Objective: Tumor associated macrophages (TAMs) promoted pancreatic ductal adenocarcinoma (PDAC) initiation and progression. In this study we aimed to evaluate CD10 expression by monocytes/macrophages and its clinical significance in PDAC. Methods: Human CD14(+) peripheral blood monocytes were isolated and cultured for 6-7 days to differentiate into macrophages in vitro. Monocytic THP-1 cells were cultured and treated with 100 ng/ml phorbol 12-myristate 13-acetate (PMA) for 72 h to induce macrophage differentiation. Reverse transcription-quantitative PCR, immunohistochemistry, immunofluorescence, multiplex immunohistochemical staining and flow cytometry were performed to detect CD10 expression. In addition, the correlations between CD10 expression and immune cells infiltration were investigated through TIMER or GEPIA. Finally, Kaplan-Meier plotter and GEPIA databases were adopted to evaluate the influence of CD10 on clinical prognosis. Results: Our results indicated that CD10 was expressed by a subset of human monocytes and many more cells expressed CD10 after differentiation into macrophages in vitro (13.19% vs. 41.39%; P < 0.0001). As for PDAC tissues, CD10 was correlated with immune cells infiltration and was expressed by a subset of TAMs. For THP-1 cells, PMA could induce CD10 expression through the MAPK pathway. The Kaplan-Meier plotter results suggested that CD10 expression had an impact on the prognosis of PDAC. Conclusions: In this study we demonstrated that CD10 was expressed by human primary monocytes, human monocyte-derived macrophages and TAMs, and was correlated with poor prognosis in PDAC, suggesting CD10 to be a potential therapeutic target in PDAC. (C) 2020 The Author(s). Published by Elsevier Inc.