There are 33 human tetraspanin proteins,emerging as key players in malignancy,the immune system,fertilization,cellular signaling,adhesion,morphology,motility,proliferation,and tumor invasion.CD9,a member of the tetraspanin family,associates with and influences a variety of cell-surface molecules.Through these interactions,CD9 modifies multiple cellular events,including adhesion,migration,proliferation,and survival.CD9 is therefore considered to play a role in several stages during cancer development.Reduced CD9 expression is generally related to venous vessel invasion and metastasis as well as poor prognosis.We found that treatment of mice bearing human gastric cancer cells with anti-CD9 antibody successfully inhibited tumor progression via antiproliferative,proapoptotic,and antiangiogenic effects,strongly indicating that CD9 is a possible therapeutic target in patients with gastric cancer.Here,we describe the possibility of CD9 manipulation as a novel therapeutic strategy in gastric cancer,which still shows poor prognosis. There are 33 human tetraspanin proteins, emerging as key players in malignancy, the immune system, fertilization, cellular signaling, adhesion, morphology, motility, proliferation, and tumor invasion. CD9, a member of the tetraspanin family, associates with and influences a variety CD9 modifies multiple cellular events, including adhesion, migration, proliferation, and survival. CD9 is therefore considered to play a role in several stages during cancer development. Reduced CD9 expression is generally related to venous vessels invasion and metastasis as well as poor prognosis. We found that treatment of mice bearing human gastric cancer cells with anti-CD9 antibody successfully was tumor growth via antiproliferative, proapoptotic, and antiangiogenic effects, strongly indicating that CD9 is a possible therapeutic target in patients with gastric cancer. Here, we describe the possibility of CD9 manipulation as a novel therapeutic strategy in gastric c ancer, which still shows poor prognosis