BACKGROUND: A histologically involved surgical margin (R1) is often observed after resection for cholangiocarcinoma. Compared with a negative margin (R0), R1 with invasive carcinoma (R1inv) markedly worsens survival, whereas the prognostic effect of R1 with carcinoma in situ (R1cis) remains controversial. METHODS: Patients who underwent resection for perihilar cholangiocarcinoma between 2002 and 2019 were retrospectively reviewed. According to the pathological assessment, the duct margin was classified as R0, R1cis, or R1inv
radial margin positivity was treated as R1inv. Recurrence and survival were compared. RESULTS: Among the 681 patients, 457 had R0, 69 had R1cis, and 155 had R1inv. The overall five-year recurrence rate was 82.8 % with R1inv, 67.8 % with R1cis, and 47.6 % with R0 (P <
0.002)
the local recurrence rate also significantly differed among these groups (P <
0.002). The five-year survival rate was significantly worse with R1cis than with R0 (37.3 % vs. 56.7 %, P <
0.002) and better than that with R1inv (20.9 %, P = 0.007). Multivariate analysis revealed that R1cis was an independent predictor of survival (hazard ratio, 1.65
P <
0.002). CONCLUSION: Compared with R0, R1cis significantly deteriorated overall survival in the whole resection subset of patients with perihilar cholangiocarcinoma. However, the prognostic impact of R1cis was milder than that of R1inv.