Breast cancer is very common in Australia. In 2024, it was the second most diagnosed cancer, with 20,973 women and 221 men being diagnosed.1 Breast cancer accounts for around 28% of the cancers diagnosed among Australian women.2
Survival rates for breast cancer are relatively high, with 92% of people living for five years or longer after diagnosis based on data from the period 2016–2020.3 However, the high incidence means that the actual number of deaths from this disease is high. In 2024, an estimated 3,272 women and 33 men died from breast cancer.4
Known risk factors for breast cancer include age, genetic mutations, family or personal history of breast cancer, reproductive history, physical inactivity, obesity, alcohol consumption, and some hormone replacement therapies for menopause.5
Although breast cancer has a relatively high survival rate, for people diagnosed with late-stage disease, the survival rate is much lower. Treatments for breast cancer, including surgery, radiotherapy and chemotherapy can have difficult side effects.6
3.5.9.1 Risk associated with smoking
There is some evidence that smoking is associated with an increased risk of breast cancer, however whether smoking is a cause of breast cancer is currently unclear. The strength of the association between smoking and breast cancer risk is also unclear, due to inconsistencies between studies. Further, alcohol consumption is a known risk factor for breast cancer and many people who smoke also consume alcohol. Separating the risks of smoking from those of alcohol is difficult.7
In 2004, the IARC examined the risk of smoking in those who did not consume alcohol. After adjusting for many other factors such as age and family history of breast cancer, they concluded that there was no association between smoking and risk of breast cancer in women who did not consume alcohol.7
The 2014 US Surgeon General’s report also assessed the association between smoking and breast cancer incidence. The studies included were published between 2000 and 2011. For people who had ever smoked, there was a small (1.12-fold) increased risk of breast cancer. For current smoking, there was a 10% increased risk of breast cancer. People who smoked with higher intensity or duration had a slightly higher risk.8 The report concluded that the evidence is sufficient to identify mechanisms by which cigarette smoking may cause breast cancer. The evidence is suggestive but not sufficient to conclude that smoking causes breast cancer.8
A 2023 meta-analysis found that ever smoking, current smoking, and former smoking were associated with a 9%, 7%, and 8% increased risk of breast cancer respectively.9
Some recent genetic studies have indicated that smoking is a cause of breast cancer,10 and that lifetime smoking increases the risk of ER-positive, but not ER-negative, breast cancer.11 More data are required to validate these findings.
In 2011, a Canadian expert panel reviewed the evidence and concluded that smoking causes breast cancer and that the association between secondhand smoke exposure and breast cancer in young women is also consistent with causality.12 See Section 4.10.2 for further information on secondhand smoke exposure and breast cancer.
3.5.9.2 How tobacco smoke may cause breast cancer
There are biologically plausible mechanisms by which exposure to tobacco smoke could cause breast cancer. There are at least 20 known or suspected mammary carcinogens in tobacco smoke.12 DNA adducts (carcinogens bonded to DNA) from tobacco carcinogens are found in the breast fluid and breast tissue of people who smoke.8 The 2014 US Surgeon General’s report concluded that the available evidence supports biologically plausible mechanisms, particularly for DNA adduct formation and unrepaired DNA mutations, by which exposure to tobacco smoke could cause breast cancer. But this report also warned that the data are limited and a detailed mechanistic model cannot yet be assembled.8
3.5.9.3 Factors affecting risk
Smoking intensity and duration
The intensity and duration of smoking affects the strength of association with breast cancer. Those who smoked for 20 or more years, 20 or more cigarettes per day, or 20 or more pack-years have been shown to have a significantly increased risk of breast cancer by 13–16%, depending on the study.8 A 2023 meta-analysis strengthened these conclusions, finding that the risk of breast cancer increases linearly with smoking intensity. Compared to never smoking, smoking 20 cigarettes per day was associated with a 12% increase in risk while smoking 40 cigarettes per day was associated with a 26% increase. Similarly, 20 years of smoking was associated with an 5% increase in risk while smoking for 40 years was associated with an 11% increase.9
Menopause
There is emerging evidence that suggests premenopausal women may be at greater risk for breast cancer from smoking than postmenopausal women.8,13,14
3.5.9.4 Impact of smoking on prognosis
The 2014 US Surgeon General’s report highlighted the difficulty in inferring a causal association between smoking and breast cancer mortality; there are many confounding variables relating to treatment and other non-cancer, smoking-related comorbidities that can contribute to mortality. There is currently insufficient evidence to conclude that smoking or exposure to secondhand smoke influences breast cancer mortality.8
Since this report, a large meta-analysis, including over 400,000 women with breast cancer, found a 28% increase in mortality from breast cancer in those who currently smoke compared to those who never smoked. The mortality rates for those who formerly smoked were not significantly different to those who never smoked.15
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References
1. 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.
2. 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.
3. 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.
4. 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.
5. Centers for Disease Control and Prevention. Breast Cancer: What are the risk factors? 2024, US Department of Health & Human Services: USA. Available from: https://www.cdc.gov/breast-cancer/risk-factors/index.html.
6. Cancer Council Australia. Understanding breast cancer. 2024. Available from: https://www.cancer.org.au/assets/pdf/understanding-breast-cancer-booklet.
7. International Agency for Research on Cancer Working Group on the Evaluation of Carcinogenic Risks to Humans. Tobacco smoke and involuntary smoking. IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans. Volume 83. Lyon: International Agency for Research on Cancer. 2004. Available from: https://publications.iarc.fr/Book-And-Report-Series/Iarc-Monographs-On-The-Identification-Of-Carcinogenic-Hazards-To-Humans/Tobacco-Smoke-And-Involuntary-Smoking-2004.
8. 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.
9. Scala M, Bosetti C, Bagnardi V, Possenti I, Specchia C, et al. Dose-response relationships between cigarette smoking and breast cancer risk: A Systematic review and meta-analysis. Journal of Epidemiology, 2023; 33(12):640-8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/36967121
10. 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
11. Xu Z, Xu H, and Lu Y. Genetic liability to smoking and breast cancer risk. Clinical Epidemiology, 2020; 12:1145-8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/33116908
12. Johnson KC, Miller AB, Collishaw NE, Palmer JR, Hammond SK, et al. Active smoking and secondhand smoke increase breast cancer risk: the report of the Canadian Expert Panel on Tobacco Smoke and Breast Cancer Risk (2009). Tobacco Control, 2011; 20(1):e2. Available from: https://www.ncbi.nlm.nih.gov/pubmed/21148114
13. Penalver-Argueso B, Garcia-Esquinas E, Castello A, de Larrea-Baz NF, Castano-Vinyals G, et al. Smoking history and breast cancer risk by pathological subtype: MCC-Spain study. Tobacco Induced Diseases, 2023; 21:157. Available from: https://www.ncbi.nlm.nih.gov/pubmed/38034128
14. Wada K, Nagata C, Utada M, Sakata R, Kimura T, et al. Active and passive smoking and breast cancer in Japan: a pooled analysis of nine population-based cohort studies. International Journal of Epidemiology, 2024; 53(3). Available from: https://www.ncbi.nlm.nih.gov/pubmed/38604675
15. Sollie M and Bille C. Smoking and mortality in women diagnosed with breast cancer-a systematic review with meta-analysis based on 400,944 breast cancer cases. Gland Surgery, 2017; 6(4):385-93. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28861380