Oncologic outcomes according to the location and status of resection margin in pancreas head cancer: role of radiation therapy in R1 resection

PURPOSE: The clinical significance of margin status in pancreatic head cancer is still controversial due to the nonstandardized definition of R status and pathologic reporting. This study aims to evaluate the impact of the margin status including location and the role of radiation therapy in pancreatic head cancer. METHODS: A total of 314 patients who underwent curative-intent surgery for pancreatic head cancer between 2010 and 2017 were analyzed. Demographics, survival, and local recurrences were compared according to 2 definitions: 0-mm R1 as direct involvement and 1-mm R1 as close resection margin less than 1 mm. The specific margins were divided into 4 groups according to the location around the pancreas: pancreas transection, anterior surface, posterior surface, and vessel (superior mesenteric artery/superior mesenteric vein) margin. RESULTS: The 0-mm R1-rate was 15.6%, and increased to 36.3% in 1-mm R1. The median overall survival rate of 0-mm R0 vs. R1 was 26 months vs. 16 months (P = 0.052) and that of 1-mm R0 vs. R1 was 27 months vs. 18 months, respectively (P = 0.016). In individual margins, posterior, anterior surface, and pancreas transection margin involvement were associated with poor outcome, and the 1 mm posterior surface involvement was an independent risk factor for disease-free survival (hazard ratio, 1.63). Adjuvant radiation therapy had oncologic benefits, especially in R1 patients (P = 0.011) compared to R0 patients (P = 0.088). CONCLUSION: Margin status, especially 1-mm R1 status is an important predictive factor, and involved posterior surface has a clinical impact. Patients with positive margins should be considered adjuvant radiation therapy.