Tumor lysis syndrome (TLS): What it is
Tumor lysis syndrome is a medical emergency that can happen when many cancer cells break down at the same time. When this happens, substances inside the cells are released into your blood.
This sudden release can cause high levels of potassium, phosphate, and uric acid, and low levels of calcium. These changes can strain your kidneys and affect your heart, muscles, and nerves.
TLS is most common in blood cancers, such as some leukemias and lymphomas, but it can happen with many cancer types.
What causes tumor lysis syndrome?
TLS most often happens soon after cancer treatment starts, especially when treatment kills cancer cells quickly. It can occur within hours to a few days after chemotherapy or other anti-cancer therapies.
- Chemotherapy and targeted therapies
- Immunotherapy or certain antibody treatments
- Steroids or radiation therapy
Rarely, TLS can happen on its own before treatment, especially in fast-growing blood cancers.
Who is at higher risk?
Your risk is higher if you have:
- A fast-growing cancer
- A large number of cancer cells in your body (large tumor or cancer spread)
- Blood cancers with very high white blood cell counts
- Kidney problems or dehydration
- High uric acid or high LDH levels before treatment
Your oncology team will review your cancer type, lab results, and treatment plan to estimate your risk.
What are the symptoms?
Some people have no symptoms at first. When symptoms do happen, they can include:
- Nausea, vomiting, or diarrhea
- Loss of appetite and feeling very tired
- Decreased urination or dark urine; blood in the urine
- Muscle cramps, twitching, or stiffness
- Irregular or fast heartbeat, or chest discomfort
- Confusion, seizures, or fainting
Without quick care, TLS can lead to heart rhythm problems and kidney injury. Getting help right away lowers the risk of serious complications.
How do clinicians check for TLS?
If your team suspects TLS, they will do blood tests to measure potassium, phosphate, uric acid, calcium, and kidney function. They may also check your heart rhythm and monitor your urine output.
Doctors diagnose TLS based on your symptoms and lab results. Frequent repeat tests help guide care.
Can TLS be prevented?
Many cases can be prevented or caught early with planning and close monitoring. Your team may recommend prevention steps before and during treatment if your risk is moderate or high.
- IV fluids: Extra fluids help protect your kidneys and flush out waste.
- Medicines to lower uric acid: Options include allopurinol, rasburicase, or sometimes febuxostat. Ask your team which, if any, is right for you.
- Frequent checks: Monitoring your heartbeat, urine output, and blood tests helps catch changes early.
Even with prevention, TLS can still occur. Planning ahead and regular lab checks help keep you safe.
How is TLS treated?
TLS is treated in the hospital so you can be watched closely and treated quickly. Treatment aims to protect your kidneys and safely correct blood levels.
- IV fluids: To support kidney function and increase urine flow.
- Medicines for electrolytes: Treatments may be used to lower potassium, manage high phosphate, and carefully adjust calcium.
- Uric acid–lowering medicines: These help remove or reduce uric acid.
- Dialysis (kidney replacement therapy): Some people need temporary dialysis if kidney function drops or electrolytes stay unsafe despite medicines.
With fast treatment, most people recover without long-term problems.
How you can partner with your care team
- Ask about your personal TLS risk before starting a new cancer therapy.
- Know your plan for prevention and lab monitoring.
- Drink fluids as advised by your team, unless you have fluid limits.
- Report new symptoms right away, especially in the first week of a new treatment.
Key takeaways
- TLS happens when many cancer cells break down at once, changing blood levels of potassium, phosphate, uric acid, and calcium.
- It is most common in some leukemias and lymphomas but can occur with many cancers.
- Prevention with IV fluids, medicines, and close monitoring can lower risk.
- TLS is treatable, especially when recognized and managed quickly.
Last reviewed: 2025-11-28
