Melbourne School of Population and Global Health - Theses
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ItemTrends and Inequalities in Cancer Survival in Victoria, Australia( 2020)Background: Cancer is the second-highest cause of mortality worldwide, accounting for 9.6 million deaths in 2017, and its burden on individuals, economy and health system is a global problem. Although Australia has a universal health-care system, cancer survival varies by socio-economic disadvantage. The magnitude and age-related patterns of these inequalities are not clear in Victoria, Australia and little is known about whether the gap in cancer survival is narrowing or widening over time. Despite strong evidence that sex is associated with the incidence and prognosis of several diseases, few studies have assessed differences in cancer survival by sex, and no Australian study has comprehensively evaluated the magnitude and temporal and age-related patterns of differences in cancer survival by sex. This thesis aimed to investigate inequalities and trends in cancer patient survival by sex, area-level socio-economic disadvantage and remoteness of residence and identify the underlying causes of socio-economic inequality in colon cancer survival. Methods: Six studies were designed and conducted to address the aims of this thesis. The first study was a systematic review of peer-reviewed published articles since 2005 that attempted to identify the underlying reasons for socio-economic inequalities in cancer survival. The second study was a systematic review of peer-reviewed published articles that assessed the association of rural-urban residence with cancer survival in high-income countries and summarised the current evidence in relation to potential contributing factors to the observed differences in survival between rural and urban regions. Studies 3, 4 and 5 used the Victorian Cancer Registry data to assess differences in cancer patient survival by sex, area-level socio-economic disadvantage and remoteness of residence. Study 6 used population-based linked health data to identify factors explaining socio-economic inequalities in colon cancer survival. Net survival was estimated using the Pohar-Perme method. Inequalities in survival were modelled using Poisson regression to estimate excess mortality rate ratios. Interventional causal mediation analysis was used to assess the underlying reasons for socio-economic inequalities in colon cancer survival. Results: Findings from the first systematic review suggest that socio-economic inequalities in cancer survival appear to be partly explained by differences in disease stage, health-related behaviours, co-morbidities and treatment modalities. The second review shows that rural cancer patients generally have worse survival compared with their urban counterparts. The underlying reasons for survival disadvantage for rural patients are not well known, but possible contenders include differences in lifestyle behaviour, stage of cancer at diagnosis, co-morbid conditions, and treatment modalities. Findings from analysing the Victorian Cancer Registry data suggest that cases living in more socio-economically disadvantaged areas or outside major cities generally had lower five-year survival than their counterparts living in less disadvantaged regions or major cities. In addition, men showed lower survival from most cancers than women. The observed socio-economic inequalities for colon cancer survival were not explained by variations in stage at diagnosis or surgery. Not receiving chemotherapy within 8 weeks after surgery, emergency admission prior to diagnosis and receiving surgery at a public hospital appeared to partly contribute to lower survival for men with stage III colon cancer living in the most disadvantaged areas, although this observation might be due to unmeasured characteristics of disadvantaged men receiving surgery in public hospitals rather than public/private hospitals themselves. Conclusions: This thesis has shown that inequalities in cancer patient survival by sex, area-level socio-economic disadvantage and remoteness of residence exist and have persisted over time, even though Australia has a universal health care system. Monitoring the magnitude of these inequalities and conducting high-quality research to identify the underlying reasons for inequalities in cancer survival is important to prioritise actionable factors to improve cancer outcomes for all patients.