In vivo effects of CTet on the growth of human MCF-7 breast cancer cell-derived tumors from xenografts in athymic mice. Athymic female mice were inoculated with MCF-7 cells and then intraperitoneally treated with CTet (5 mg/kg) or vehicle (γ-cyclodextrin solution) for 2 weeks, as described in Materials and methods. The percentage of residual tumor mass has been calculated with respect to time 0, which corresponds to the start of treatment. Positive control (CTR) refers to four mice bearing the tumor and not treated, CTR + vehicle refers to four mice bearing the tumor and receiving the vehicle, and CTR + CTet refers to five mice bearing the tumor and receiving CTet. The results are presented as mean ± standard deviation of the number of mice indicated above. The asterisk indicates statistically significant value with respect to CTR and CTR + vehicle (Mann-Whitney test; P < 0.05). CTet, indole-3-carbinol cyclic tetrameric derivative.