Many drugs currently used for anti-cancer therapy demonstrate significant inter-individual variability that cannot be normalized using body weight or body surface area. There is an increasing amount of evidence in the scientific literature describing the use of therapeutic drug monitoring (TDM) to inform dosing of these drugs can lead to more effective treatment. This presentation will discuss the scientific literature addressing inter-individual variability of these drugs, the concept of maximum tolerated dose (MTD), and why an approach using maximum tolerated exposure (MTE) might be a better way to manage some chemotherapeutic drugs. Specific examples of TDM in oncology will be discussed including 5-fluorouracil, taxanes, and tyrosine kinase inhibitors.