ABCG2 and neoplasm: Furthermore, chronic CerS4 overexpression upregulated ABC transporters, such as ABCC1, ABCC2, ABCC4, ABCB1, and ABCG2. A major mechanism underlying MDR development is thought to be the overexpression of ABC transporters, which leads to the efflux of anticancer agents from tumor cells [42, 43].