CYP4B1 is a cytochrome P450 monooxygenase primarily expressed in extrahepatic tissues, particularly the lung, rather than liver 1. The enzyme catalyzes NADPH-dependent oxidation of diverse substrates including xenobiotics, fatty acids, and fatty alcohols through omega-hydroxylation 2. CYP4B1 bioactivates protoxic xenobiotics such as 4-ipomeanol, valproic acid, and aromatic amines, leading to tissue-specific toxicities 2. Notably, human CYP4B1 lacks catalytic activity due to a proline-427-to-serine substitution unique among P450 enzymes, contrasting with catalytically active rabbit orthologs 1. Despite functional inactivity in humans, CYP4B1 expression associates with various cancers, including lung adenocarcinoma and gastric cancer 34. The rs4646491 polymorphism correlates with increased gastric cancer susceptibility in Chinese populations 4. CYP4B1 expression is reduced 2.3-2.4 fold in lung tumors compared to normal lung tissue 5. Therapeutically, reengineered CYP4B1 combined with 4-ipomeanol prodrug shows promise for suicide gene therapy in cancer treatment 3. Genetic polymorphisms vary significantly across populations, with CYP4B1(*1) and CYP4B1(*2) allele frequencies differing substantially between Japanese and French Caucasian populations 6.