciation that estimates of the future burden of cancer may be more useful for policy and prevention. We aimed to calculate the future number of cancers expected to arise as a result of exposure to 23 modifiable risk factors.
We used the future excess fraction (FEF) method to estimate the lifetime burden of cancer (2016–2098) among Australian adults who were exposed to modifiable lifestyle, environmental, and occupational risk factors in 2016. Calculations were conducted for 26 cancer sites and 78 cancer-risk factor pairings.
The cohort of 18.8 million adult Australians in 2016 will develop an estimated 7.6 million cancers during their lifetime, of which 1.8 million (24%) will be attributable to exposure to modifiable risk factors. Cancer sites with the highest number of future attributable cancers were colon and rectum (n = 717,700), lung (n = 380,400), and liver (n = 103,200). The highest number of future cancers will be attributable to exposure to tobacco smoke (n = 583,500), followed by overweight/obesity (n = 333,100) and alcohol consumption (n = 249,700).
A significant proportion of future cancers will result from recent levels of exposure to modifiable risk factors. Our results provide direct, pertinent information to help determine where preventive measures could best be targeted.
- ● Around 1.8 million future cancers will be due to exposure to lifestyle factors.
- ● This represents 24% of future cancers in this cohort of adult Australians.
- ● Cancers of the colon and rectum will comprise the highest number of future cancers.
- ● Tobacco smoke will contribute the largest number of future cancers.
Cancer is a leading public health concern with a significant social and economic impact. It accounted for approximately 18% of the total disease burden in Australia in 2019 , with 145,000 cases estimated to have been diagnosed in 2020 . A high proportion of these cancers are caused by exposure to lifestyle, and occupational factors . Many of these factors are modifiable, meaning that the future number of cancers in our society could be reduced by minimising or, where possible, eliminating these exposures.
Historically, the most common approach to estimating the number of cancers caused by various risk factors has been the population attributable fraction (PAF) approach. This method is generally used to estimate the proportion of cancer cases occurring in a single year which is attributable to past exposures . In Australia, previous studies have estimated that 32–44% of the cancer burden in a single year was attributable to lifestyle exposures . This is comparable to estimates from other countries, including the United Kingdom (UK; 38% of cases in 2015) , United States (US; 42% of cases in 2014) , and Canada (41% of cases in 2012) .
There is now increasing appreciation that estimates of the future burden of cancer – that is, the number of cancer cases which might occur in the future as a result of current exposures – may be more useful for policy and prevention than estimates based on past cancer incidence and exposure . A growing body of work has estimated the future burden of cancer using various methods, including work in Canada and the UK . In Australia, variations on the PAF method have been used to predict future cancers attributable to lifestyle exposures. For example, Laaksonen and colleagues used pooled cohort data to estimate the PAF of various cancers due to modifiable factors over 10 years (from 2017 to 2026) . They found that smoking, overweight and obesity, and alcohol consumption contributed the highest number of cancers during that period . In an alternative approach, Wilson and colleagues used a dynamic simulation model incorporating latency estimates to predict future cancers attributable to lifestyle factors over a 25 year period (2013–2037) . They estimated that 7–13% of weight-related cancers were attributable to overweight and obesity, 5–9% of activity-related cancers were attributable to physical inactivity, and 1–6% of alcohol-related cancers were attributable to alcohol consumption.
While these studies represent a valuable contribution to the literature, those previous estimates predicted the burden of cancer over finite periods of time extending into the future. An alternative approach, the future excess fraction (FEF) method, estimates the excess number of exposure-related cancers occurring over the lifetime of a population . The FEF method is an extension of the lifetime risk approach and uses a life table to account for competing risks. This method provides an estimate of the proportion of future cancers in those members of a cohort who were exposed in a given year, and enables estimation of the future burden of cancer under current and hypothesised future scenarios .
The current study aims to estimate the future number of cancers resulting from recent levels of exposure to a comprehensive list of 23 modifiable lifestyle, environmental, and occupational risk factors.