Background: Each year, tobacco use causes an estimated 7 million deaths worldwide, including 2.5 million from cancer, resulting in substantial health and economic burdens. While the role of tobacco control in primary cancer prevention is well established, evidence on the impact of smoking cessation in secondary prevention (cancer screening) and tertiary prevention (cancer care) remains limited.

Objectives: Assessing the health and economic benefits of smoking cessation interventions across the three components of cancer prevention.

Methods: In collaboration with more than 80 scientists from 52 institutions worldwide, IARC led and contributed to a series of population-based, epidemiologic, and health-economic studies evaluating the impact of tobacco control policies and smoking cessation across the cancer prevention continuum. Analyses assessed effects at the population level in preventing future cancers (primary prevention), within lung cancer screening initiatives to enhance effectiveness and cost-effectiveness (secondary prevention), and after cancer diagnosis to improve survival and life-years gained (tertiary prevention). We used both publicly available data and individual-level data from prospective and retrospective cohort studies conducted by IARC and collaborators across five continents.

Results:
1) Primary prevention: Each year, an estimated 3.5 million new cancer cases and 2.5 million cancer deaths worldwide are attributable to tobacco smoking, with the highest burden in East Asia, accounting for approximately 25–30% of global tobacco-related cancer cases and deaths. Many of these cancers are preventable through full implementation of World Health Organization (WHO) tobacco control policies. Our estimates indicated that comprehensive implementation of WHO MPOWER measures could prevent approximately 3.5 million cancer cases in East Asia over the next 25 years.

2) Secondary prevention: The rollout of lung cancer screening (LCS) initiatives provides a unique opportunity to address tobacco use. In a U.S. modelling study, adding a smoking cessation intervention with modest (15%) effectiveness increased lung cancer deaths averted approximately sixfold and life-years gained about fourteenfold compared with screening alone. In a UK cost-effectiveness analysis, offering immediate smoking cessation as part of LCS, compared with usual care, was associated with a net monetary benefit of £2,198 per person.

3) Tertiary prevention: For some cancers (e.g. lung cancer), smoking status at diagnosis has a greater impact on prognosis than anatomical staging. Furthermore, smoking cessation after diagnosis reduced cancer mortality by 30–50% and was associated with 1.5-3 years increase in the median progression-free survival time across multiple cancers. In a UK cost-effectiveness analysis, offering smoking cessation services at the point of cancer diagnosis was cost-effective across cancer types, yielding a net monetary benefit ranging from £1,951 per person for lung cancer to £5,362 for kidney cancer.

Conclusions/Implications:  Tobacco control and smoking cessation deliver substantial health and economic benefits across the entire cancer prevention continuum, from reducing cancer incidence to improving screening effectiveness and survival after diagnosis. Integrating smoking cessation into lung cancer screening and routine oncology care substantially increases life-years gained and is highly cost-effective. These findings underscore the need for the systematic implementation of smoking cessation support as a core component of cancer prevention and care pathways worldwide.