As medical research develops, more and more attention is being focused on the study of elemental alterations in cancer patients, not only as a marker of the disease, but also as a possible complication of the disease. This study aims to investigate changes in the levels of essential and toxic trace elements in patients who completed antitumor therapy for malignant neoplasms. A retrospective study was conducted among children and adolescents aged 4 to 17 years at a single center. A total of 214 patients were enrolled in this study, with an equal distribution of 107 patients in both the remission group after undergoing therapy for hematologic malignancies and the group who completed therapy for solid tumors. The results of the study of hair samples and blood serum showed that the elemental profile of patients after antitumor therapy has both similar patterns and distinctive features depending on the histological type of tumor. Our data demonstrate that patients with solid tumors showed somewhat higher accumulation of toxic metals compared to samples from patients with hematopoietic tumors, and neoplasms of the hematopoietic system are characterized by more pronounced alterations in the composition of essential elements in hair and blood serum. Nevertheless, serious specific alterations in elemental homeostasis depending on the histologic structure have not been reported. The findings obtained highlight the importance of careful monitoring of homeostasis parameters to prevent the development of complications of antitumor therapy associated with elementary homeostasis.