SERPINB12 is an intracellular serine protease inhibitor (serpin) predominantly expressed in epithelial tissues throughout the body 1. Its primary function is to inhibit trypsin-like serine proteinases, including trypsin and plasmin, but not thrombin, coagulation factor Xa, or urokinase-type plasminogen activator 2. SERPINB12 additionally acts as a slow-binding inhibitor of granzyme A and hepsin 3. Beyond protease inhibition, SERPINB12 plays a regulatory role in intestinal epithelial cell differentiation through interaction with Schlafen 12 (SLFN12) and deubiquitylases (UCHL5 and USP14), promoting sucrase-isomaltase expression and CDX2 stabilization—a pathway potentially targetable in mucosal atrophy and short gut syndrome 4. Clinically, SERPINB12 is dysregulated in multiple disease contexts: it is upregulated in smoking-associated non-small cell lung cancer (NSCLC), where it promotes proliferation and metastasis via Wnt/β-catenin signaling and correlates with poor prognosis 5; it is estrogen-regulated and upregulated in epithelial ovarian carcinomas 6; and it is downregulated in extracellular vesicles from substance use disorder patients, correlating with neuroinflammatory changes 7. These findings establish SERPINB12 as both a potential biomarker and therapeutic target across multiple malignancies and neurological conditions.