The role of adjuvant radiation therapy in T4 nonrectal colon cancers.

553 Background: The standard treatment for non-metastatic locally advanced (T4M0) non-rectal colon cancer is surgical resection followed by adjuvant chemotherapy. There is strong rational for the use of post-operative radiation therapy (RT) in T4 tumors since negative margins are difficult to obtain. Despite promising single institutional studies, a phase III clinical trial closed early due to poor accrual. The efficacy of adjuvant RT in these patients remains unknown. We hypothesized that patients at lower risk of micro-metastases would benefit most from aggressive local treatment. Methods: Cases were extracted from the Surveillance, Epidemiology, and End Results (SEER) database. Inclusion criteria: T4-anyN-M0 non-rectal colon cancers, diagnosed between 1988 and 2010. Exclusion criteria: rectal tumors and cases lacking staging information. Endpoints: overall survival (OS) and cancer-specific survival. Analyses were based on the Kaplan-Meier method and Cox proportional hazard model. Results: A total of 36...