Aim
To quantify the contributions of various prognostic factors to socioeconomic disparities in survival for colorectal cancer in a large Australian cohort.
Methods
The study cohort were participants (267,153) in the 45 and Up Study (recruited 2006-2009) who were subsequently diagnosed with colorectal cancer. Socioeconomic status (SES) was defined using the individual’s educational attainment and a neighbourhood measure based on place of residence. Study data were linked by the CHeReL with the NSW Cancer Registry, NSW Admitted Patient Data Collection, NSW Emergency Department Data Collection and death data (to 31 December 2015). Treatment information was obtained through record linkage with hospitals, and Medicare Benefits Schedule and Pharmaceutical Benefits Scheme claims supplied by the Department of Human Services. Hazard ratios (HRs) for colorectal cancer-specific mortality were estimated from Cox proportional hazards regression and proportions of socioeconomic differences explained by prognostic factors were quantified.
Results
1720 participants were diagnosed between recruitment and 31 December 2013: 1174 (68%) colon and 546 rectal cancers. Significant colon cancer survival differences were only observed for neighbourhood SES (p=0.033); 95% being explained by disease-related factors.
Differences in rectal cancer survival were greater with the highest risk of death for those with lowest SES compared with the highest (HR=3.72; 95%CI: 1.86-7.43, p=0.0013 for neighbourhood SES; HR=2.36; 95%CI: 1.44-3.54, p=0.0009 for individual SES). Neighbourhood SES differences were explained by patients’ characteristics (36%) and disease-related factors (28%). Patients’ characteristics, treatment- and disease-related factors explained 33%, 41% and 30% respectively of survival differences by individual SES. Inclusion of all significant prognostic factors explained 35% and 65% of the survival differences in neighbourhood- and individual- level SES respectively, but significant disparities remained.
Conclusions
Disease-related factors explained most of the socioeconomic survival disparities in colon cancer. However, substantial differences remained for rectal cancer after accounting for patients’-, treatment- and disease-related factors.