ABCG2, also known as Breast Cancer Resistance Protein (BCRP), is a member of the ATP-binding cassette (ABC) transporter family. It plays a key role in the efflux of a wide range of substrates, including drugs, toxins, and metabolic products, across cellular membranes. ABCG2 is widely expressed in various tissues such as the intestinal epithelium, liver, placenta, kidneys, and blood-brain barrier, where it contributes to the protection of the body by limiting the absorption of harmful compounds. In cancer cells, overexpression of ABCG2 is associated with multidrug resistance, as it can pump out chemotherapy drugs, reducing their efficacy. ABCG2 is also involved in regulating the pharmacokinetics of many therapeutic agents, making it an important target in drug development and cancer treatment strategies.