MDA-MB-231 25PACR cells maintained resistance to paclitaxel after prolonged culture without exposure to taxane. MDA-MB-231 25PACR cells were separated into two groups: one maintained and passaged, as normal in the presence of paclitaxel (white bar), the other was maintained and passaged in the absence of drug (grey bar)for a period of six months. The native cells are represented by the black bar. Cells were incubated with varying concentrations of paclitaxel and cell viability determined by CCK-8 assay. The X axis shows the increasing paclitaxel concentration measured in nM. The Y axis represents the percentage of cells with untreated cells being used as a baseline of 100%.