MDM2 and neoplasm: For example, USP15 can act as a tumor promoter in estrogen receptor-positive breast cancer by deubiquitinating and thereby stabilizing the estrogen receptor51, by stabilizing TGF-β receptor 1 (TGFβR1) in glioblastoma31, or by deubiquitinating and stabilizing MDM2, leading to p53 inactivation28.