Substrates of BCRP (ABCG2) include glutathione and steroid hormones (Mao & Unadkat, 2005) as well as some anti-tumor chemotherapeutic agents like methotrexate, mitoxantrone, and topotecan (Huang & Sadée, 2006), which overlap with those of P-gp (Staud & Pavek, 2005). Here, PGP is linked to neoplasm.