Abstract
Tumor lysis syndrome (TLS) is a critical oncologic emergency characterized by metabolic disturbances resulting from rapid cancer cell lysis. Rasburicase, a recombinant urate oxidase, is the primary treatment for hyperuricemia in TLS but poses a risk for methemoglobinemia in patients with glucose 6-phosphate dehydrogenase (G6PD) deficiency. We present the case of a 59-year-old male with diffuse large B-cell lymphoma (DLBCL) who developed spontaneous TLS. Rasburicase was administered, successfully reducing uric acid levels, but the patient subsequently experienced cyanosis, hypoxia, and hemolytic anemia. Methemoglobinemia and G6PD deficiency were confirmed, highlighting the need for early identification of G6PD deficiency before rasburicase use. This case emphasizes the importance of prompt recognition and management of rasburicase-induced methemoglobinemia, especially in high-risk populations.