As shown in Figure 1, rutaecarpine significantly sensitized ABCB1-overexpressing cancer cells MCF-7/ADR (Figure 1A–C) and A549/Taxol (Figure 1E–G) to ABCB1 transport substrates, compared with the resistance cells without rutaecarpine, and this sensitization occurred in a dose-dependent manner. This evidence concerns the gene ABCB1 and cancer.