Normal myoepithelial cells suppress invasion and dissemination of C3-1-T tumor cells. (A) Tumor cells (mT⁺; red) were isolated from C3-1-Tag;mT/mG mice and normal myoepithelial cells (GFP⁺; green) were isolated from K14::Actin-GFP mice via FACS. Tumor cells were aggregated with normal myoepithelial cells at different ratios to form clusters, and aggregated clusters were cultured in 3D collagen I. (B–C′′′) The clusters were divided into four groups and monitored for dissemination. The number of disseminated cells per cluster decreased with an increasing number of normal myoepithelial cells. Arrowheads indicate disseminated cells. (D and D′) Myoepithelial cells appeared to contain invasion past the myoepithelial layer and reestablish a continuous myoepithelial layer. (E and E′) Myoepithelial cells were also observed to extend into the collagen and capture disseminated tumor cells. (F) Tumor cell restraint, recapture, and dissemination quantified from real-time confocal videos across multiple replicates. n, total number of organoids; r, number of biological replicates. Data were analyzed by two-tailed nonparametric Kruskal–Wallis multiple comparisons test: ****, P < 0.0001. Data are presented as box plots, with error bars representing the 5th to 95th percentile. Myoepithelial cells in time-lapse videos are pseudocolored in green.