?Background: Although more disadvantaged socioeconomic groups generally have higher smoking prevalence and incidence of smoking-related cancers than less disadvantaged groups, socioeconomic differences in the smoking-related cancer burden have not been quantified.

Objectives: To quantify the smoking-attributable cancer burden across socioeconomic strata in Australia and evaluate how socioeconomic differences in this burden have evolved over the past two decades.

Methods: We linked pooled individual-level data from seven Australian cohort studies (N=367,058) to national population-based cancer and death registries. We quantified the smoking-cancer association by area-based socioeconomic status (SES) using adjusted proportional hazards models. We estimated current and past adult smoking prevalence by SES from the Australian National Health Surveys 2001, 2004–2005, 2007–2008, 2011–2012, 2014–2015, 2017–2018, and 2022. We combined these estimates to calculate the population attributable fraction (PAF) of smoking-related cancers attributable to smoking, overall and by SES quintile, over time, accounting for competing risk of death. We also calculated 95% confidence intervals for differences in PAF estimates between SES quintiles.

Results: Daily smoking prevalence more than halved between 2001 and 2022 (22.4% to 10.6%), though declines were significantly faster in more advantaged socioeconomic groups. Currently, 28% (95% CI 26–30%) of smoking-related cancers in Australia are attributable to current and past smoking, down from 39% (95% CI 36–41%) 20 years ago. Of this total burden, current smoking now accounts for 16% (95% CI 15–18%), compared to 29% (95% CI 26–31%) 20 years prior. The smoking-attributable cancer burden follows a clear socioeconomic gradient, ranging from 39% in the most-disadvantaged quintile (Q1) to 30%, 29%, 22%, and 19% in the least-disadvantaged quintile (Q5). While all quintiles saw reductions from 20 years prior (Q1–Q5: 49%, 40%, 41%, 36%, 29%), contemporary inequities were more pronounced for current smoking. Specifically, the burden attributable to current smoking showed a four-fold disparity between the most and least disadvantaged groups (Q1–Q5: 28%, 19%, 15%, 11%, 7%), compared to a narrower range 20 years ago (Q1–Q5: 41%, 30%, 29%, 26%, 18%). While socioeconomic differences were previously confined to the extreme quintiles, contemporary data show significant inequities across nearly all strata. Notably, current smoking remains the primary driver of smoking-related cancer burden within the three most-disadvantaged quintiles, but is no longer the primary driver in the two least-disadvantaged quintiles. These differences are driven mainly by differences in smoking prevalence, with three times as many people currently smoking in the most-disadvantaged (18%) compared with the least-disadvantaged SES quintile (5%).

Conclusions: While national tobacco control strategies have successfully reduced the total smoking-related cancer burden, the slower rate of decline in low-SES populations has led to a relative increase in health inequity. Smoking-related cancer burden varies substantially by SES, with cancer burden attributable to current smoking now showing a stark four-fold disparity between the most-disadvantaged and the least-disadvantaged groups. Understanding the complex reasons behind higher smoking prevalence and smoking-attributable cancer burden in disadvantaged groups is crucial for effective intervention. Accelerated whole-of-population and priority population tobacco control is warranted, including that targeting those most in need, to address these widening inequities.