Abstract Oral etoposide displays high intervariability and intravariability. Convincing relationships were observed between hematological toxicities and exposure of which total etoposide area under the curve seems the more relevant in routine practice. Linear pharmacokinetics, limited sampling strategies and reduction in variability during concentration-controlled studies argue in favor of therapeutic drug monitoring. However, such reduction in variability should be confirmed after oral administration. For these reasons, such practice can be considered as 'potentially useful'. Further studies using Bayesian approach are nevertheless needed to definitely state regarding the level of evidence therapeutic drug monitoring of oral etoposide.