The future excess fraction of cancer due to lifestyle factors in Australia

1

Introduction

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 [1] , with 145,000 cases estimated to have been diagnosed in 2020 [2] . A high proportion of these cancers are caused by exposure to lifestyle, and occupational factors [3] . 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 [4] . In Australia, previous studies have estimated that 32–44% of the cancer burden in a single year was attributable to lifestyle exposures 567 . This is comparable to estimates from other countries, including the United Kingdom (UK; 38% of cases in 2015) [8] , United States (US; 42% of cases in 2014) [9] , and Canada (41% of cases in 2012) [10] .

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 [11] . A growing body of work has estimated the future burden of cancer using various methods, including work in Canada [12] and the UK [13] . 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) 141516 . They found that smoking, overweight and obesity, and alcohol consumption contributed the highest number of cancers during that period [17] . 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) [1819] . 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 [20] . The FEF method is an extension of the lifetime risk approach [2122] 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 [20] .

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.