In spite of these findings, the development of ABCG2 inhibitors is being expedited, because ABCG2 provides multidrug resistance for tumor cells by active drug efflux, thus the bioavailability of anticancer drugs can be improved by co-administration with ABCG2 inhibitors (Breedveld et al., 2006; Wu et al., 2008). The gene discussed is ABCG2; the disease is neoplasm.