Use of mortality tables by level of deprivation in the study of social inequalities in cancer survival

Background: Previous studies have reported lower net survival probabilities for socioeconomically deprived patients, using non-deprivation specific lifetables. Not accounting for the social gradient in background mortality could potentially overestimate the effect of deprivation on net survival. The aim of this study was to estimate the impact of taking into account the social gradient of expected mortality in the general population on the study of the social gradient of survival of people with cancer. Methods: French cancer registry data was analyzed, with 190,902 incident cases of nineteen cancer sites between 2013 and 2015. Deprivation was measured using the European deprivation index (EDI). Net survival was estimated thanks to additive models with French lifetables stratified on deprivation level with the EDI, using the non-parametric Pohar-perme method and flexible excess hazard modelling with multidimensional penalized splines, firstly with non-specific lifetables then with the deprivation specific-lifetables. Results: A significant effect of EDI on excess mortality hazard (EMH) remained when using the deprivation-specific lifetables for colorectal, lung cancer and melanoma in both sexes, and esophagus, bladder, head and neck and liver cancer for men, and breast, cervix and uterine cancer for women. The only site where the effect of EDI on EMH was no longer significant when using deprivation-specific lifetables was prostate cancer. Conclusions: The use of deprivation-specific lifetables confirms the existence of a social gradient in cancer survival, indicating that these inequalities do not result from inequalities in background mortality. Development of such deprivation-specific lifetables for future years is crucial to understand mechanisms of social inequalities and work towards reducing the social burden.