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The benefit and indicationof adjuvant RT has is unclear. The goal of this study is to identify the role of adjuvant radiation therapy (RT) in non-hilar extrahepatic bile duct cancer (NH-EHBDC) patients treated with radical surgery by identifying subgroups that benefit from adjuvant RT and to suggest a potential indication for adjuvant RT.

We retrospectively reviewed NH-EHBDC patients who underwent radical surgery with or without adjuvant treatment from October 2004 to June 2018 at our institution. Patients treated with any neoadjuvant treatment, incomplete RT, histology other than adenocarcinoma, or history of cancer without 5 years of no evidence of disease period before the diagnosis of NH-EHBDC were excluded. Finally, 332 patients were included in our study. For pT3 stage, positive node, and R1 resected patients, adjuvant concurrent chemoradiation was recommended. Univariate and multivariate analyses were conducted to identify prognostic factors for locoregional recurrence-free survival (LRRFS), distant metastasis-free survival (DMFS), disease-free survival (DFS), and overall survival (OS). High-risk patients for locoregional recurrence were analyzed to identify the role of adjuvant RT.

Overall, 131 (39.5%), 25 (7.5%), 7 (2.1%), 167 (50.3%), and 2 (0.6%) patients received no adjuvant treatment, adjuvant chemotherapy, adjuvant RT, adjuvant concurrent chemoradiation ± maintenance chemotherapy, and sequential chemoradiation, respectively. Median RT dose was 50.4Gy (range, 40-59.4Gy). At a median follow-up of 32.2 months (range, 1.6-178.0 months), 3-year LRRFS, DMFS, DFS, and OS were 73.8%, 57.4%, 49.1%, and 64.6%, respectively. In multivariate analysis, adjuvant RT ≥ 50Gy (vs. no RT, HR 0.48, P=0.002), preoperative CA19-9 > 37U/mL (HR 1.79, P=0.013), bile duct resection or hilar resection (vs. pancreaticoduodenectomy or pylorus-preserving pancreaticoduodenectomy, HR 2.25, P=0.021) nodal involvement (HR 1.65, P=0.036), and venous invasion (HR 1.77, P=0.024) were identified as independent prognostic factors for LRRFS. For pT3 stage (81.6% vs 63.7%, P=0.030), node positive (78.9% vs 52.5%, P=0.002), and R1 resected patients (87.5% vs 0.0%, P=0.017), adjuvant RT ≥ 50Gy significantly improved 3-year LRRFS. However, in patients with preoperative CA19-9 > 37U/mL (77.9% vs 59.6%, P=0.100), bile duct resection or hilar resection (68.7% vs 43.9%, P=0.100), venous invasion (67.9% vs 41.2%, P=0.082), the benefit of adjuvant RT was not statistically significant. In node positive patients and R1 resected patients, adjuvant RT ≥ 50Gy significantly improved DFS and OS, respectively. Impact of chemotherapy was not observed over various treatment end-points.

In patients with NH-EHBDC, the use of adjuvant RT ≥ 50 Gy significantly improved LRRFS. For patients who are at high risk of locoregional recurrence, especially for patients with nodal involvement or R1 resected patients, adjuvant RT should be considered in order to achieve improved survival.