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

Background: 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.

Methods: 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.

Results: 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.

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