BACKGROUND-AIM:
Tobacco use is linked to increased cancer risk, and people who smoke represent a large proportion of newly diagnosed patients with cancer. The fact that smoking cessation at the time of diagnosis can improve the patient’s life expectancy is still not broadly understood. We conducted a systematic review and meta-analysis to quantify the survival benefits obtainable by quitting smoking on diagnosis.

METHODS:
We included articles found in MEDLINE and EMBASE until 2 January 2024. We conducted a random effects meta-analysis, studying correlates of between-studies heterogeneity and exploring the presence of publication bias. We considered as eligible for inclusion only those articles in which the exposed group consisted of individuals who had ceased smoking either shortly (up to 1 month) before diagnosis or after it (eg, during treatment or follow-up). Consequently, we excluded studies that did not specify the time interval in which smoking cessation occurred.

RESULTS:
There were 36 eligible studies published in 1980-2023, totalling over 17000 actively smoking patients with cancer. The most studied cancer sites were the lung (n=17) and head and neck (n=14). The median proportion of patients who quit on diagnosis was 42.5%. Postdiagnosis cessation was associated with longer overall survival (summary HR (S(;)sHR) 0.71, 95% CI 0.65 to 0.78), progression-free survival (sHR 0.64, 95% CI 0.41 to 0.98), disease-free/recurrence-free survival (sHR 0.59, 95% CI 0.43 to 0.81) and improved local/locoregional control (sHR 0.69, 95% CI 0.50 to 0.94). Heterogeneity was generally large; for overall survival, study results were stronger when properly adjusted but did not vary across cancer sites. There was evidence for publication bias, but the results were only marginally altered on imputation of potentially missing studies.

LIMITATIONS:
Systematic differences between patients who quit versus continued smoking (eg, age, tumour stage) may bias the results if not adequately adjusted for in the analyses. Moreover, any prognostic factor that is linked with the likelihood of quitting (eg, pack-years, intensity of smoking, socioeconomic status) may act as a confounder and should be adjusted for in the analyses, but this was not the case for many included studies. Likewise, the impact of smoking cessation on the efficacy of subsequent or ongoing therapy was not systematically addressed, especially considering malignancies treated with targeted and immune therapy, alone or in combination. While we found no heterogeneity based on the cancer site and type, only a few studies focused on cancers other than of the lung and head and neck: this is currently a persistent knowledge gap that remains to be addressed.

CONCLUSIONS:
Postdiagnosis smoking cessation is effective in improving the chances of survival for patients with cancer. Cessation support programmes should be integrated into the routine management of patients with cancer as they may favourably affect survival.