Abstract
Substantial socioeconomic inequalities in breast cancer survival persist in England, possibly due to more advanced cancer at diagnosis and differential access to treatment. We aim to disentangle the contributions of differential stage at diagnosis and differential treatment to the socioeconomic inequalities in cancer survival. Information on 36,793 women diagnosed with breast cancer during 2000–2007 was routinely collected by an English population-based cancer registry. Deprivation was determined for each patient according to her area of residence at the time of diagnosis. A parametric implementation of the mediation formula using Monte Carlo simulation was used to estimate the proportion of the effect of deprivation on survival mediated by stage and by treatment. One-third (35 % [23–48 %]) of the higher mortality experienced by most deprived patients at 6 months after diagnosis, and one tenth (14 % [−3 to 31 %]) at 5 years, was mediated by adverse stage distribution. We initially found no evidence of mediation via differential surgical treatment. However, sensitivity analyses testing some of our study limitations showed in particular that up to thirty per cent of the higher mortality in most deprived patients could be mediated by differential surgical treatment. This study illustrates the importance of using causal inference methods with routine medical data and the need for testing key assumptions through sensitivity analyses. Our results suggest that, although effort for earlier diagnosis is important, this would reduce the cancer survival inequalities only by a third. Because of data limitations, role of differential surgical treatment may have been under-estimated.Electronic supplementary materialThe online version of this article (doi:10.1007/s10654-016-0155-5) contains supplementary material, which is available to authorized users.
Highlights
Substantial socioeconomic inequalities in cancer survival have been observed in England for decades [1,2,3], meaning that many cancer deaths could be avoided [4]
Large deprivation gap existed for the short-term survival in the most advanced stage (IV), and in the long-term survival in the less advanced stages (II–III)
Our results are based on population-based data, i.e. on virtually all patients diagnosed with a breast cancer in a given region, including those who were diagnosed with advanced stage and those who were not optimally managed
Summary
Substantial socioeconomic inequalities in cancer survival have been observed in England for decades [1,2,3], meaning that many cancer deaths could be avoided [4]. Besides lower screening uptake and differential access to treatment, more advanced stage at diagnosis and severe comorbidity are regularly proposed as the most plausible explanatory factors of these inequalities [5, 6]. Using methods from the causal inference literature, we aim to disentangle the contributions of differential stage at diagnosis and differential treatment to the socioeconomic inequalities in cancer survival. To this end, we use population-based and routinely collected data for all patients diagnosed with a breast cancer within a defined area
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