PLAU and neoplasm: To date, only a few secretory serpins have been shown to indirectly inhibit matrix metalloproteinase (MMP) activity by directly inhibiting the serine protease activity of urokinase-type plasminogen activator (uPA) secreted by tumor cells, thereby controlling the migration and invasion of tumor cells [1, 2], such as pigment epithelium-derived factors (PEDFs), plasminogen activator inhibitor 1 (PAI-1), protease Nexin-1 (PN-1), and α1-antichymotrypsin (α1-ACT); thus, it is necessary to discover and introduce new inhibitory serpins with better therapeutic effects as tumor-targeted drugs [3].