Background Extrahepatic cholangiocarcinoma is very difficult to diagnose at an early stage, and has a poor prognosis. Novel markers for diagnosis and optimal treatment selection are needed. However, there has been very limited data on the proteome profile of extrahepatic cholangiocarcinoma. This study was designed to unravel the proteome profile of this disease and to identify overexpressed proteins using mass spectrometry-based proteomic approaches. Methods We analyzed a discovery set of formalin-fixed paraffin-embedded tissues of 14 extrahepatic cholangiocarcinomas using shotgun mass spectrometry, and compared proteome profiles with those of seven controls. Then, selected candidates were verified by quantitative analysis using scheduled selected reaction monitoring-based mass spectrometry. Furthermore, immunohistochemical staining used a validation set of 165 cases. Results In total, 1,992 proteins were identified and 136 proteins were overexpressed. Verification of 58 selected proteins by quantitative analysis revealed 11 overexpressed proteins. Immunohistochemical validation for 10 proteins showed positive rates of S100P (84%), CEAM5 (75%), MUC5A (62%), OLFM4 (60%), OAT (42%), CAD17 (41%), FABPL (38%), AOFA (30%), K1C20 (25%) and CPSM (22%) in extrahepatic cholangiocarcinomas, which were rarely positive in controls. Conclusions We identified 10 proteins associated with extrahepatic cholangiocarcinoma using proteomic approaches. These proteins are potential targets for future diagnostic biomarkers and therapy.
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