The mediating role of new morbidities on social inequality in mortality after curative cancer treatment - a SEQUEL study.

Background: Socioeconomic factors are linked to cancer survival. While cancer stage and treatment mediate this association, the role of new morbidities after cancer treatment is less understood. We investigated educational disparities in cancer mortality and whether it is explained by differences in death from new morbidities.

Methods: 85,849 cancer survivors with lung, breast, prostate, colorectal cancers were included. Follow-up for overall and cause-specific death began one year after diagnosis, lasting up to 16 years. Cox proportional hazard models estimated the association between education and death. Mediation analyses explored whether new morbidities mediated this association.

Results: Survivors with short education had higher mortality, particularly after breast and colon cancers, with a significant proportion of deaths due to new morbidities (breast cancer e.g. new primary cancers (HR 1.59, 95% CI:1.35,1.87), kidney and urinary problems (HR 4.16, 95% CI:1.24,13.97), and chronic respiratory issues (HR 2.99, 95% CI:1.86-4.79). Similar trends were observed in colon cancer survivors e.g. ischemic heart disease (HR 1.70, 95% CI:1.13,2.56) and heart failure (HR 3.53, 95% CI:1.35,9.19). Although some new morbidities were statistically significant mediators, they accounted for only a small proportion of the effects.

Conclusions: Educational disparities persist in cancer survivorship, with new morbidities contributing to higher mortality rates among survivors with shorter education.