BACKGROUNDIntrahepatic cholangiocarcinoma (ICC) is the second most common primary liver cancer in humans after hepatocellular carcinoma and a rare epithelial malignancy that results in a poor prognosis. According to the Liver Cancer Study Group of Japan classification, ICC can be divided into three types: Mass-forming (MF) type, periductal-infiltrating (PI) type, and intraductal-growth type. The MF type is the most common, accounting for 57.1-83.6% of ICCs. Nevertheless, little is known about the epidemiology and treatment of MF ICC.AIMTo examine the prognostic factors for patients with MF ICC.METHODSWe carried out a retrospective analysis of consecutive patients with MF ICC treated at the Faculty of Hepato-Pancreato-Biliary Surgery of Chinese PLA General Hospital between January 2008 and December 2018. According to the treatment received, the patients were divided into either a resection group or an exploration group.RESULTSThe pooled 1-, 3-, and 5-year survival rates in the 68 patients with MF ICC were 66.5%, 36.3%, and 9.3%, respectively. Univariate analysis revealed that surgical resection (P < 0.001), nodal metastasis (P < 0.001), tumor location (P = 0.039), vascular invasion (P < 0.001), ascites (P < 0.001), and differentiation (P = 0.009) were significantly associated with the prognosis and survival of MF ICC. Multivariate analysis revealed that ascites (hazard ratio [HR] = 5.6, 95% confidence interval [CI]: 1.6-18.9, P = 0.006) and vascular invasion (HR = 2.5, 95%CI: 1.0-6.1, P = 0.045) were independent risk factors for MF ICC. The pooled 1-, 3-, and 5-year survival rates in the 19 patients of the exploration group were 5.3%, 5.3%, and 0, respectively. Among the 49 patients who underwent surgical resection, the pooled 1-, 3-, and 5-year survival rates were 93.5%, 49.7%, and 14.4%, respectively. Univariate and multivariate analyses revealed that vascular invasion (HR = 3.1, 95%CI: 1.2-8.5, P = 0.024) and nodal metastasis (HR = 3.2, 95%CI: 1.4-7.6, P = 0.008) were independent prognostic risk factors for surgical resection patients.CONCLUSIONThe prognosis of MF ICC patients is dismal, especially those with ascites or vascular invasion. Surgical resection is a key factor in improving overall survival in patients with MF ICC, and vascular invasion and lymph node metastasis affect the efficacy of surgical resection.