ABCB1 and glioblastoma: In fact, [11C]tariquidar behaved very similar in rodents and humans in terms of its brain distribution as [11C]erlotinib [42, 43], a radiolabeled epidermal growth factor receptor (EGFR) targeted tyrosine kinase inhibitor, which is also a dual ABCB1/ABCG2 substrate and which failed in a phase II trial in patients with glioblastoma multiforme [44].