Biological Resectability in Colorectal Liver Metastases: A Nomogram-Based Continuous Risk Model to Define Borderline Disease.

BACKGROUND: Resectability in colorectal liver metastases (CRLM) is traditionally defined by technical feasibility; however, a biologically based definition of borderline resectable disease has not been established. We evaluated the prognostic impact of KRAS mutation and developed a model for biological risk stratification. METHODS: This multi-institutional retrospective study included 584 patients undergoing initial hepatectomy for CRLM. The impact of KRAS mutation was assessed according to primary tumor sidedness and tumor burden score (TBS). A nomogram predicting overall survival (OS) was constructed using independent prognostic factors and compared with established clinical risk scores. RESULTS: KRAS mutation was identified in 36.8% of patients and was associated with worse OS (median survival: 47.3 vs. 70.6 months, p = 0.0006) and recurrence-free survival. This adverse impact was observed in left-sided tumors but not in right-sided tumors. TBS stratified prognosis in KRAS wild-type but not in mutant cases, suggesting that tumor biology may outweigh morphology. A nomogram incorporating KRAS status, TBS, CA19-9, primary nodal status, and extrahepatic disease demonstrated improved discriminatory ability compared with conventional models and stratified recurrence patterns, including extrahepatic recurrence. CONCLUSIONS: The prognostic impact of KRAS mutation depends on tumor sidedness and is independent of tumor morphology. Our nomogram provides a continuous biological risk assessment and may facilitate biological risk stratification and support future refinement of the concept of biologically borderline resectable CRLM.