Socioeconomic disparities in site-specific cancer incidence and mortality: Golestan cohort study

Socioeconomic inequalities are key contributors to cancer disparities. We explored the associations between individual-level socioeconomic status (SES) indicators (composite wealth score, educational attainment and rural/urban residence) and site-specific cancer incidence and mortality.

For this prospective study, we used data from 49 776 participants of the Golestan Cohort Study in northeastern Iran, enrolled in 2004-2008. Follow-up continued until first primary cancer diagnosis, death, loss to follow-up, or 31 March 2021. We used Cox proportional hazard regression models to estimate HRs and 95% CI, adjusted for several cancer risk factors and all SES indicators.

Over a 14-year median follow-up, the highest wealth score quartile, compared with the lowest, was associated with reduced oesophageal (HR=0.61; 95% CI 0.43 to 0.88) and gastric (HR=0.61; 95% CI 0.43 to 0.86) but elevated breast (HR=2.54; 95% CI 1.32 to 4.89) cancer incidence. The highest education level, compared with none, was associated with reduced oesophageal (HR=0.43; 95% CI 0.24 to 0.79), gastric (HR=0.54; 95% CI 0.35 to 0.84), hepatobiliary (HR=0.33; 95% CI 0.13 to 0.83) and lung (HR=0.44; 95% CI 0.20 to 1.00) cancer incidence. Urban residence was associated with decreased oesophageal (HR=0.63; 95% CI 0.44 to 0.90) but increased colorectal (HR=1.72; 95% CI 1.17 to 2.54), breast (HR=2.37; 95% CI 1.52 to 3.71), hepatobiliary (HR=1.70; 95% CI 1.00 to 2.87) and prostate (HR=2.60; 95% CI 1.24 to 5.45) cancer incidence. Cancer mortality analyses showed similar associations though a few results were not statistically significant due to small sample sizes.

Low wealth score, lack of formal education and rural residence were associated with disparate cancer incidence and mortality, particularly gastrointestinal cancers, in this predominantly rural population from a low- and middle-income country.