Tumor lysis syndrome (TLS) is an oncologic emergency resulting from the rapid destruction of large numbers of malignant cells, either spontaneously or following initiation of cytotoxic therapy. When tumor cells lyse, they release massive quantities of intracellular contents into the bloodstream, including potassium, phosphorus, nucleic acids, and uric acid. Nucleic acids are metabolized to uric acid by xanthine oxidase in the liver. The sudden surge of uric acid overwhelms renal excretion capacity, and uric acid crystals precipitate in the renal tubules, causing obstructive uropathy and acute kidney injury. Elevated phosphorus binds to serum calcium, forming calcium phosphate deposits in tissues and causing secondary hypocalcemia. The resulting electrolyte derangements - hyperkalemia, hyperphosphatemia, hypocalcemia, and hyperuricemia - create a cascade of life-threatening complications including fatal cardiac dysrhythmias from hyperkalemia and seizures or tetany from hypocalcemia.