Background: Although the prognostic role of surgical margin status after resection of colorectal liver metastasis (CRLM) has been previously examined, controversy still surrounds the importance of surgical margin status in patients with multiple tumors. Methods: Patients who underwent curative-intent surgery for CRLM from 2000 to 2015 and who presented with multiple tumors were identified. Patients with R1 resection status determined by the closest resection margin of the non-largest tumor were classified as R1-Type 1; patients with R1 status determined by the resection margin of the largest tumor were defined as R1-Type 2. Data regarding surgical margin status, size of tumors, and overall survival (OS) were collected and assessed. Results: A total of 251 patients met inclusion criteria; 156 patients (62.2%) had a negative margin (R0), 50 had an R1-type 1 (19.9%), and 45 had an R1-type 2 (17.9%) margin. Median and 5-year OS in the entire cohort was 56.4 months and 48.0%, respectively. When all R1 (Type 1 + Type 2) patients were compared with R0 patients, an R1 was not associated with worse prognosis (P = 0.05). In contrast, when R1-type 2 patients were compared with R0 patients, an R1 was strongly associated with worse OS (P = 0.009). On multivariate analysis, although the prognostic impact of all R1 was not associated with OS (hazard ratio [HR] 1.56; P = 0.08), R1-Type 2 margin status independently predicted a poor outcome (HR 1.93; P = 0.03). Conclusions: The impact of margin status varied according to the size of the tumor assessed. While R1 margin status defined according to the non-largest tumor was not associated with OS, R1 margin status relative to the largest index lesion was associated with prognosis.
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