Chapter 3 The health effects of active smoking

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Kalitsis, L|Winnall, WR|Hurley, S|Greenhalgh, EM|Winstanley, MH. 3.5.8 Bowel (colorectal) cancer. In Greenhalgh, EM|Scollo, MM|Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne : Cancer Council Victoria; 2019. Available from https://www.tobaccoinaustralia.org.au/chapter-3-health-effects/3-5-other-cancers/3-5-8-bowel-cancer
Last updated: January 2025

3.5.8 Bowel (colorectal) cancer

The colon is the major part of the large intestine and its primary function is to absorb water from digested material. The rectum is the final portion of the large intestine, where faeces is stored before defecation through the anus. Risk factors for colorectal (bowel) cancer include age, tobacco use, alcohol consumption, obesity, poor diet, and physical inactivity.1

Colorectal cancer is common in Australia. In 2024, 15,542 people were diagnosed with colorectal cancer and 5,239 people died  from the disease.2,3 Colorectal cancer was estimated to be the fourth most common cancer diagnosis and the second most common cause of death from cancer.4 Australians with colorectal cancer have a 71% chance of surviving for five years or longer, based on data from the period 2016–2020.5 Over 90% of colorectal cancers are adenocarcinomas, with a number of other types being much rarer.1

Bowel cancer can make life difficult with symptoms including pain, diarrhoea, urgent bowel movements and bleeding from the anus. Side effects from treatment, such as chemotherapy and surgery to remove part of the bowel can also contribute to these problems.6

3.5.8.1 Risk associated with smoking

The 2014 US Surgeon General’s report concluded that smoking causes colorectal cancer. This report also stated that smoking causes colorectal adenomatous polyps, a non-cancerous condition that may develop into colorectal cancer.7 Several meta-analyses have concluded that smoking increases the risk of colorectal cancer by about 1.2-fold.8-13  Genetic studies have also indicated that the association of smoking and colorectal cancer is causal.14

Australians (aged 45 and over) who currently smoke have been found to have a 1.31-fold increased risk of colorectal cancer compared to those who do not smoke.15

Given the robust evidence that smoking causes colorectal cancer, recommendations have been made to lower the age that bowel cancer screening starts for people who smoke from 50 years to 45 years.16,17 As of 1 July 2024, all Australians aged 45–74 years are eligible for bowel cancer screening.18

3.5.8.2 How tobacco smoke causes bowel cancer

The evidence strongly suggests that smoking increases the formation of polyps, the precursor of colorectal cancer, and also possibly leads to the development of malignancy.7 Many carcinogens in cigarette smoke, such as PAHs, heterocyclic aromatic amines and N-nitrosamines can reach the bowel via the bloodstream. Higher concentrations of DNA adducts to metabolites of PAHs have been found in the bowel tissue of people who smoke compared to those who do not smoke.19 Some genetic studies have suggested that smoking causes DNA methylation, which inactivates genes involved cell division, DNA repair, programmed cell death, signal transduction and cell migration. Thereby, driving colorectal cancer.17,20 Animal studies have indicated that exposure to smoke increases the risk of colorectal cancer spreading to the lungs by increasing inflammation and changes to cell adhesion processes.21

3.5.8.3 Factors affecting risk

Intensity and duration of smoking

Two meta-analyses and a large prospective cohort study have reported that the risk of colorectal cancer increases with the amount smoked per day, pack-years of smoking and duration of smoking.8,10,22

Cancer type

Causal relationships with smoking appear to differ across different types of colorectal cancer. Some studies have found that the risk of colorectal cancer associated with smoking is greater for sub-types defined by anatomical location, phenotype and BRAF gene mutation status.12,17,23 A study comparing the risks of colorectal cancer from smoking and from genetics predicted that smoking was an independent risk factor for this cancer.24

Smoking cessation

People who formerly smoked generally have lower risk of colorectal cancer compared to those who currently smoke. A large US cohort analysis found that the risk of colorectal cancer decreases with time since cessation, with no association for those who had quit smoking before the age of 40, or for those who had quit smoking for 31 years or more.22 A subsequent meta-analysis of 14 prospective cohort studies found that smoking cessation was associated with improved chances of survival compared to those who currently smoked.25 The 2020 US Surgeon General’s report stated that smoking cessation reduces the risk of colorectal cancer.26

3.5.8.4 Impact of smoking on prognosis

People with colorectal cancer who smoke are more likely to have advanced disease than those who do not.27 Two meta-analyses investigating the link between smoking and death from colorectal cancer found that mortality rates are higher among those who smoke.8,10 A more recent meta-analysis from 2018 found that people who currently smoke have a 1.29-fold increased risk of death and people who formerly smoked have a 1.12-fold increased risk of death compared to people who never smoked.25 A small study of people with cancer of the anus found that recurrence rates and cancer-related deaths were higher in patients who continued to smoke after their diagnosis.28

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References

1. Australian Institute of Health and Welfare. Colorectal and other digestive-tract cancers.  Canberra: AIHW. 2018. Available from: https://www.aihw.gov.au/reports/cancer/colorectal-other-digestive-tract-cancers.

2. Australian Institute of Health and Welfare. Cancer data in Australia. Data tables: CDIA 2024: Book 1a – Cancer incidence (age-standardised rates and 5-year age groups) Canberra: AIHW. 2024. Available from: https://www.aihw.gov.au/reports/cancer/cancer-data-in-australia/data.

3. Australian Institute of Health and Welfare. Cancer data in Australia. Data tables: CDIA 2024: Book 2a – Cancer mortality (age-standardised rates and 5-year age groups) Canberra: AIHW. 2024. Available from: https://www.aihw.gov.au/reports/cancer/cancer-data-in-australia/data.

4. Australian Institute of Health and Welfare. Cancer data in Australia.  Canberra: AIHW. 2024. Available from: https://www.aihw.gov.au/reports/cancer/cancer-data-in-australia.

5. Australian Institute of Health and Welfare. Cancer data in Australia. Data tables: CDIA 2024: Book 3a – Cancer survival summary (observed, relative and conditional estimates) Canberra: AIHW. 2024. Available from: https://www.aihw.gov.au/reports/cancer/cancer-data-in-australia/data.

6. Cancer Council Australia. Understanding bowel cancer, 2023, Cancer Council Australia. Available from: https://www.cancer.org.au/assets/pdf/understanding-bowel-cancer-booklet.

7. US Department of Health and Human Services. The health consequences of smoking: 50 years of progress. A report of the Surgeon General.  Atlanta, GA: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health. 2014. Available from: https://www.ncbi.nlm.nih.gov/books/NBK179276/pdf/Bookshelf_NBK179276.pdf.

8. Botteri E, Iodice S, Bagnardi V, Raimondi S, Lowenfels AB, et al. Smoking and colorectal cancer: a meta-analysis. JAMA, 2008; 300(23):2765-78. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19088354

9. Huxley RR, Ansary-Moghaddam A, Clifton P, Czernichow S, Parr CL, et al. The impact of dietary and lifestyle risk factors on risk of colorectal cancer: a quantitative overview of the epidemiological evidence. International Journal of Cancer, 2009; 125(1):171-80. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19350627

10. Liang PS, Chen TY, and Giovannucci E. Cigarette smoking and colorectal cancer incidence and mortality: systematic review and meta-analysis. International Journal of Cancer, 2009; 124(10):2406-15. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19142968

11. Tsoi KK, Pau CY, Wu WK, Chan FK, Griffiths S, et al. Cigarette smoking and the risk of colorectal cancer: a meta-analysis of prospective cohort studies. Clinical Gastroenterology and Hepatology, 2009; 7(6):682-8 e1-5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19245853

12. Botteri E, Borroni E, Sloan EK, Bagnardi V, Bosetti C, et al. Smoking and Colorectal Cancer Risk, Overall and by Molecular Subtypes: A Meta-Analysis. American Journal of Gastroenterology, 2020; 115(12):1940-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/32773458

13. Keivanlou MH, Amini-Salehi E, Hassanipour S, Mahapatro A, Raghuma N, et al. Association between smoking and colorectal cancer in Eastern Mediterranean Regional Office (EMRO): A systematic review and meta-analysis. Saudi Journal of Gastroenterology, 2023; 29(4):204-11. Available from: https://www.ncbi.nlm.nih.gov/pubmed/37470665

14. Dimou N, Yarmolinsky J, Bouras E, Tsilidis KK, Martin RM, et al. Causal effects of lifetime smoking on breast and colorectal cancer risk: Mendelian randomization study. Cancer Epidemiology, Biomarkers and Prevention, 2021; 30(5):953-64. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33653810

15. Weber MF, Sarich PEA, Vaneckova P, Wade S, Egger S, et al. Cancer incidence and cancer death in relation to tobacco smoking in a population-based Australian cohort study. International Journal of Cancer, 2021; 149(5):1076-88. Available from: https://www.ncbi.nlm.nih.gov/pubmed/34015143

16. Acott A, Theus S, Marchant-Miros K, and Mancino A. Association of tobacco and alcohol use with earlier development of colorectal cancer: should we modify screening guidelines? American Journal of Surgery, 2008; 196(6):915–9. Available from: https://pubmed.ncbi.nlm.nih.gov/19095109/

17. Limsui D, Vierkant RA, Tillmans LS, Wang AH, Weisenberger DJ, et al. Cigarette smoking and colorectal cancer risk by molecularly defined subtypes. Journal of the National Cancer Institute, 2010; 102(14):1012-22. Available from: https://www.ncbi.nlm.nih.gov/pubmed/20587792

18. Australian Government Department of Health and Aged Care. National Bowel Cancer Screening Program. 2024. Available from: https://www.health.gov.au/our-work/national-bowel-cancer-screening-program.

19. Raimondi S, Botteri E, Iodice S, Lowenfels AB, and Maisonneuve P. Gene-smoking interaction on colorectal adenoma and cancer risk: review and meta-analysis. Mutation Research, 2009; 670(1-2):6-14. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19589345

20. Zhou X, Xiao Q, Jiang F, Sun J, Wang L, et al. Dissecting the pathogenic effects of smoking and its hallmarks in blood DNA methylation on colorectal cancer risk. British Journal of Cancer, 2023; 129(8):1306-13. Available from: https://www.ncbi.nlm.nih.gov/pubmed/37608097

21. Makino A, Tsuruta M, Okabayashi K, Ishida T, Shigeta K, et al. The impact of smoking on pulmonary metastasis in colorectal cancer. OncoTargets and Therapy, 2020; 13:9623-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33061444

22. Hannan LM, Jacobs EJ, and Thun MJ. The association between cigarette smoking and risk of colorectal cancer in a large prospective cohort from the United States. Cancer Epidemiology, Biomarkers and Prevention, 2009; 18(12):3362-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19959683

23. Boland CR and Goel A. Clearing the air on smoking and colorectal cancer. Journal of the National Cancer Institute, 2010; 102(14):996-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/20587791

24. Chen X, Jansen L, Guo F, Hoffmeister M, Chang-Claude J, et al. Smoking, genetic predisposition, and colorectal cancer risk. Clinical and Translational Gastroenterology, 2021; 12(3):e00317. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33646204

25. Ordonez-Mena JM, Walter V, Schottker B, Jenab M, O'Doherty MG, et al. Impact of pre-diagnostic smoking and smoking cessation on colorectal cancer prognosis: a meta-analysis of individual patient data from cohorts within the CHANCES consortium. Annals of Oncology, 2018; 29:472-83. Available from: https://www.ncbi.nlm.nih.gov/pubmed/29244072

26. US Department of Health and Human Services. Smoking cessation. A report of the Surgeon General.  Atlanta, GA U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Centre for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health  2020. Available from: https://www.cdc.gov/tobacco-surgeon-general-reports/reports/2020-smoking-cessation/.

27. Cebohin M, Samardzic S, Marjanovic K, Tot Vesic M, Kralik K, et al. Adenoma Characteristics and the Influence of Alcohol and Cigarette Consumption on the Development of Advanced Colorectal Adenomas. International Journal of Environmental Research and Public Health, 2020; 17(22). Available from: https://www.ncbi.nlm.nih.gov/pubmed/33182591

28. Ramamoorthy S, Luo L, Luo E, and Carethers JM. Tobacco smoking and risk of recurrence for squamous cell cancer of the anus. Cancer Detection and Prevention, 2008; 32(2):116-20. Available from: https://www.ncbi.nlm.nih.gov/pubmed/18639388

Intro
Chapter 2