[Impact of cancer muscle mass loss on anticancer treatment toxicities]

Administration of targeted therapies as a flat dose and administration of chemotherapy based on body surface area do not take into account several important sources of inter-individual variation. These variations could be responsible partially for the occurrence of toxicity. Furthermore, the availability of high-resolution CT images in the record of cancer patients, from which key body composition information may be derived, allows us to study the relationship between body composition and toxicity. If many studies have highlighted this relationship, the mechanisms are not completely understood. There are some arguments for a pharmacokinetic hypothesis: low muscle mass i.e. sarcopenia, is associated with high drug plasma concentration which in turn is associated with an increase in the incidence of toxicity. The other hypothesis is that sarcopenic patients have a higher susceptibility to medical events leading to an increase in chemotherapy toxicity. This concept of frailty was widely described in studies in the elderly. This body composition analysis opened a huge area of research and many questions still need to be resolved. Defining the cut-offs values for low muscle mass is important since in most of the studies, the cut-offs values used were defined using survival studies. What could be the physiological link between cut-off values defined by survival studies and chemotherapy toxicities? Authors also used the median values, the level which predicted the occurrence of toxicity most accurately and sometimes the measure of the psoas. The final and crucial question is the capacity of reducing toxicity by body composition based dosing.