TSPAN1 belongs to the large family of tetraspanins, so named because they contain 4 transmembrane domains. TSPAN1 is expressed in colon, endometrium, pancreas, normal and neoplastic prostate, and pregnant uterus. Tetraspanins are frequently expressed at the cell surface in association with each other and with other molecules, such as integrins, and they function to regulate cell adhesion, migration, proliferation, and differentiation. RNAi-mediated downregulation of TSPAN1 expression significantly inhibits the proliferation and invasion of colon cancer cells in vitro. This finding suggests that TSPAN1 plays an important role in colon cancer progression.