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Background: The aim of this study was to determine the prognostic value of embryonic origin in patients undergoing resection after chemotherapy for colon cancer liver metastases (CCLM). Methods: We identified 725 patients with primary colon cancer and known RAS mutation status who underwent hepatic resection after preoperative chemotherapy for CCLM (1990 to 2015). Survival after resection of CCLM from midgut origin (n = 238) and hindgut origin (n = 487) was analyzed. Predictors of pathologic response and survival were determined. Prognostic value of embryonic origin was validated with a separate cohort of 252 patients with primary colon cancer who underwent resection of CCLM without preoperative chemotherapy. Results: Recurrence-free survival (RFS) and overall survival (OS) after hepatic resection were worse in patients with midgut origin tumors (RFS rate at 3 years: 15% vs 27%, P < 0.001; OS rate at 3 years: 46% vs 68%, P < 0.001). Independent factors associated with minor pathologic response were midgut embryonic origin [odds ratio (OR) 1.55, P = 0.010], absence of bevacizumab (OR 1.42, P = 0.034), and mutant RAS (OR 1.41, P = 0.043). Independent factors associated with worse OS were midgut embryonic origin [hazard ratio (HR) 2.04, P < 0.001], carcinoembryonic antigen value ≥5 ng/ mL at hepatic resection (HR 1.46, P = 0.0021), synchronous CCLM (HR 1.45, P = 0.012), and mutant RAS (HR 1.43, P = 0.0040). In the validation cohort, patients with CCLM of midgut origin had a worse 3-year OS rate (55% vs 78%, P = 0.003). Conclusions: Compared with CCLM from hindgut origin, CCLM from midgut origin are associated with worse pathologic response to chemotherapy and worse survival after resection. This effect appears to be independent of RAS mutation status. [ABSTRACT FROM AUTHOR]

Competing Interests: Conflicts of Interest and Source of Funding: None.