Evaluation of cell proliferation in nude mice by H&E staining and IHC revealed that Ki-67-positive cells in tumors of the oe-USP21 group were notably more than those in the control group, and the tumor grade was positively correlated with the number of Ki-67-positive cells as well as the content of USP21 (Figure 6E). The gene discussed is MKI67; the disease is neoplasm.