Lymphoma is the third leading cause of malignant neoplasms (MNs) in children. Childhood lymphoma is characterized by the prevalence of highly aggressive variants with high proliferation activity and rapid tumor dissimilation. Prolonged diagnosis becomes a reason of advanced-stage therapy. Despite the good results of long-term survival rate in patients, exceeding 90% even with late (III-IV) stages of lymphomas, the persistence of pathogenic (including multi-drug resistant) microorganisms in the patient's body becomes a major therapeutic problem, contamination of which occurs during the patient's stay in various medical organizations at the stage of diagnostics. The case reports of fatal infectious complications with the development of sepsis caused by polyresistant microorganisms in 2 children with anaplastic large cell lymphoma stage IV are presented in this article. Both case reports are unfavourable, despite the use of all medications and effective treatments. The analysis of diagnostic errors and necessity of cancer alarm generation in medical staff and patients' parents will make it possible to reduce the duration of diagnosis and probability of contamination of patient’s body with multi-resistant flora.