Projections of smoking-related cancer mortality in Australia to 2044

Projections of mortality rates for cancers related to smoking

For both men and women, the age-standardised mortality rates for all smoking-related cancers combined are projected to decline continuously over the period 2015–2019 to 2040–2044, from 114.1 to 84.8 per 100 000 men and 76.5 to 57.8 per 100 000 women (figure 1 and table 1). For both men and women, the mortality rates are consistently lowest (<15 per 100 000) for those aged less than 55 years. The mortality rates for men in the older age groups showed a steady decline from the mid-1980s. Different patterns were observed for women, with lower rates overall and the decline occurring at a slower pace and starting later than was observed for men (figure 1). The decline in the mortality rate for women aged 55–64 years began in the 1990s, but for women in the older age groups (65 years and above) the decline began 5–20 years later.

Figure 1Figure 1Figure 1

Observed and projected age-standardised mortality rates for smoking-related cancers by age group and sex in Australia, 1970–2044. All rates are age-standardised to 2001 Australian population. The shaded area represents the 95% confidence interval.

Table 1

Observed and predicted age-standardised mortality rates and numbers of deaths (with 95% confidence intervals) from all smoking-related cancers combined by sex and 5 year period, 2015–2044

Despite the decreasing mortality rates, due to population growth and ageing, the overall number of smoking-related cancer deaths is projected to increase by 31.8% (28.7% for men and 35.8% for women) from 138 707 (77 839 men and 60 868 women) in 2015–2019 to 182 819 (100 153 men and 82 666 women) in 2040–2044 (table 1).

Estimated number of cancer deaths directly attributable to smoking

Figure 2 shows the total estimated numbers of cancer deaths directly attributable to smoking by age group and sex for people aged 35 years and above in Australia in 2000–2044. For both men and women, the numbers of cancer deaths directly attributable to smoking for the youngest age group (35–54 years) are consistently low (≤11% of the total), and the numbers of cancer deaths directly attributable to smoking for the 55–64 and 65–74 year age groups showed a steady decline over the projection period 2020–2044. In contrast to the younger age groups, the numbers of cancer deaths directly attributable to smoking for those aged 75 years and above are expected to continue to increase to 2044. We estimate that in Australia over the period 2020–2044, there will be 254 583 cancer deaths (173 943 men and 80 640 women) directly attributable to smoking, representing 32.3% (37.2% for men and 25.2% for women) of the total deaths from cancers, which are known to be related to smoking (table 2). Lung cancer is estimated to remain the cancer type with the largest number of deaths directly attributable to smoking, accounting for 61.7% of the total cancer deaths directly attributable to smoking in 2020–2044 (figure 3 and table 2). For every smoking-related cancer type, the SAF decreased over the period 2000–2044 (table 2). Cancer types with the largest SAFs for the period 2020–2044 are cancers of the lung, larynx, oesophagus and oral cancers (comprising lip, oral cavity and pharynx).

Figure 2Figure 2Figure 2

Total numbers of cancer deaths directly attributable to smoking by age group and sex in Australia, 2000–2044.

Figure 3Figure 3Figure 3

Numbers of cancer deaths directly attributable to smoking by cancer type, sex and age group to 2044 in Australia, ranked by the number of cancer deaths directly attributable to smoking in 2015–2019.

Table 2

Observed and projected numbers of cancer deaths directly attributable to smoking and smoking attributable fraction by cancer type for people aged 35 years and above in 2015–2044 in Australia, ranked by the total number of cancer deaths directly attributable to smoking in 2015–2019

Discussion

Using Australia as an example of a high-income country with successfully implemented tobacco control initiatives, resulting in declining cigarette smoking and tobacco consumption, we have projected the future national burden of cancer deaths from smoking-related cancers. Our projections indicate that mortality rates for smoking-related cancers for both men and women in Australia are expected to continuously and gradually decline to 2044, to a large extent reflecting the success and velocity of past and current tobacco control measures. Despite these declining mortality rates, our results project that the overall number of deaths from smoking-related cancers are likely to increase by 32% over the period 2015–2019 to 2020–2044, as a result of the ageing population and increasing population size.

We estimate that there will be more than 250 000 cancer deaths directly attributable to smoking between 2020 and 2044, accounting for one-third of the total number of deaths from smoking-related cancers. Fortunately, the number of cancer deaths directly attributable to smoking for people aged less than 75 years is expected to decrease over the 25 years to 2044. A decline in the proportion of deaths directly attributable to smoking was apparent overall and for each individual cancer type, although the SAFs were still high for cancers of the lung, larynx, oesophagus and oral cancers. Lung cancer is estimated to remain the leading cause of smoking-related cancer death in Australia and will account for 61.7% of the total estimated number of cancer deaths directly attributable to smoking over the period 2020–2044. Notably, cancer is only one of many health problems associated with tobacco smoking.17 19 The Australian Burden of Disease study estimated that cancer was responsible for ~56% of all deaths directly attributable to smoking in Australia in 2018,20 thus the total number of deaths directly attributable to smoking in Australia will be substantially greater than estimated in this work for cancer alone.

Given the strong association between smoking and lung cancer mortality,21 there has been increasing interest in incorporating information on smoking in lung cancer mortality projections.3 8 However, these methods have not been used for projecting mortality rates for all smoking-related cancer types. By grouping smoking-related cancer types together based on the proportion of cases currently attributable to smoking, we were able to include historical and current smoking patterns in the projection models for cancer types, which could not be individually fitted using such a model due to the small numbers of deaths.9 We confirmed that the models were reliable by providing validation of the 20-year projections using observed data. As there is a 26–33 year lag between changes in smoking behaviour and any subsequent impact on cancer mortality rates,3 our projections to 2044 are likely to be robust as they are based on past tobacco consumption up to 2019.

The successful implementation of a range of tobacco control programmes has been crucial in the reduction in smoking prevalence and cigarette consumption evident in many high-income countries, including Australia.22 23 The findings from this study confirmed that historical patterns in tobacco smoking are a strong predictor of mortality rates for smoking-related cancers.3 The earliest research that revealed the link between smoking and cancer was published in the 1950s4 5 and eventually initiated the introduction of tobacco control interventions internationally.3 4 In Australia, mandatory health warnings on all cigarette packs were first implemented in 1973, and all cigarette advertising on radio and television was banned in 1976 with more comprehensive advertising and promotion bans in subsequent decades.24 More recent tobacco control measures in Australia include media campaigns, plain packaging, a 25% increase in tobacco excise in 2010 and an annual 12.5% increase in tobacco excise implemented from 2013 to 2020.24 All these measures have resulted in decreases in the prevalence of smoking, beginning in the 1950s for Australian men and in the 1980s for Australian women.3

Despite the success of tobacco control in Australia, the most recently published estimates of smoking prevalence in Australia show that over 11% of Australians aged 18 years and over are daily smokers and that an additional 1% smoke less frequently (noting that these data have been collected during the COVID-19 pandemic and may not be directly comparable to previous estimates).25 Data have also shown considerable differences in smoking behaviour across sociodemographic groups in Australia, with higher smoking rates observed for those of lower socioeconomic status or with a lower level of education26 and also among Aboriginal and Torres Strait Islander peoples and other priority populations.27–29 The estimates presented demonstrate the effects of ‘business as usual’ and show that continuing current tobacco control efforts are likely to result in relatively slow declines in cancer rates and in increasing deaths over time. Without accelerated action, supported by adequate resources, it is expected that the positive effects of existing tobacco control measures will lessen over time.30 There are also concerns regarding the impacts of online promotion,22 31 and that electronic cigarettes (e-cigarettes) and other novel tobacco products may have an adverse impact on smoking initiation rates.32 It is, therefore, important to strengthen and implement even more effective tobacco control programmes as soon as possible. A comprehensive time series analysis of the effectiveness of tobacco control measures in Australia in 2008 concluded that the most effective population level interventions were price control through excise and hard-hitting mass media antismoking campaigns, with a synergistic benefit when used in tandem.33 Over the past decade, while excise has reached best-practice levels, there has been little or no commensurate investment in antismoking campaigns, other than targeted campaigns to tackle smoking by Aboriginal and Torres Strait Islander peoples.34

In this study, only cancer types which have been shown to have an established relationship with cigarette smoking were included,6 but it should be acknowledged that smoking may also increase mortality from cancers for which there is limited evidence that smoking is a risk factor.35 For example, previous studies reported that smokers diagnosed with prostate cancer have poorer survival outcomes than non-smokers,17 and it has also been reported that women who were smokers at the time of breast cancer diagnosis are more likely to develop systemic recurrence after surgery.36 In addition, smoking can decrease the effectiveness of many cancer treatments, so quitting smoking is likely to have a range of benefits for smokers who are diagnosed with cancer.37 Furthermore, as tobacco smoking is also known to increase the risk of developing many non-cancer diseases,38 which are not included in this study, the wider benefits from tobacco control on all deaths directly attributable to smoking will be even greater than we have estimated here.

While this study focused on the impact of changing patterns in smoking behaviour on cancer deaths in the future, it is also important to acknowledge that this is only one factor of many which are likely to contribute to the decrease in mortality rates for these cancer types. It is likely that changes in cancer screening and cancer management, and improvements in treatment are all playing a role in the estimated declines in mortality we have reported.39 Moreover, as the results from this study revealed that the proportion of cancer deaths directly attributable to smoking appears to have declined over time, interventions for other risk factors are also important, as is improving and implementing cancer screening and developing effective treatments, so that cancer mortality not attributable to smoking can also be reduced. As a substantial number of cancer deaths occur among former smokers, ongoing investment in the feasibility of targeted lung cancer screening will also be critical for at-risk former smokers.

As with all modelled projections, this study has some limitations, which should be considered when interpreting the results. The main limitation is that the projections are dependent on the assumptions made. The models did not include possible changes in other factors that can contribute to cancer mortality, including other risk factors, and cancer screening or treatment patterns.3 In practice, these effects could plateau as they either decrease or impact only a small proportion of cases, respectively, or in the case of new treatment availability, further reduce cancer mortality. Also, the projection models did not capture the impact of the recent COVID-19 pandemic, which led to disruptions in healthcare provision that may contribute to future excess deaths even for those who did not contract COVID-19.40 41 Estimating these impacts will be the subject of future work. Another limitation of this study is that the SAFs were based on adjusted relative risks from the CPS II, which may not be representative of the Australian population. However, results from a previous study suggest that the relative risk for all-cause mortality for current smokers from the large Australian 45 and Up Study is similar to those for cohorts in the USA.19 Despite these limitations, the study also has many strengths. Most notable are: the use of long-term high-quality observed data with population coverage10; the model design accounted for detailed data on cigarette tar consumption and the degree of association between cancer risk and smoking and the validation of the projections using observed data (online supplemental figure S3). The validated methods presented in this study can be applied to other countries to provide better estimates of cancer mortality related to smoking.

This is the first study to provide longer term national-level projections for the mortality rates for all smoking-related cancers taking into account detailed historical smoking intensity data. These projections for smoking-related cancers can serve as benchmarks against which to measure the impact of future cancer control initiatives, and these projections could also help inform health service planning to meet the future requirements for cancer care and treatment. Recognising that there are other, additional causes of mortality attributable to smoking, our research highlights the ongoing and future impact of smoking on the cancer burden, even in a country with major declines in smoking prevalence. Continued efforts in tobacco control remain an urgent public health priority.

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