ABCG2 is an ATP-dependent efflux transporter of the ABC family that actively extrudes diverse substrates including xenobiotics, endogenous metabolites, and drugs from cells 1. The transporter mediates urate excretion in both renal and extrarenal tissues, functioning as a physiological urate exporter 2. ABCG2 regulates porphyrin homeostasis by exporting protoporphyrin IX from mitochondria to cytosol and facilitating heme efflux 3. The transporter also exports steroid conjugates like estrone 3-sulfate and mediates riboflavin and biotin secretion into milk 4. In macrophages, ABCG2 exports itaconate from the cytosol, limiting TFEB-dependent lysosomal biogenesis and suppressing antibacterial innate immunity 5. Clinically, ABCG2 confers multidrug resistance by effluxing chemotherapeutic agents including mitoxantrone, doxorubicin, and camptothecin 1. The transporter is highly expressed in cancer stem cell populations and serves as a marker of chemotherapy resistance 6. Genetic polymorphisms in ABCG2, particularly c.421C>A (rs2231142), exhibit significant interethnic variability and affect transporter activity and drug response 7. In colorectal cancer, ABCG2 underexpression correlates with altered signaling pathways involved in carcinogenesis, though expression does not predict patient survival 8. ABCG2 also contributes to blood-brain barrier function by limiting xenobiotic penetration and protects the fetus through placental drug efflux.