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Differential diagnosis of intrahepatic cholangiocarcinoma (iCCA) from its histologic mimickers, especially metastatic adenocarcinomas of gastric and pancreatic origin, is a great challenge for pathologists. In this study, through bioinformatics analysis of data from The Cancer Genome Atlas and Gene Expression Omnibus, we identified C-reactive protein (CRP) as a candidate marker to differentiate iCCA from other adenocarcinomas and validated its diagnostic performance by immunohistochemistry in a large cohort of clinical samples including 103 iCCAs, 384 other adenocarcinomas, and 34 liver metastases of various origins. The sensitivity and specificity of CRP expression in the diagnosis of iCCA were 75.7% and 91.1% when using tissue microarrays and 93.3% and 88.2% when using whole tissue sections, respectively. We also compared the diagnostic performance of CRP with N-cadherin, a previously reported marker for iCCA. The sensitivity and specificity of N-cadherin were 54.4% and 92.2% when using tissue microarrays and 80.0% and 88.2% when using whole tissue sections, respectively. The sensitivity of CRP was higher than that of N-cadherin, whereas their specificity was similar. CRP expression was associated with mass-forming gross type (P<0.001), absence of perineural invasion (P=0.002), and N-cadherin expression (P<0.001). CRP expression was also associated with better overall survival (P=0.002) and longer recurrence-free time (P=0.032) after surgery. Our study suggests that CRP is a promising immunohistochemical marker to differentiate iCCA from other adenocarcinomas. Compared with N-cadherin, CRP showed higher sensitivity and similar specificity. CRP expression was associated with better prognosis in iCCA.