Explaining socio-economic differences in bladder cancer survival


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Beth Russell1,Mieke Van Hemelrijck1,Truls Gårdmark2,Lars Holmberg1,Pardeep Kumar3,Andrea Bellavia4,Christel Häggström5
1King's College London, London, UK,2Karolinska Institute, Stockholm, Sweden,3Royal Marsden NHS Foundation Trust, London, UK,4Havard T.H Chan School of Public Health, Boston, US,5Uppsala University, Uppsala, Sweden

Abstract

Background

There is increasing evidence that socioeconomic status (SES) may influence the survival of bladder cancer (BC) patients. However, the underlying mechanisms behind the proposed association are yet to be elucidated. Therefore, this novel study aims to disentangle the heterogeneity in the survival outcomes of different SES groups by identifying any potential mediators of the relationship.

Method

The Bladder Cancer Database Sweden (BladderBaSe) was used to select patients diagnosed between 1997 and 2014 with Tis/Ta-T4 disease. Education level was used as a proxy for SES. Accelerated failure time models were used to investigate the association between SES and survival. Mediation analysis, using the four-way decomposition method, was then conducted to assess the role of several potential mediators. The mediation analysis was then stratified by non-muscle invasive bladder cancer (NMIBC) and muscle invasive bladder cancer (MIBC) patients. All analyses were fully adjusted.

Results

37,755 patients were identified from BladderBaSe (74% NMIBC and 26% MIBC). Patients diagnosed with NMIBC and MIBC who had a medium/high SES were found to have a significantly increased overall and BC-specific survival when compared to those with a low SES. Optimal treatment was found to be a weak mediator in non-metastatic MIBC patients (2%). Age was found to mediate the relationship by 31%, and hospital type by 4% in the NMIBC patients only. The time from referral to transurethral resection of the bladder tumour (TURBT) was a considerable mediator (14%) in the MIBC patients only.

Conclusion

Mediation analysis suggested that the hypothesised relationship between SES and survival was contributed to by several factors with some being avoidable e.g. a delay in time between referral and TURBT, and patients receiving optimal treatment. Other factors such as age and hospital type are less manageable nevertheless highlight the importance of standardization of clinical care across SES groups.