Prevalence and survival benefit of adjuvant chemotherapy in stage III colon cancer patients: Comparison of overall and age-stratified results by multivariable modeling and propensity score methodology in a population-based cohort.

BACKGROUND: Few population-based studies have assessed the effectiveness of adjuvant chemotherapy (ACT) in stage III colon cancer patients according to age. We sought to quantify the prevalence of ACT use and the absolute and relative survival benefit of ACT overall and by age in a population-based cohort.
METHODS: Stage III patients with adenocarcinoma of the colon identified by the Georgia Comprehensive Cancer Registry for the years 2000-07 were eligible (final N=3057). We utilized Poisson regression to obtain adjusted mortality rates (MR) and Cox proportional hazards models to obtain adjusted hazard ratios (HRs) for 5-year overall survival. We evaluated control of confounding by comparing HRs obtained via multivariable modeling (MM), propensity score weighting (PSW), and propensity score matching (PSM).
RESULTS: Just over one-third of colon cancer patients did not receive ACT, and the proportion increased with age. Overall, receipt of ACT conferred an absolute (MR difference [No ACT rate-ACT rate] 25.4 deaths/1000 person-years [py], 95% confidence interval [CI]: 19.1-32.7 deaths/1000 py) and relative (MM HR=0.67, 95% CI: 0.59-0.76) survival benefit. The survival benefit was demonstrated across age groups. MM and propensity score methods yielded highly similar HRs.
CONCLUSION: Unless contraindicated, efforts to ensure receipt of ACT for stage III colon cancer patients up to 84 years of age are needed to improve the prognosis of patients with node-positive disease.