To more precisely determine cell-based LIMK inhibitor activity, MCF7 breast cancer cells were treated with 2 μg/mL doxorubicin, which strongly increases cofilin phosphorylation through increased p53-mediated transcription of LIMK2 and RhoC genes [12] to increase the dynamic range and signal-to-noise ratio of the assay, and varying concentrations of LIMK inhibitors for 18 hr, then cells were fixed and stained for immunofluorescence determination of phosphorylated cofilin intensity. This evidence concerns the gene CFL1 and breast cancer.