CD9 and cancer: It has been reported that many tetraspanins such as Tspan1 (NET-1), Tspan8 (CO-029), Tspan13 (NET-6), Tspan24 (CD151), Tspan27 (CD82), Tspan28 (CD81), Tspan29 (CD9) and Tspan30 (CD63) were deregulated in various types of human cancers, implying that these tetraspanins may be involved in tumourigenesis and/or tumour progression [11–17].