Depending on the compound molecular structure, the MDR reversion mechanism can be dependent on direct inhibition of the ABC transporter, suppression of the transporter genes, and/or be accompanied by anti-tumor activity exerted on target pathways such as PI3K (phosphoinositide 3-kinase) or NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells) [87,88]. The gene discussed is ABCG2; the disease is neoplasm.