Sunitinib as a multikinase inhibitor is indicated for the treatment of unresectable and/or metastatic malignant gastrointestinal stromal tumor (GIST) in adults after failure of imatinib treatment due to resistance or intolerance. Another indication is the treatment of advanced/metastatic renal cell carcinoma (MRCC) or treatment of unresectable or metastatic, well-differentiated pancreatic neuroendocrine tumours (pNET) with disease progression in adults. There is also clinical experience with the use of sunitinib in pediatric oncology patients, e.g. with refractory solid tumors, GIST. The article describes the course of treatment of osteosarcoma in a pediatric patient in whom sunitinib was administered based on the results of genetic testing and proteomics. Skin discoloration, a reversible adverse effect, occurred in connection with the use of sunitinib. This adverse effect of sunitinib is mentioned for the first time in the Czech literature in a pediatric patient.