Utilization of Adjuvant Radiotherapy for Resected Colon Cancer and Its Effect on Outcome

Adjuvant radiation is generally not recommended for colon cancer but may be considered in certain clinical scenarios [advanced local disease (pT4) and/or positive margins]. Guidelines in this area are lacking; thus we analyzed the National Cancer Database (NCDB) for patterns of care in this regard and any predictors for outcome.

We queried the NCDB from 2004 to 2016 for patients with resected adenocarcinoma of the colon having pT4 and/or had positive margins on final pathology and who received adjuvant multiagent chemotherapy. Multivariable logistic regression was used to identify predictors of adjuvant radiation. A propensity score was used to perform matched Kaplan-Meier analysis. Propensity-adjusted Cox regression was used to identify predictors of overall survival.

We identified 23,325 patients meeting criteria, of whom 1711 (7%) received adjuvant radiation. Median follow-up was 36 months. The majority of patients were pT4 alone (65%). Predictors of adjuvant radiation were lower comorbidity score, younger age, more remote year of treatment, and both pT4 and positive margins. Kaplan-Meier analysis revealed improved overall survival (OS) in patients with both pT4 and positive margins treated with radiation (median OS: 66 versus 47 months, p = 0.02). Receipt of adjuvant radiation was associated with improved OS [hazard ratio (HR): 0.86 (0.80-0.93) p = 0.0002] on Cox regression analysis. Increased age, higher comorbidity score, lower income, government insurance, and combined pT4/positive margins were indicative of worse survival.

Expectedly, adjuvant radiation use was relatively low but was associated with improved OS in patients with both pT4 and positive margins.