A personalized chemotherapy treatment regime based on the patient's constitutional genotype can help reduce the risk of severe adverse drug effects (ADRs) such as drug-induced myelosuppression, cardiotoxicity, or ototoxicity. In this project, we will analyze around 500 Swedish pediatric cancer patients included in Barntumörbanken (BTB) or the Genomic Medicine Sweden Childhood Cancer pilot study (GSM-CC). Our first aim is to identify genetic variants associated with commonly observed ADRs to four groups of chemotherapeutics routinely used in pediatric oncology (methotrexate, platinum compounds, anthracyclines, and ifosfamide and irinotecan). Our second aim is to test a toxicity prediction model, previously developed to predict myelosuppressive toxicity in adult cancer patients1, for its predictive capacity in pediatric patients. Lastly, we want to identify new genetic variants and candidate genes associated with myelosuppression phenotypes (leukopenia, neutropenia, and thrombocytopenia) in the same patient cohort. These findings will be used to further refine our toxicity prediction model for pediatric patients.