Tumor lysis syndrome (TLS) is a potentially life-threatening condition that occurs when a large number of cancer cells die rapidly, spilling their contents into the bloodstream. This sudden flood of intracellular material overwhelms the body’s ability to process it, leading to dangerous shifts in blood chemistry that can damage the kidneys, disrupt the heart’s rhythm, and cause seizures. It most commonly happens within the first few days after starting chemotherapy for fast-growing blood cancers like acute leukemia and aggressive lymphomas.
How Tumor Lysis Syndrome Happens
Every cell in the body contains potassium, phosphorus, and molecules called purines (building blocks of DNA). Normally, cells die and get replaced at a manageable pace, and the body clears these substances without trouble. In TLS, a powerful cancer treatment kills millions of tumor cells at once. All those cells burst open simultaneously, releasing their contents into the blood far faster than the kidneys can filter them out.
This creates a chain of problems. Potassium levels spike, which is dangerous because potassium controls the electrical signals that keep the heart beating in a steady rhythm. Phosphorus levels rise sharply, and excess phosphorus binds to calcium in the blood, pulling calcium levels down. Low calcium can cause muscle cramps, numbness, and seizures. Meanwhile, the purines released from dying cells get broken down into uric acid. When uric acid builds up faster than the kidneys can excrete it, it can crystallize inside the kidney’s tiny tubes and cause acute kidney failure.
Who Is Most at Risk
TLS risk depends on two main factors: how fast the cancer cells are dividing and how sensitive they are to treatment. Cancers that grow quickly have enormous numbers of cells ready to be killed all at once, which means more cellular debris flooding the bloodstream. Blood cancers carry the highest risk because they tend to be both fast-growing and highly responsive to chemotherapy.
The cancers most commonly linked to TLS include:
- Burkitt lymphoma (especially advanced stages), one of the fastest-growing human tumors
- Acute lymphoblastic leukemia, particularly when white blood cell counts exceed 100,000 per microliter
- Acute myeloid leukemia with very high white blood cell counts
- Diffuse large B-cell lymphoma with bulky tumors larger than 10 cm
Solid tumors like breast or lung cancer rarely cause TLS, though it can happen in unusual cases. Slow-growing blood cancers such as chronic lymphocytic leukemia and multiple myeloma also fall into the low-risk category. Beyond cancer type, other factors that raise risk include pre-existing kidney problems (since the kidneys are less able to clear the surge of waste), dehydration, and large overall tumor burden.
Symptoms to Watch For
TLS typically develops 12 to 72 hours after the first dose of chemotherapy, though it can occasionally occur before treatment starts if the cancer is growing and dying on its own fast enough. Early symptoms are often vague: nausea, fatigue, and a general feeling of being unwell. As the electrolyte imbalances worsen, more specific signs appear.
High potassium can cause muscle weakness, tingling sensations, and an irregular heartbeat. In severe cases it leads to cardiac arrest. Dropping calcium levels may trigger muscle twitching, cramping, or numbness around the mouth and fingertips. If uric acid crystals begin clogging the kidneys, urine output drops noticeably. Seizures can occur when the electrolyte shifts become severe enough to affect the brain. Because these changes can escalate quickly, patients at risk for TLS have their blood drawn frequently in the first several days of treatment, sometimes every 6 to 8 hours, to catch shifts before they become dangerous.
How Doctors Classify It
Doctors use a framework called the Cairo-Bishop criteria to classify TLS into two stages. Laboratory TLS means that blood tests show at least two of the following abnormalities within three days before or seven days after starting treatment: uric acid at or above 8 mg/dL, potassium at or above 6 mEq/L, phosphorus above normal limits, or calcium dropping below normal. A 25% change from baseline in any of these values also counts.
Clinical TLS is the more serious stage. It means those lab abnormalities are present and the patient has developed at least one major complication: kidney failure, a cardiac arrhythmia, or a seizure. The distinction matters because clinical TLS requires more aggressive intervention and carries a significantly higher risk of death.
Prevention Strategies
Because TLS can progress rapidly once it starts, prevention is the primary focus. Before chemotherapy begins, the medical team assesses each patient’s risk level and tailors a prevention plan accordingly.
Aggressive hydration is the cornerstone. The goal is to keep the kidneys flushing waste as efficiently as possible by maintaining high urine output, generally 70 to 100 mL per square meter of body surface area per hour. In practice, this means patients receive large volumes of IV fluids, typically 2 to 3 liters per square meter of body surface per day, starting before chemotherapy and continuing until the tumor burden has decreased and blood markers normalize.
For patients at low or intermediate risk, a medication that blocks uric acid production is given before and during chemotherapy. It works by shutting down the enzyme in the liver that converts purine breakdown products into uric acid, reducing the chance of kidney-damaging crystals forming. For high-risk patients, a different approach is used: an enzyme given by IV that directly breaks down uric acid already circulating in the blood, converting it into a substance that is 5 to 10 times more soluble and far easier for the kidneys to excrete. This option works faster and more aggressively, but it is not safe for patients with certain inherited enzyme deficiencies that make them prone to a type of anemia.
These two medications are not used together because they work against each other. The first prevents uric acid from being made, which removes the raw material the second one needs to do its job.
Treatment When TLS Develops
If TLS develops despite preventive measures, treatment intensifies. IV hydration is ramped up, often delivered through a central line for faster, higher-volume access. The uric acid-lowering enzyme is started immediately if it was not already being used. Potassium and calcium levels are corrected with targeted interventions, and any external sources of potassium (including certain IV solutions and supplements) are stopped.
Kidney function is monitored closely. If the kidneys can no longer keep up with the metabolic load, dialysis becomes necessary to mechanically filter the blood and restore safe electrolyte levels. This is more likely in patients who already had some degree of kidney impairment before treatment began. Once the wave of cell death subsides and the body catches up with clearance, the electrolyte disturbances typically resolve, but kidney damage can persist if intervention comes too late.
TLS With Newer Cancer Therapies
TLS was historically associated almost exclusively with traditional chemotherapy, but newer targeted cancer drugs have changed the landscape. Some of these agents are extremely effective at killing specific cancer cell types, which means they can trigger massive, rapid cell death even in cancers that were previously considered lower risk. Expert panels have noted that older TLS guidelines did not account for these potent newer treatments, and updated consensus recommendations now incorporate them into risk assessments. If you are starting any new cancer therapy, your medical team will evaluate your specific TLS risk based on the type of cancer, the treatment being used, kidney function, and tumor size.