Neutrophil elastase is a neutral serine proteinase produced by polymorphonuclear leukocytes and monocytes/macrophages, especially under surgical stress. In the present study, we investigated whether NE promotes cell growth by activation of EGFR to elucidate whether surgical stress induces tumor proliferation and progression. Furthermore, we examined the antitumor effect of a specific NE inhibitor, sivelestat. Cell growth assays were carried out in vitro and in vivo using TMK-1 gastric cancer cells. TMK-1 cell growth was stimulated to 118% of that of the control cells after 48 h stimulation with 1 microg/mL NE according to an MTT assay. Sivelestat inhibited cell growth to 23.4 and 58.0% of control values at concentrations of 100 and 1,000 microg/mL, respectively. NE rapidly phosphorylated EGFR in only 5 min and triggered the ERK1/2-mitogenic signaling pathway in TMK-1. It was further demonstrated that NE-induced EGFR phosphorylation was transactivated through TGF-alpha, using ELISA. NE increased the cleavage of TGF-alpha from the cell surface 30-fold compared with the cells without treatment. Interestingly, sivelestat significantly reduced NE-induced EGFR phosphorylation and ERK1/2 activation and completely blocked the release of TGF-alpha from the TMK-1 cell surface. In a xenograft study, the addition of ventrotomy as a surgical stress promoted tumor growth. Sivelestat significantly suppressed the tumor growth induced by surgical stress. These results indicate that sivelestat suppresses the growth of gastric cancer cells by inhibiting the release of TGF-alpha stimulated by NE, which often occurs after surgical stresses.