USP7 and hepatocellular carcinoma: USP7 promotes the growth of non-small cell lung cancer cells by stabilizing Ki-67 protein, while metformin can inhibit the proliferation of esophageal cancer by upregulating USP7, suggesting that USP7 plays different roles in different types of tumors [50-52], USP4 and USP15 can stabilize TGF-β receptors and increase TGF-β-mediated EMT, leading to metastasis of hepatocellular carcinoma and glioblastoma [53-55].