Postoperative Radiation for Pathologic Stage T4 Colon Cancers Receiving Adjuvant Chemotherapy

Background: Previous small retrospective studies have suggested a benefit, mainly in preventing local recurrence, for postoperative radiation in nonmetastatic pathologic stage T4 colon cancers in patients who did not receive adjuvant chemotherapy. Current guidelines recommend postoperative radiation in nonmetastatic T4 colon cancers with penetration to a fixed structure, as well as for all patients with positive surgical margins. We aimed to assess the survival benefit of postoperative radiation in individuals with T4 colon cancers who received adjuvant chemotherapy. Methods: Using the National Cancer Data Base (2004-2014), we identified 20,967 and 5882 individuals with nonmetastatic pathologic stage T4 colon cancer treated with adjuvant chemotherapy who had negative or positive surgical margins, respectively. We used multivariate Cox regression to evaluate the effect of postoperative radiation on overall survival. In a secondary analysis, we stratified individuals according to chemotherapy intensity, pathologic N stage, and primary tumor location. Results: Postoperative radiation did not improve overall survival in individuals with positive surgical margins (hazard ratio = 1.05 [95% CI, 0.96-1.16]). This lack of survival benefit was noted regardless of chemotherapy regimen used, with adjusted hazard ratios of 1.11 (95% CI, 0.94-1.31) and 0.96 (0.85-1.09) for single-agent and doublet chemotherapy, respectively. Similarly, pathologic N stage and primary tumor location did not affect survival. In individuals with negative surgical margins, there was a detrimental effect for postoperative radiation, with an adjusted hazard ratio of 1.19 (95% CI, 1.10-1.29). Conclusion: Postoperative radiation did not improve overall survival in individuals with pathologic stage T4 colon cancer who had either negative or positive surgical margins and who received adjuvant chemotherapy.