The effect of socioeconomic status on survival from colorectal cancer in the Melbourne Collaborative Cohort Study

Previous research relating lower socioeconomic status (SES) with poorer survival from colorectal cancer has varied in adjustment for confounding factors and in the use of individual-level or aggregate-level indicators of SES. We investigated the effect of SES and country of birth on survival from colorectal cancers diagnosed in participants of the Melbourne Collaborative Cohort Study. A total of 526 colorectal cancer cases diagnosed since baseline were followed from diagnosis to 1 June 2006 or death. Information on tumour site and stage, and treatments given were obtained from systematic medical record review. SES at diagnosis was assigned using both an area-based measure of social disadvantage and individual level of educational attainment. Cox regression models were used to estimate hazard ratios associated with socioeconomic disadvantage, educational attainment, and country of birth. During an average follow-up of 5.6 years from diagnosis, 230 deaths occurred, 197 from colorectal cancer. After adjusting for age, sex, tumour stage, waist circumference and adjuvant chemotherapy and radiotherapy, the hazard ratios of dying from all causes and from colorectal cancer associated with living in the least disadvantaged areas compared with most disadvantaged areas were 0.73 (95% CI 0.53-1.00, p for trend = 0.06) and 0.80 (95% CI 0.57-1.12, p for trend = 0.22) respectively. Further adjustment for hospital case-load, tumour characteristics, and lifestyle factors did not change the estimates materially. Level of educational attainment and country of birth were not independent predictors of the risk of dying from colorectal cancer. Despite a universal health care system in Australia, socioeconomic inequalities in survival from colorectal cancer exist, and an enduring challenge is to ensure that improvements in colorectal cancer survival are shared equally across the population.