🩺 Tumor Lysis Syndrome (TLS): Emergency Oncologic Complication for the USMLE
Tumor Lysis Syndrome (TLS) is one of the most dangerous oncologic emergencies and is commonly tested on the USMLE due to its classic lab findings, urgent intervention requirements, and systemic impact.
It often arises after chemo or radiation therapy, especially in rapidly growing tumors (e.g., leukemia, lymphoma).
🧪🔬 Pathophysiology of TLS
When large numbers of cancer cells are destroyed rapidly, they release intracellular contents into the bloodstream.
| Released Substance | Effect |
|---|---|
| Potassium (K⁺) | → Hyperkalemia |
| Phosphate (PO₄³⁻) | → Hyperphosphatemia |
| Nucleic acids → uric acid | → Hyperuricemia, AKI |
| Calcium (Ca²⁺) | → Hypocalcemia (binds phosphate) |
📌 USMLE Tip: Look for high K⁺, high phosphate, low Ca²⁺, high uric acid in labs.
🧪 Classic Lab Findings
| Lab Marker | Change |
|---|---|
| Potassium (K⁺) | ↑ |
| Phosphate (PO₄³⁻) | ↑ |
| Uric Acid | ↑ |
| Calcium (Ca²⁺) | ↓ |
| Creatinine | ↑ (AKI) |
💡 Risk Factors
Hematologic malignancies (e.g., Burkitt lymphoma, ALL)
Large tumor burden
High sensitivity to chemotherapy
Pre-existing renal dysfunction
🚨 Clinical Signs
Nausea, vomiting
Lethargy, confusion
Muscle cramps, tetany
Seizures (from hypocalcemia)
Arrhythmias (from hyperkalemia)
💊 USMLE Emergency Management
| Step | Treatment |
|---|---|
| 1 | IV hydration |
| 2 | Allopurinol (prevention) or Rasburicase (treatment) |
| 3 | Calcium gluconate (for symptomatic hypocalcemia) |
| 4 | Treat hyperkalemia (standard emergency steps) |
| 5 | Dialysis (if refractory or renal failure) |
💥 Rasburicase is often the drug of choice in established TLS (USMLE favorite!)
🎯 USMLE Clinical Vignette Sample
A 9-year-old boy with new-onset ALL starts induction chemotherapy. Within 24 hours, he becomes lethargic. Labs show K⁺ 6.4, uric acid 12.1, phosphate 6.0, calcium 6.8. What’s the next best step?
✅ Answer: Start aggressive IV fluids and rasburicase. Monitor for renal failure and electrolyte abnormalities.
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