FIGURE 2.

The Mechanisms of tumor drug resistance. Tumor heterogeneity is usually caused by chromosomal instability, mutations and epigenetics changes. Cancer stem cells can resist drugs by increasing the expression of ABC, dormant by arresting cell cycle, improving repair ability, and creating a hypoxic niche; The components of TME, including cells and cytokines, can cause tumor cells to resist drugs. Last but not least, tumors can resist drugs by reducing absorption, changing activity, affecting metabolism and increasing excretion. ABC, adenosine-triphosphate binding cassette; CSCs, cancer stem cells; TME, tumor micro environment.