SERPINB2 (serpin family B member 2), also known as plasminogen activator inhibitor type 2 (PAI-2), is a serine protease inhibitor with multifaceted roles in inflammation, immunity, and cancer biology. Originally characterized as an inhibitor of urokinase-type plasminogen activator 1, SERPINB2's physiological significance extends far beyond this canonical function. The protein is substantially upregulated under inflammatory conditions and is abundantly expressed by activated macrophages and hematopoietic cells 1. Mechanistically, SERPINB2 expression is regulated by multiple stimuli including NF-κB signaling 2, IL-13/STAT6 pathways 3, and estrogen receptor signaling 4. In tumor-associated macrophages, SERPINB2 is regulated by STAT1 and functions as a tumor-suppressive secretory factor that inhibits cancer stemness 5. Clinically, SERPINB2 demonstrates dual roles: it functions as a tumor suppressor in esophageal and breast cancers by suppressing cell migration and promoting apoptosis 24, while in chr18 rhinosinusitis with nasal polyps, elevated SERPINB2 contributes to type-2 inflammation via STAT6-dependent 15LO1 induction 3. Additionally, SERPINB2 modulates adaptive immune responses, with knockout mice showing enhanced Th1 responses 1. Its upregulation during mesenchymal stem cell differentiation suggests roles in lineage commitment 6.