Socioeconomic position and survival after lung cancer: Influence of stage, treatment and comorbidity among Danish patients with lung cancer diagnosed in 2004-2010

Background. To address social inequality in survival after lung cancer, it is important to consider how socioeconomic position (SEP) influences prognosis. We investigated whether SEP influenced receipt of first-line treatment and whether socioeconomic differences in survival could be explained by differences in stage, treatment and comorbidity. Material and methods. In the Danish Lung Cancer Register, we identified 13 045 patients with lung cancer diagnosed in 2004-2010, with information on stage, histology, performance status and first-line treatment. We obtained age, gender, vital status, comorbid conditions and socioeconomic information (education, income and cohabitation status) from nationwide population-based registers. Associations between SEP and receipt of first-line treatment were analysed in multivariate logistic regression models and those with overall mortality in Cox regression models with stepwise inclusion of possible mediators. Results. For both low-and high-stage lung cancer, adjusted ORs for first-line treatment were reduced in patients with short education and low income, although the OR for education did not reach statistical significance in men with high-stage disease. Patients with high-stage disease who lived alone were less likely to receive first-line treatment. The socioeconomic difference in overall survival was partly explained by differences in stage, treatment and comorbidity, although some differences remained after adjustment. Among patients with high-stage disease, the hazard ratio (HR) for death of those with low income was 1.12 (95% CI 1.05-1.19) in comparison with those with high income. Among patients with low-stage disease, those who lived alone had a 14% higher risk for dying (95% CI 1.05-1.25) than those who lived with a partner. The differences in risk for death by SEP were greatest in the first six months after diagnosis. Conclusion. Socioeconomic differences in survival after lung cancer are partly explained by social inequality in stage, first-line treatment and comorbidity. Efforts should be made to improve early diagnosis and adherence to first-line treatment recommendations among disadvantaged lung cancer patients.