[Pharmacokinetic issues on cancer pharmacotherapy]

Efficacy of cancer pharmacotherapy depends upon drug exposure to the body and responsiveness of the tumor to the drug treatment. Drug exposure is determined by pharmacokinetics and dose, whereas responsiveness is intrinsically variable by tumor heterogeneity. Molecular targeting drugs are used as promising therapy for cancers, and most of them are coupled with particular diagnostics which can predict responders and non-responders before treatment. On the other hand, lower drug exposure to the body can lead to insufficient efficacy. A number of important evidences have been published recently on exposure-response relationships for molecular targeting drugs including monoclonal antibodies and small molecules. In this chapter, two examples are presented; anti-HER2 antibody and tyrosine kinase inhibitor. Patients with the lowest trough concentrations of trastuzumab in cycle 1 showed shorter overall survival in metastatic gastric cancer study. Efficacy of imatinib in chronic myelogenous leukemia depended on plasma concentration of imatinib, and therapeutic drug monitoring (TDM) of imatinib is expected to improve the therapeutic outcome in CML.