Lastly, we have a solid foundation for genetic, epigenetic, and transcriptional mechanisms of ABCB1/P-gp upregulation in cancer, having identified many of the key players and processes involved; however, many of the proposed pathways have not established whether regulation is direct or indirect, and moving forward we need to characterize exactly how ABCB1/P-gp is becoming overexpressed. Here, PGP is linked to cancer.