Background
In Poland, approximately 25% of adults smoke daily, contributing substantially to premature mortality. Robust estimates of the mortality benefits of smoking cessation are essential to inform evidence-based tobacco control policies and to support progress toward the tobacco endgame, defined as a smoking prevalence below 5%. In the absence of randomized controlled trials, causal inference methods applied to observational data offer an important alternative for evaluating the health impact of quitting smoking.

Objectives
To estimate the effect of smoking cessation on 12-year all-cause and cancer mortality among adults in Poland, overall and stratified by sex.

Methods
We emulated a target trial using data from the Polish Cohort Study (PONS), including 13,148 women and men enrolled in 2010. The analysis compared current smokers with former smokers at baseline. We estimated 12-year absolute risk differences (RDs) for all-cause and cancer mortality using pooled logistic regression models. To address confounding, models were weighted by the inverse probability of treatment, accounting for age, sex, marital status, education, alcohol consumption, smoking duration, and physical activity and inactivity. Cumulative incidence curves were constructed under hypothetical scenarios of continued smoking and smoking cessation. Sex-stratified analyses were conducted. Ninety-five percent confidence intervals (95% CIs) were obtained using bootstrapping.

Results
Among 2,482 current smokers and 4,258 former smokers, a total of 636 deaths occurred during follow-up, including 260 cancer-related deaths. The 12-year all-cause mortality risk was 12.6% (95% CI: 11.3–14.1) among current smokers and 7.8% (95% CI: 6.9–8.7) among former smokers, corresponding to an RD of −4.9 percentage points (95% CI: −6.7 to −3.3). The reduction in mortality risk was more pronounced in men (RD: −8.2 percentage points; 95% CI: −12.6 to −4.8) than in women (RD: −3.5 percentage points; 95% CI: −5.6 to −1.6). For cancer mortality, the 12-year risk was 5.7% (95% CI: 4.7–6.8) among current smokers and 3.1% (95% CI: 2.4–3.6) among former smokers, yielding an RD of −2.6 percentage points (95% CI: −4.0 to −1.4).

Conclusions/Implications
Smoking cessation is associated with a substantial absolute reduction in both all-cause and cancer mortality in Poland, with particularly strong benefits observed among men. These findings provide population-based causal evidence supporting intensified tobacco cessation policies as a key strategy to reduce premature mortality and to accelerate progress toward the tobacco endgame in Central and Eastern Europe.