(A) C57BL/6 mice were treated with quercetin (100 mg/kg/day, p.o.) four days before the i.p. administration of DOX (20 mg/kg). Livers were removed five days after DOX treatment, and the sections were stained with hematoxylin and eosin (H&E; magnification 200×). (B) SMMC7721 cell-derived tumors were developed in nude mice and treated with saline, quercetin, DOX, and DOX + quercetin. At the end of three weeks, livers were collected and stained with H&E. (C) A model of the effect of quercetion on DOX in liver cells. In this model, quercetin increases DOX-induced p53 expression in liver cancer cells and reduces Bcl-xl expression, thereby increasing caspase −3/−9 activity and potentiating DOX-induced cell death in liver cancer cells. Quercetin decreases DOX-induced oxidative stress and increases cell survival in normal liver cells.