Clinical meaning
Tumor lysis syndrome (TLS) is an oncologic emergency that occurs when rapid destruction of tumor cells releases intracellular contents (potassium, phosphate, nucleic acids) into the bloodstream, overwhelming the body's homeostatic mechanisms. Nucleic acids from lysed cells are metabolized by xanthine oxidase to uric acid, which is poorly soluble in acidic urine. When uric acid production exceeds renal excretion capacity, uric acid crystals precipitate in the renal tubules and collecting ducts, causing urate nephropathy — an obstructive crystalline nephropathy that produces acute kidney injury with oliguria. Simultaneously, released phosphate binds with calcium to form calcium phosphate crystals, which deposit in renal tubules (nephrocalcinosis) and soft tissues, causing both AKI and symptomatic hypocalcemia (tetany, QT prolongation, seizures). Hyperkalemia from rapid cellular release of potassium is the most immediately life-threatening metabolic derangement, causing cardiac arrhythmias (peaked T waves → loss of P waves → widened QRS → sine wave → cardiac arrest). TLS most commonly occurs with rapidly proliferating, treatment-sensitive malignancies: high-grade lymphomas (Burkitt lymphoma is the prototype), acute lymphoblastic leukemia (ALL), and acute myeloid leukemia with high WBC count. Rasburicase is a recombinant urate oxidase enzyme that converts uric acid to allantoin, which is 5-10 times more soluble than uric acid, dramatically reducing serum uric acid within hours. Unlike allopurinol (which only prevents NEW uric acid formation by inhibiting xanthine oxidase), rasburicase actively degrades EXISTING uric acid, making it far more effective for established or high-risk TLS.