title: How much do tumor stage and treatment explain socioeconomic inequalities in breast cancer survival? Applying causal mediation analysis to population-based data.
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.
authors.affiliation: Cancer Research UK Cancer Survival Group, Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK.
authors.forename: Ruoran
authors.initials: R
authors.lastname: Li
authors.affiliation: Department of Medical Statistics, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK.|Centre for Statistical Methodology, London School of Hygiene and Tropical Medicine, London, UK.
authors.forename: Rhian
authors.initials: R
authors.lastname: Daniel
authors.affiliation: Cancer Research UK Cancer Survival Group, Department of Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK. bernard.rachet@lshtm.ac.uk.|Centre for Statistical Methodology, London School of Hygiene and Tropical Medicine, London, UK. bernard.rachet@lshtm.ac.uk.
authors.forename: Bernard
authors.identifier: 0000-0001-5837-7773
authors.initials: B
authors.lastname: Rachet
mesh_terms: D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality* / Q000601:surgery; D016208:Databases, Factual; D004739:England / Q000453:epidemiology; D005260:Female; D054624:Health Status Disparities; D054625:Healthcare Disparities; D006801:Humans; D008875:Middle Aged; D009367:Neoplasm Staging; D011159:Population Surveillance; D012959:Socioeconomic Factors; D016019:Survival Analysis; D015996:Survival Rate
keywords: Breast cancer; Causal mediation; Population-based data; Socioeconomic inequalities; Surgical treatment; Survival; Tumour stage