Abstract
Pancreatic ductal adenocarcinoma (PDAC) accounts for 85–90% of all pancreatic tumours. The median survival of all PDAC patients is less than 6 months, and the recent 5-year-survival rate is approximately 8%. One of the most crucial reasons for the poor prognosis is the lack of early diagnostic markers for PDAC. To overcome this and improve the outcomes of patients with PDAC, there is an urgent need to identify highly sensitive and specific markers for early detection. The widely used serum-circulating markers for PDAC, carbohydrate tumour–associated antigen 19-9 (CA19-9) and carcinoembryonic antigen (CEA), are not sufficiently accurate to be used as early diagnostic markers. The interplay between cancer cells and stromal components, including soluble mediators released from cancer cells, contributes to the progression of PDAC. Here, we set out to identify key secreted proteins involved in PDAC progression. In the present study, we performed secretome analyses of culture media of mouse pancreatic intraepithelial neoplasia (PanIN) and PDAC cells using Stable Isotope Labeling by Amino acid in Cell culture (SILAC) with click chemistry and liquid chromatography-mass spectrometry (LC-MS/MS). Furthermore, we compared the serum levels of candidate proteins to evaluate the ability to discriminate between PDAC and healthy controls. The sera levels of Protein X were significantly higher in the preoperative PDAC patients than those in the postoperative ones (p