Effects of anticancer drugs on the survival of 3D multicellular tumor spheroids. Stromal cells and the breast cancer cells were co‐cultured to form tumor spheroids for 48 h, and anticancer drugs were treated to the spheroids for an additional 48 h. Disposition of (a) doxorubicin, (b) epirubicin, and (c) topotecan penetrated into the tumor spheroids. Quantifications of fluorescence intensity for anticancer drugs were indicated in the graph. ***p < 0.001, ****p < 0.0001 (one‐way ANOVA), n = 3 per group. Scale bars, 200 μm (a) and 100 μm (b) and (c). (d) Efficacy of anticancer drugs in the tumor spheroids. *p < 0.05, **p < 0.01, ****p < 0.0001 (one‐way ANOVA), n = 3 per group. (e) Relative fold changes of necrotic cells in tumor spheroids by anticancer drug treatment. Necrotic cells in the tumor spheroids before drug treatment are presented as 1. n = 3 per group. All data are presented as mean ± SEM. 3D, three dimension; ANOVA, analysis of variance; NS, not significant; SEM, standard error of the mean; TIMP‐1, tissue inhibitor of metalloproteinases‐1