The quantification of Ki-67 proliferation index (the percentage of Ki-67-positive cells to tumor cells) revealed that the average percentage of Ki-67-positive cells in 4T1 alone tumors was 19.21%, while there was a significantly higher percentage of proliferation cells in 4T1 + mBM-MSCs tumors (40.6%; P <0.05) (Figure 5c). The gene discussed is MKI67; the disease is neoplasm.