The role of stage at diagnosis in colorectal cancer black-white survival disparities: a counterfactual causal inference approach

Abstract

Background

To date, a counterfactual framework has not been used to study determinants of social inequalities in cancer. Considering the case of colorectal cancer (CRC), for which racial/ethnic differences in stage at diagnosis and survival are well-documented, we quantify the extent to which black versus white survival disparities would be reduced had disparities in stage at diagnosis been eliminated in a large patient population.

Methods

We obtained data on CRC patients (diagnosed between 1992–2005 and followed until 2010) from US-SEER cancer registries. We employed a counterfactual approach to estimate the mean survival time up to the 60th month since diagnosis for black CRC patients had black-white disparities in stage at diagnosis been eliminated.

Results

Black patients survive approximately 4.0 (CI=4.6,3.2) months less than White patients within five years since diagnosis. Had disparities in stage at diagnosis been eliminated, survival disparities decrease to 2.6 (CI=3.4,1.7) months, a ~35% reduction. For patients diagnosed after the age of 65 disparities would be halved, while reduction of ~30% is estimated for younger patients. Survival disparities would be reduced by ~44% for women and ~26% for men.

Conclusions

Employing a counterfactual approach and allowing for heterogeneities in black-white disparities across patients’ characteristics, we give robust evidence that elimination of disparities in stage at diagnosis contributes to a substantial reduction in survival disparities in CRC.

Impact

We provide the first evidence in the SEER population that elimination of inequities in stage at diagnosis might lead to larger reductions in survival disparities among elderly and women.