3,6-Dihydroxyflavone significantly inhibited the growth of MDA-MB-231 cells in athymic mice. The weight of the mice and the tumor volume were recorded every 4 days until animal sacrifice at day 28. (A) Tumor volume in each group. (B) Tumor weight at the end of the 28-day treatment. (C) Photograph of tumors at the end of the treatment. Data presented as mean ± standard deviation (n = 6). **P < 0.01 compared with control.