ABCG2 and neoplasm: The HIV-protease inhibitors (HIV-PIs) are substrates/inhibitors of the ABC transporters ABCB1, ABCG2, ABCC1, and ABCC2 (Lee et al, 1998); induce and/or select for ABCB1 in human tumour cells (Perloff et al, 2000; Vishnuvardhan et al, 2003); and sensitise cells to chemotherapeutics such as vincristine, vinblastine, and doxycycline in an HIV-PI-dependent manner.