Elsevier

Preventive Medicine

Volume 122, May 2019, Pages 9-19
Preventive Medicine

Estimates of the current and future burden of cancer attributable to active and passive tobacco smoking in Canada

https://doi.org/10.1016/j.ypmed.2019.03.015Get rights and content

Highlights

  • 17.5% of cancers diagnosed in Canada in 2015 were attributable to tobacco smoking.

  • 0.8% of cancers diagnosed in Canada in 2015 were attributable to passive tobacco smoke exposure.

  • Over 70% of lung cancer was attributable to tobacco smoking.

  • Over 50,000 cases of cancer could be prevented by 2042 by reducing the prevalence of tobacco smoking by 50%.

Abstract

Although previous studies have examined the burden of cancer attributable to tobacco smoking, updated estimates are needed given the dramatic changes in smoking behaviours over the last 20 years. In this study, we estimate the proportion of cancer cases in 2015 attributable to past tobacco smoking and passive exposure in Canada and the proportion of cancers in the future that could be prevented through the implementation of interventions targeted at reducing tobacco use. Data from the Canadian Community Health Survey (2003) were used to estimate the prevalence of active tobacco smoking and passive exposure. Population attributable risk estimates were employed to estimate the proportion of cancers attributable to tobacco in 2015. The prevalence of active tobacco smoking and passive exposure was projected to 2032 and cancer incidence was projected from 2016 to 2042 to estimate the future burden of cancer attributable to tobacco. In 2003, 30% and 24% of Canadians were former and current smoker, respectively and 24% had been exposed to tobacco smoke in the past. We estimated that 17.5% (32,655 cases; 95% CI: 31,253–34,034) of cancers were attributable to active tobacco smoking and 0.8% (1408 cases; 95% CI: 1048–1781) to passive tobacco exposure in never smokers. Between 41,191 and 50,696 cases of cancer could be prevented by 2042 under various prevention scenarios. By decreasing passive tobacco exposure by 10–50%, between 730 and 3650 cancer cases could be prevented by 2042. Strategies focused on reducing the prevalence of tobacco smoking are crucial for cancer control in Canada.

Introduction

In 1986, the International Agency for Research on Cancer (IARC) determined that there was sufficient human evidence to classify tobacco smoking and second-hand smoke as carcinogenic to humans (Group 1) (International Agency for Reseach on Cancer Working Group on the Evaluation of Carcinogenic Risks to Humans, 1986). The IARC working group concluded that tobacco smoking is associated with cancers of the lung, oral cavity, larynx, esophagus, bladder and pancreas. Cancers of the stomach, paranasal sinus, nasopharynx, liver, kidney, ureter, uterine cervix, ovary, colorectum and myeloid leukemia have since been added to the list in subsequent IARC monographs (International Agency for Reseach on Cancer (IARC), 2012; International Agency for Research on Cancer (IARC), 2004). A recent large meta-analysis showed that active tobacco smoking is also associated with breast cancer (Macacu et al., 2015). In addition, IARC concluded that there is sufficient evidence that secondhand smoke exposure (i.e. passive smoking) causes lung cancer (International Agency for Reseach on Cancer (IARC), 2012). Since the most recent IARC monograph on tobacco use in 2012, large meta-analyses have shown that secondhand smoke exposure (i.e. passive tobacco exposure) is also associated with an increased risk of colorectal, breast and cervical cancers (Macacu et al., 2015; Yang et al., 2016; Zeng et al., 2012).

There are many complex biological mechanisms hypothesized that link tobacco smoke to cancer. The most widely accepted mechanism involves the binding of inhaled carcinogens to DNA and forming DNA adducts, which in turn can cause miscoding and permanent mutations. These mutations can cause the loss of normal cell proliferation and lead to cancer when mutations occur in oncogenes or tumor suppressor genes (International Agency for Reseach on Cancer (IARC), 2012).

In 2012, an estimated 45,464 deaths from all causes in Canada were attributable to smoking tobacco and the total costs of tobacco use were $16.2 billion, including both direct and indirect health care costs (Dobrescu et al., 2017). Given these statistics, reducing the prevalence of smoking through prevention strategies should be a top priority for public health agencies. Previous analyses conducted in the United Kingdom (Parkin, 2011), Australia (Pandeya et al., 2015) and globally (Reitsma et al., 2017) have estimated the burden of cancer attributable to smoking tobacco. In addition, previous estimates for Canada and the provinces of Ontario and Alberta estimated that 15–16% of cancer is attributable to tobacco smoking (Cancer Care Ontario, 2014; Krueger et al., 2016; Poirier et al., 2016). However, current detailed estimates for Canada and individual provinces are not available. Previous studies did not estimate the proportion of cancer that could be prevented in the future with reductions in smoking prevalence.

Given the strong, consistent relationships between active and passive tobacco smoking and the associated cancer sites, we aimed to estimate the proportion of incident cancer cases in 2015 that can be attributed to past tobacco exposure in Canada (attributable burden). We also estimated the proportion of cancers in the future (to 2042) that could potentially be prevented through the implementation of one of several intervention scenarios targeted at reducing the prevalence of active tobacco smoking and passive exposure (avoidable burden).

Section snippets

Methods

The detailed methodological framework for the current study was previously published (Brenner et al., 2018). A brief overview of the methods is included in this supplement. To estimate the attributable and avoidable burden of cancer in Canada, three measures of data were required: 1) risk estimates (i.e. relative risks, RRs) for the association between smoking and each cancer, 2) the prevalence of active tobacco smoking and passive exposure in Canada and provinces, and 3) age- and sex-specific

Prevalence of tobacco exposure

Based on results from the 2003 CCHS survey, an estimated 24.1% of Canadians were current smokers and 29.5% were former smokers (Table 2). The unadjusted prevalence of current smokers was higher for men (26.6%) than women (21.7%). This difference in rates by sex was also true for former smokers, where the prevalence was 33.3% and 25.8% for men and women, respectively. The prevalence of former smoking increased by age group ranging from 15.8% in those aged 20–34 years to 42.7% in those aged

Discussion

Our results suggest that of cancers diagnosed in 2015 associated with active tobacco smoking and passive exposure, 29.4% (32,655 cases) were attributable to active tobacco smoking and 2.7% (1408 cases) were attributable to passive tobacco exposure in never smokers. These estimates correspond to 17.5% and 0.8% of all cancers diagnosed in 2015, respectively. Of the 33,672 cancer cases attributable to tobacco exposure, more than half (18,549) were lung cancer cases. Other than cancer sites

Acknowledgments

We gratefully acknowledge the statistical work completed by Farah Khandwala. Darren Brenner was supported by a Canadian Cancer Society Capacity Development Award in Cancer Prevention and Christine Friedenreich was supported by a Health Senior Scholar Award from Alberta Innovates and an Alberta Cancer Foundation Weekend to End Women's Cancers Breast Cancer Chair.

Funding sources

This research is supported by the Canadian Cancer Society Partner Prevention Research Grant (grant #703106).

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    Additional members of the ComPARe Study Team: Eduardo Franco, Gerald Bronfman Department of Oncology, Division of Cancer Epidemiology and Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada; Will King, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada; Paul Demers, Occupational Cancer Research Centre, Toronto, Ontario, Canada; Prithwish De, Cancer Care Ontario, Toronto, Ontario, Canada; Leah Smith, Canadian Cancer Society, Toronto, Ontario, Canada; Elizabeth Holmes, Canadian Cancer Society, Toronto, Ontario, Canada; Dylan O'Sullivan, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada; Karena Volesky, Gerald Bronfman Department of Oncology, Division of Cancer Epidemiology and Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montréal, Québec, Canada; Zeinab El-Masri, Cancer Care Ontario, Toronto, Ontario, Canada; Robert Nuttall, Health Quality Ontario, Toronto, Ontario, Canada; Mariam El-Zein, Gerald Bronfman Department of Oncology, Division of Cancer Epidemiology McGill University, Montréal, Québec, Canada; Sheila Bouten, Department of Oncology, McGill University, Montréal, Québec, Canada; Tasha Narain, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada; Priyanka Gogna, Department of Public Health Sciences, Queen's University, Kingston, Ontario, Canada.

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