ABCG2 and neoplasm: Many studies have elucidated the additional roles of ABC transporters in cancer initiation and progression [8]: for example, (1) ABCB1 has been reported to inhibit the apoptotic cascade in both normal and cancer cells; (2) knockdown of ABCB1 by small interfering RNA suppressed cancer cell proliferation and tumor expansion in a mouse xenograft model; (3) ABCB1 has also been reported to play a role in cell proliferation and delivering of protumorigenic platelet activating factor to its receptor.