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 µ µ µ µg/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 1000 µ µ µ µg/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-α α α α, using ELISA. (1) NE degrades a broad spectrum of extracellular matrix and cell surface proteins, such as elastin, interstitial collagens, proteoglycans, fibronectin, laminin, and type IV collagens.(2-5) Under normal physiological conditions, the proteolytic activity of elastase released by recruited neutrophils is strictly regulated by antiproteases, such as alpha-1-protease inhibitor and secretary leukoprotease inhibitor. However, under conditions of physiological disturbance, such as the presence of neoplasms, surgical stress, or inflammation, the balance between elastase and antiprotease is disrupted, and the predominant elastolytic activity causes the destruction of THE extracellular matrix. NE also cleaves pro-TGF-α on the surface of human airway epithelial cells through its proteolytic activity and releases mature, soluble TGF-α on human airway epithelial cells.(6) Release of TGF-α activates the EGFR signaling cascade, (6) resulting in mucinous secretion in the peripheral airways that might cause severe respiratory complications after major surgical stress or severe inflammatory response.Recently, a specific synthetic NE inhibitor, sivelestat, has been developed and used clinically in Japan for the treatment of various inflammatory diseases. The anti-inflammatory effects of sivelestat are effective for the alleviation of surgical stress, and can reduce morbidity and organ dysfunction, including acute respiratory distress syndrome. As mentioned above, sivelestat inhibits the NE-induced release of TGF-α from the cell membrane.As we have previously demonstrated, gastric and esophageal carcinoma cells have been found to have multi-autocrine loops for the development of growth and metastatic potential (7)(8)(9)(10)(11) in laboratory studies. In the clinical setting, relapses or rapid recurrences are often observed after extensive resection of gastric and esophageal tumors, suggesting that strong inflammatory responses are present, including the release of NE, which might cause the rapid spread of cancer cells. These facts prompted us to exam...