Is the Social Gradient in Net Survival Observed in France the Result of Inequalities in Cancer-Specific Mortality or Inequalities in General Mortality?

Abstract

Background: In cancer net survival analyses, if life tables (LT) are not stratified based on socio-demographic characteristics, then the social gradient in mortality in the general population is ignored. Consequently, the social gradient estimated on cancer-related excess mortality might be inaccurate. We aimed to evaluate whether the social gradient in cancer net survival observed in France could be attributable to inaccurate LT.

Methods: Deprivation-specific LT were simulated, applying the social gradient in the background mortality due to external sources to the original French LT. Cancer registries' data from a previous French study were re-analyzed using the simulated LT. Deprivation was assessed according to the European Deprivation Index (EDI). Net survival was estimated by the Pohar-Perme method and flexible excess mortality hazard models by using multidimensional penalized splines.

Results: A reduction in net survival among patients living in the most-deprived areas was attenuated with simulated LT, but trends in the social gradient remained, except for prostate cancer, for which the social gradient reversed. Flexible modelling additionally showed a loss of effect of EDI upon the excess mortality hazard of esophagus, bladder and kidney cancers in men and bladder cancer in women using simulated LT.

Conclusions: For most cancers the results were similar using simulated LT. However, inconsistent results, particularly for prostate cancer, highlight the need for deprivation-specific LT in order to produce accurate results.

Keywords: European deprivation index; France; cancer registries; excess mortality framework; simulated deprivation-specific life tables.

Figure 1

Difference in 5-year age-standardized net survival (ASNS) between patients living in least-deprived environment (Q1) and patients living in most-deprived environment (Q5) (i.e., 5-Year Deprivation Gap), estimated by non-parametric Pohar–Perme method, for men (a) and women (b), for each cancer site, according to main analyses, sensitivity analyses using English life tables (SA_Eng LT), and sensitivity analyses using EDP data (SA_EDP). ASNS: age-standardized net survival; CNS: central nervous system; EDI: European Deprivation Index; EDP: French permanent demographic sample [Echantillon Démographique Permanent]; ENT: ear, neck, throat (head and neck cancers); Q1: 1st quintile of the national distribution of EDI; Q5: 5th quintile of the national distribution of EDI; SA_EDP: sensitivity analyses based on EDP data; SA_Eng LT: sensitivity analyses based on English life tables.

Figure 2

Excess mortality hazard ratio (EHR) as a function of deprivation (EDI) according to main analyses, sensitivity analyses using English life tables, and sensitivity analyses using EDP data, for cancer sites for which all three analyses were concordant (same flexible model selected), and model selection showed an overall proportional effect of EDI on excess mortality hazard (independent of age and time of follow-up). EDI: European Deprivation Index; EDP: French permanent demographic sample [Echantillon Démographique Permanent]; EHR: excess mortality hazard ratio; ENT: ear, neck, throat (head and neck cancers); LT: life tables.

Figure 3

Excess mortality hazard ratio (EHR) between the 90th and the 10th percentile of the national distribution of EDI as a function of the time since cancer diagnosis, according to main analyses, sensitivity analyses using English life tables and sensitivity analyses using EDP data, for cancer sites for which all three analyses were concordant (same flexible model selected) and model showed an overall time-dependent effect of EDI on excess mortality hazard. For corpus uteri cancer, the effect of EDI on excess mortality was also age-dependent, therefore the results are presented for three values of age corresponding to the 25th, 50th, and 75th percentiles of the age distribution in the studied population with corpus uteri cancer. EDI: European Deprivation Index; EDP: French permanent demographic sample [Echantillon Démographique Permanent]; EHR: excess mortality hazard ratio; LT: life tables; p90, p10: 90th and 10th percentile of the national distribution of EDI.

Figure 4

Excess mortality hazard ratio (EHR) between the 90th and the 10th percentile of the national distribution of EDI, as a function of the time since cancer diagnosis according to main and sensitivity analyses, for cancer sites for which the effect of EDI was different according to the analysis (i.e., different models selected in the three analyses) and time-dependent. For melanoma in women, the effect of EDI on excess mortality was also age-dependent in the sensitivity analysis using English life tables, therefore results are presented for 3 values of age corresponding to the 25th, 50th and 75th percentiles of the age distribution in the studied female population with melanoma. EDI: European Deprivation Index; EDP: French permanent demographic sample [Echantillon Démographique Permanent]; EHR: excess mortality hazard ratio; LT: life tables; p90, p10: 90th and 10th percentile of the national distribution of EDI.

Figure 4

Excess mortality hazard ratio (EHR) between the 90th and the 10th percentile of the national distribution of EDI, as a function of the time since cancer diagnosis according to main and sensitivity analyses, for cancer sites for which the effect of EDI was different according to the analysis (i.e., different models selected in the three analyses) and time-dependent. For melanoma in women, the effect of EDI on excess mortality was also age-dependent in the sensitivity analysis using English life tables, therefore results are presented for 3 values of age corresponding to the 25th, 50th and 75th percentiles of the age distribution in the studied female population with melanoma. EDI: European Deprivation Index; EDP: French permanent demographic sample [Echantillon Démographique Permanent]; EHR: excess mortality hazard ratio; LT: life tables; p90, p10: 90th and 10th percentile of the national distribution of EDI.

Figure 5

Excess mortality hazard ratio (EHR) between the 90th and the 10th percentile of the national distribution of EDI, as a function of time since cancer diagnosis and according to the main and sensitivity analyses, for prostate cancer (discordant results between main and sensitivity analyses). EDI: European Deprivation Index; EDP: French permanent demographic sample [Echantillon Démographique Permanent]; EHR: excess mortality hazard ratio; LT: life tables; p90, p10: 90th and 10th percentile of the national distribution of EDI.