TGFB1 and neoplasm: However, when USP15 is overexpressed, the body perceives TGFβ levels to be underexpressed and may tip the balance towards deubiquitination [25], leading to overexpression of TGFβ and thus promoting tumor proliferation and migration [30, 31], The only commercially available small molecule compound with significant inhibitory effects on USP15 is the broad-spectrum ubiquitination inhibitor PR-619, which inevitably inhibits other deubiquitination enzymes while inhibiting USP15, causing several unknown side effects [32, 33].