“Fatigue is the most commonly reported symptom in children and adolescents during and after treatment for cancer. Fatigue is associated with decreased quality of life and may contribute to decreased physical function and impede normal childhood development. Currently, the only validated way to measure fatigue is through collection of self-reported data which may not be feasible for all children, specifically younger or sicker children, or those with lower reading levels. Proxy (i.e., parent) reports are often used as substitute measures but may not replace a child’s own report. In the precision medicine era, identifying biomarkers for fatigue would be beneficial in screening for and applying interventions to address this common symptom. A metabolomic approach to unraveling symptom experiences is promising as it allows for investigation of multiple metabolites and pathways at once and can provide insight into the physiological status of an individual at any one point in time.”