AbstractBackground & AimsAs most staging systems for intrahepatic cholangiocarcinoma (iCCA) are based on pathological results, preoperative prognostic prediction is limited. This study aimed to develop and validate a prognostic model for the overall survival of patients with mass‐forming iCCA (MF‐iCCA) using preoperative magnetic resonance imaging (MRI) and clinical findings.MethodsWe enrolled a total of 316 patients who underwent preoperative MRI and surgical resection for treatment‐naive MF‐iCCA from six institutions, between January 2009 and December 2015. The subjects were randomly assigned to a training set (n = 208) or validation set (n = 108). The MRIs were independently reviewed by three abdominal radiologists. Using MRI and clinical findings, an MRI prognostic score was established. We compared the discrimination performance of MRI prognostic scores with those of conventional pathological staging systems.ResultsWe developed an MRI prognostic score consisting of serum CA19‐9 and three MRI findings (tumour multiplicity, lymph node metastasis and bile duct invasion). The MRI prognostic score demonstrated good discrimination performance in both the training set (C‐index, 0.738; 95% confidence interval [CI], 0.698–0.780) and validation set (C‐index, 0.605; 95% CI, 0.526–0.680). In the validation set, MRI prognostic score showed no significant difference with AJCC 8th TNM stage, MEGNA score and Nathan’s stage.ConclusionsOur MRI prognostic score for overall survival of MF‐iCCA showed comparable discriminatory performance with pathological staging systems and might be used to determine an optimal treatment strategy.