UGT3A2 is a UDP-glycosyltransferase that catalyzes phase II biotransformation through glycosylation rather than the glucuronidation typical of other UGT subfamilies. Unlike UGT1 and UGT2 families that use UDP-glucuronic acid, UGT3A2 uniquely utilizes UDP-glucose and UDP-xylose as cosubstrates to conjugate lipophilic compounds, enhancing their water solubility and excretion 1. A critical phenylalanine residue at position 391 confers this distinctive sugar selectivity 2. UGT3A2 exhibits robust catalytic activity against polycyclic aromatic hydrocarbons (PAHs)—potent environmental carcinogens—with UDP-xylose supporting up to 4.4-fold higher activity than UDP-glucose 3. This enzyme is distinctly expressed in aerodigestive tract tissues (lung, esophagus) rather than liver, positioning it as a critical first-line detoxifier in PAH-exposed tissues 3. Clinically, missense variants (MAF ≥0.005) significantly impair PAH metabolism, with some variants showing 362-fold reduced activity, potentially elevating individual susceptibility to PAH-related cancers 4. Additionally, UGT3A2 somatic mutations occur in ~18% of cancers, with UGT3A2 among the most frequently mutated UGT genes (255 mutations across 10,069 tumors), suggesting roles in drug metabolism and cancer progression 5. These findings indicate UGT3A2 functions as a specialized protective enzyme in extrahepatic tissues exposed to environmental toxins.