Socioeconomic disparities in head and neck cancer survival in Germany: a causal mediation analysis using population-based cancer registry data

Abstract

Purpose: Despite recent improvements in cancer treatment in Germany, a marked difference in cancer survival based on socioeconomic factors persists. We aim to quantify the effect of socioeconomic inequality on head and neck cancer (HNC) survival.

Methods: Information on 20,821 HNC patients diagnosed in 2009-2013 was routinely collected by German population-based cancer registries. Socioeconomic inequality was defined by the German Index of Socioeconomic Deprivation. The Cox proportional regression and relative survival analysis measured the survival disparity according to level of socioeconomic deprivation with respective confidence intervals (CI). A causal mediation analysis was conducted to quantify the effect of socioeconomic deprivation mediated through medical care, stage at diagnosis, and treatment on HNC survival.

Results: The most socioeconomically deprived patients were found to have the highest hazard of dying when compared to the most affluent (Hazard Ratio: 1.25, 95% CI 1.17-1.34). The most deprived patients also had the worst 5-year age-adjusted relative survival (50.8%, 95% CI 48.5-53.0). Our mediation analysis showed that most of the effect of deprivation on survival was mediated through differential stage at diagnosis during the first 6 months after HNC diagnosis. As follow-up time increased, medical care, stage at diagnosis, and treatment played no role in mediating the effect of deprivation on survival.

Conclusion: This study confirms the survival disparity between affluent and deprived HNC patients in Germany. Considering data limitations, our results suggest that, within six months after HNC diagnosis, the elimination of differences in stage at diagnosis could reduce survival inequalities.

Keywords: Causality; Head and neck cancer; Mediation analysis; Socioeconomic deprivation; Survival.

Fig. 1

Map of Germany with districts included in the analysis, colored according to their mean level of socioeconomic deprivation, 2009–2013. Quintiles are listed in ascending order according to deprivation (quintile five = most deprived)

Fig. 2

Directed Acyclic Graph (DAG) depicting the causal relationships between deprivation and survival status in HNC patients. Age, sex, and year of diagnosis were considered as baseline confounders

Fig. 3

Kaplan–Meier curves comparing survival between least and most socioeconomically deprived patients diagnosed with head and neck cancer in Germany, 2009–2013

Fig. 4

Effect of deprivation and mediators on odds of deaths at different times since head and neck diagnosis