Tumor Lysis Syndrome (TLS)

Recognition, risk stratification, prevention with allopurinol and rasburicase, and management of an oncologic metabolic emergency

Key Points

• Tumor lysis syndrome results from massive release of intracellular contents (uric acid, potassium, phosphate) following rapid tumor cell death — most commonly after initiating chemotherapy for high-burden hematologic malignancies.
• TLS is classified by Cairo-Bishop criteria into laboratory TLS (≥2 metabolic abnormalities) and clinical TLS (laboratory TLS plus renal failure, arrhythmia, seizure, or death).
• Hyperuricemia, hyperkalemia, hyperphosphatemia, and secondary hypocalcemia are the four cardinal metabolic derangements — hyperkalemia and hypocalcemia carry the highest immediate mortality risk (cardiac arrhythmia, tetany, seizures).
• Risk-stratified prophylaxis is the cornerstone: allopurinol for intermediate-risk patients; rasburicase for high-risk patients and established TLS.
• Rasburicase is absolutely contraindicated in patients with G6PD deficiency — it causes life-threatening oxidative hemolysis in this population.
• Aggressive IV hydration (2–3 L/m²/day) and close electrolyte monitoring every 4–8 hours are mandatory for all high-risk patients starting treatment.

Pathophysiology and Definition

Tumor lysis syndrome (TLS) occurs when a large number of malignant cells die rapidly — most commonly triggered by the initiation of cytotoxic chemotherapy, but also by radiation, targeted therapy, corticosteroids alone, CAR-T cell therapy, and, in rare cases, spontaneously in rapidly proliferating tumors. As tumor cells lyse, they release massive quantities of intracellular contents into the bloodstream, overwhelming the body's normal homeostatic mechanisms: **1. Hyperuricemia:** Nucleic acids (DNA, RNA) released from lysed cells are catabolized to hypoxanthine, then xanthine, then uric acid…

Risk Stratification

Risk stratification guides prophylaxis intensity and monitoring frequency. The risk of TLS depends on three interacting factors: tumor bulk and proliferative rate, tumor sensitivity to the intended treatment, and patient-specific factors (pre-existing renal dysfunction, baseline elevated uric acid, volume depletion). **HIGH RISK (>5% risk of clinical TLS) — rasburicase prophylaxis recommended:** - **Burkitt lymphoma / Burkitt-like lymphoma**: the single highest-risk diagnosis; risk of TLS approaches 30–40% without prophylaxis; hyperproliferative (Ki-67 ~100%) with exquisite chemosensitivity…

Prevention — Hydration, Allopurinol, and Rasburicase

**1. IV Hydration:** Aggressive hydration is the foundation of TLS prophylaxis for all intermediate- and high-risk patients. Hydration increases renal blood flow, enhances glomerular filtration, and promotes urinary uric acid and electrolyte excretion. - **Recommended rate**: 2–3 L/m²/day (approximately 150–200 mL/hour in an average adult) of isotonic saline (normal saline is preferred; hypotonic solutions are avoided) - Begin 24–48 hours before chemotherapy initiation in high-risk patients - Target urine output: ≥2 mL/kg/hour in adults; ≥3 mL/kg/hour in children - **Urinary alkalinization…

Treatment of Established TLS

When TLS develops despite prophylaxis, management requires aggressive simultaneous correction of multiple metabolic derangements. ICU-level monitoring is required for clinical TLS. **1. Hyperuricemia:** - Rasburicase 0.2 mg/kg IV (if not already initiated and no G6PD deficiency) - Aggressive hydration to maintain urine output ≥2–3 mL/kg/hour - Allopurinol as adjunct or alternative if rasburicase is contraindicated **2. Hyperkalemia (most immediately dangerous):** Potassium ≥6 mEq/L requires urgent intervention. Approach is layered: - **Continuous cardiac monitoring** — obtain 12-lead ECG…

Special Situations — Venetoclax and Spontaneous TLS

**Venetoclax-Associated TLS:** Venetoclax (Venclexta), a BCL-2 inhibitor used in CLL, AML, and other hematologic malignancies, has a distinctive TLS profile that prompted the FDA to require a structured risk assessment and dose ramp-up protocol for all patients before initiating therapy. Venetoclax works by rapidly inducing apoptosis in BCL-2-dependent malignant cells. In patients with high CLL tumor burden (lymph node diameter >10 cm, ALC >25,000/μL, or lymph node 5–10 cm combined with ALC ≥25,000/μL), TLS risk is high. The mandatory venetoclax ramp-up schedule (20 mg → 50 mg → 100 mg → 200…