['Microscopic tumor involvement (R1) in different surgical resection margins after pancreaticoduodenectomy (PD) for pancreatic ductal adenocarcinoma (PDAC) has been debated.', 'Clinico-pathological data for 258 patients who underwent PD between 2001 and 2010 were retrieved from a prospective database. The rates of R1 resection in the circumferential resection margin (pancreatic transection, medial, posterior, and anterior surfaces) and their prognostic influence on survival were assessed.', 'For PDAC, the R1 rate was 57.1% (48/84) for any margin, 31.0% (26/84) for anterior surface, 42.9% (36/84) for posterior surface, 29.8% (25/84) for medial margin, and 7.1% (3/84) for pancreatic transection margin. Overall and disease-free survival for R1 resections were significantly worse than those for R0 resection (17.2 vs. 28.7 months, P\u2009=\u20090.007 and 12.3 vs. 21.0 months, P\u2009=\u20090.019, respectively). For individual margins, only medial positivity had a significant impact on survival (13.8 vs. 28.0 months, P\u2009<\u20090.001), as opposed to involvement in the anterior (19.7 vs. 23.3 months, P\u2009=\u20090.187) or posterior margin (17.5 vs. 24.2 months, P\u2009=\u20090.104). Multivariate analysis demonstrated R0 medial margin was an independent prognostic factor (P\u2009=\u20090.002, HR\u2009=\u20090.381; 95% CI 0.207-0.701).'] Does tumor infiltration in the medial resection margin predict survival after pancreaticoduodenectomy for pancreatic ductal adenocarcinoma?