Abstract： Objective:To investigate the expression of glypican1 (GPC1) in pancreatic ductal adenocarcinoma (PDAC) and its relationship with the prognosis of patients with PDAC.Methods:From January 2015 to December 2018, 125 PDAC tumor specimens and corresponding para-carcinoma normal pancreatic tissue were collected from the Department of Pathology of Peking University Third Hospital. The expression of GPC1 protein was detected by the immunohistochemical Envision two-step method in all specimens. The specimens were divided into high and low GPC1 expression groups according to immunohistochemical scores, and the correlation between GPC1 protein expression and clinicopathological features and overall survival time was analyzed.Results:The positive expression rate of GPC1 protein was 0 score in 30.4% of PDAC tissues, 1 score in 15.2%, 2 score in 18.4% and 3 score in 36.0%, respectively, and high expression rate (2+ 3) was 54.4%. GPC1 protein was negatively expressed in para-carcinoma pancreatic tissues. The positive expression rate of GPC1 protein in PDAC tissue was significantly higher than that in para-carcinoma pancreatic tissue, and the difference was statistically significant ( P=0.000). The high expression of GPC1 protein was significantly correlated with tumor location and T stage ( P<0.05), but not with gender, age, history of diabetes and pancreatitis, preoperative blood CA19-9 level, postoperative surgical margin, tumor differentiation, lymph node metastasis, nerve invasion and vascular invasion (all P values >0.05). Univariate Cox proportional hazards analysis showed that GPC1 expression was associated with postoperative overall survival time in PDAC patients ( P<0.001). Multivariate Cox proportional hazards analysis showed that GPC1 protein expression level was an independent prognostic factor affecting overall survival time in PDAC patients ( P<0.001). The median survival time of PDAC patients with high GPC1 expression was significantly lower than that of PDAC patients with low GPC1 expression (11.00 months vs 18.00 months), and the difference was statistically significant ( P<0.01). Conclusions:GPC1 protein was abnormally high expressed in PDAC tumor tissue, and the high expression of GPC1 protein was positively correlated with tumor stage and negatively correlated with the overall survival time of patients. High expression of GPC1 was an independent risk factor for poor prognosis in PDAC patients.