PEGASUS aims to test acceptability and feasibility of studying phenoconversion (the change in metabolism phenotype) using probe medications in a paediatric oncology patient population. The study will be conducted in patients (6-25 years of age) with Hodgkin lymphoma or non-Hodgkin lymphoma as exemplar cohort, but with the understanding that cancer-directed and supportive care medicines of the CYP3A4, CYP2C19, and CYP2D6 metabolic pathways are commonly utilised for the treatment of many paediatric, adolescent, young adult, and adult cancers. The study involves administration of the probe medication at timepoints which align with pre-determined hospital visits for the treatment of lymphoma and subsequent blood draws to measure the metabolism of the probe medications. The acceptability and feasibility of this study will inform future studies in phenoconversion within the paediatric cancer population to direct more personalised precision medicine.