Experimental protocols for prevention and treatment models of breast cancer, and sensitivity of 4T1 cells to tamoxifen. A: Experimental protocols. In the prevention model, mice were placed on the control diet or the Fe-Lf diet, and 4T1 tumor cells were injected into the mammary fat pad 14 days later. Tamoxifen or PBS was administered i.p. on the day the mice were placed on their diets, and on alternate days thereafter. Six mice per group (n = 18) were randomly killed at the indicated time points. In the treatment model, the mice were placed on the diets and 4T1 cells were injected into the mammary fat pad 14 days later. Tamoxifen or PBS was administered 14 days after injection of tumor cells, and on alternate days thereafter. Each group had 6 mice, which were killed at the completion of the experiment. B: Tamoxifen has chemotherapeutic effects against 4T1 cells. 4T1 cells were incubated with increasing concentrations of tamoxifen, and their viability assessed 72 h later by the MTT assay. The cell viability index (% viability) was plotted versus the concentration of tamoxifen.