Aim: To investigate the role of CCL5 secreted by tumor associated macrophages (TAMs) in gastric cancer, and to explore how CCL5/CCR5 axis modulates phenotypes of gastric cancer cells. Methods: Expression of CCL5 and TAM surface marker CD68 in gastric cancer tissues was examined using SP immunohistochemistry. Serum CCL5 levels of patients were assessed using ELISA. Cross-analyses of CCL5 and CD68 expression with clinicopathological data were done. Correlation between CCL5 and CD68 in gastric cancer tissues was also studied. In vitro functional characterization of CCL5 in gastric cancer was done in co-culture of AGS and THP-1 derived macrophages using MTS assay, plate clone formation assay, and transwell experiment. Expression of chemokines and its receptors were detected by RT-PCR, while Stat3 phosphorylation and downstream target proteins were studied using western blot. Results: CCL5 and CD68 were both highly expressed in tissues gastric cancer, of which the expressions were positively correlated with each other, and of clinical importance, were associated with the depth of invasion, lymph node metastasis, TNM staging and tumor differentiation. Serum CCL5 was also elevated in patients with gastric cancer comparing to healthy volunteers. Co-culture of AGS cells with THP-1 derived macrophages increased cell proliferation, clone forming ability as well as migration of AGS cells. Migration of AGS cells across transwell membrane was also enhanced by increasing exogenous CCL5. Meanwhile, mRNA expression of CCL5, MMP2, MMP9, and CCR5 was also highly expressed in the cells. Stat3 signaling as reflected by its phosphorylation was also increased in AGS cells upon co-culture with THP-1 derived macrophages. Conclusion: CCL5 secreted by TAMs may promote the proliferation, invasion and metastasis of gastric cancer cells, in which Stat3 signaling pathway is likely to play an important role. The correlation of CCL5 with clinicopathological parameters suggested CCL5 holds promise as important molecular marker of gastric cancer staging and disease progression. (C) 2015 Elsevier Masson SAS. All rights reserved.