The ADAMs (A disintegrin and metalloproteinase) are a family of cell-surface membrane glycoproteins, whose multidomain structure enables diverse roles in a wide range of cellular processes. Accumulating evidence associates an increased expression of individual ADAM family members with various types of cancer, and we investigated the possible involvement of ADAM9, 12 and 15 in the pathogenesis of gastric cancer (GC). Using immunohistochemistry and quantitative RT-PCR, we examined the transcription and expression pattern of ADAM9, 12, and 15 in GCs and the corresponding non-tumor tissue, and in GC cell lines (AGS, MKN45, MKN28, NCI-N87, KATOIII). All three ADAMs were found to be significantly upregulated in GC compared to non-neoplastic foveolar epithelium, with ADAM12 expression being higher in intestinal- than in diffuse-type tumors. In vitro proliferation assays were used to evaluate the effects of ADAM-specific antibodies on the growth of GC cell lines. The administration of anti-ADAM9 and anti-ADAM15 antibodies inhibited cell growth, whereas anti-ADAM12 enhanced the proliferation of the GC cell lines. ADAM9, 12 and 15 are implicated in the malignant growth of GC cells, perhaps via the interaction with adhesion molecules, or the proteolytic 'shedding' of signaling molecules and the consequent transactivation of their receptors, such as the epithelial growth factor receptor and its ligands. The resultant modulation of the tumor-host interface may contribute to the pathogenesis, development or progression of gastric cancer.