This dose dependency in [11C]erlotinib clearance is in good agreement with a dose escalation study of i.v. erlotinib in cancer patients, in whom a decrease in clearance was observed with increasing erlotinib dose.25 The mean unbound plasma concentration of unlabeled erlotinib at the time of the PET scan (0.18 μM) was in a similar range as the in vitro Km value for erlotinib transport by OATP2B1 (0.32 μM). Here, SLCO2B1 is linked to cancer.