Oncologic Impact of Margin-to-Size Ratio for Intrahepatic Cholangiocarcinoma

BACKGROUND: The optimal surgical margin width for intrahepatic cholangiocarcinoma (ICC) remains uncertain. We hypothesized that the oncologic benefit of a wide margin may be modulated by tumor-related factors. STUDY DESIGN: Patients who underwent curative-intent liver resection for solitary ICC were identified from a large, international multi-institutional database. A novel metric, the margin-to-size ratio (MSR), was defined as the ratio of surgical margin width (mm) to tumor size (mm), integrating both parameters into a single variable. Multivariable Cox regression models were used to evaluate the association between MSR and recurrence-free survival (RFS). RESULTS: Among 1,172 patients, the median tumor size was 57.0 mm, the median margin width was 4.0 mm (interquartile range 1.0 to 10.0), and the median MSR was 0.07 (interquartile range 0.02 to 0.20). On multivariable analysis, a higher MSR was independently associated with improved RFS (hazard ratio 0.59, 95% CI 0.36 to 0.96, p = 0.033), whereas neither absolute margin width nor R1 resection status was associated with RFS. Using maximally selected rank statistics, an MSR threshold of 0.142 was identified. Patients with a high MSR (0.142 or more) had superior 3-year RFS compared with individuals with a low MSR (less than 0.142; 55.7% [95% CI 46.0 to 67.6] vs 45.2% [95% CI 38.0 to 53.8]; p = 0.016). CONCLUSIONS: MSR was independently associated with RFS after ICC resection, whereas conventional margin metrics, including absolute margin width and R1 resection status, were not associated with RFS. MSR may provide a clinically interpretable framework to contextualize margin adequacy relative to tumor size and inform individualized decision-making.