SELENBP1 is a copper-dependent thiol oxidase that catalyzes the oxidation of methanethiol and other volatile sulfur compounds (VSCs) to hydrogen peroxide, hydrogen sulfide, and formaldehyde 1. Contrary to its name, selenium binding is not required for enzymatic activity; instead, copper ions are essential cofactors 1. SELENBP1 is particularly abundant in tissues exposed to VSCs, including colon, liver, and lung, where it contributes to degradation of gut microbiome-derived and food-derived malodorous compounds 1. Beyond volatile sulfur compound metabolism, SELENBP1 modulates cellular bioenergetics by affecting mitochondrial function and oxidative phosphorylation in prostate cancer cells 2. In colorectal cancer, SELENBP1 downregulation is associated with poor prognosis and altered tumor immune infiltration, suggesting roles in immunotherapy response 3. SELENBP1 is progressively decreased during lung squamous cell carcinogenesis and serves as a biomarker for early cancer detection 4. In kidney disease, SELENBP1 protects against fibrosis through hydrogen sulfide generation via methanethiol metabolism 5. Clinically, SELENBP1 deficiency causes extraoral halitosis due to impaired methanethiol oxidation. Its downregulation represents an early event in multiple cancers and correlates with immunotherapy sensitivity, positioning SELENBP1 as a promising prognostic biomarker and potential therapeutic target.