If you’ve recently started chemotherapy treatment, you may have been warned about side effects that sound scary, and feel even scarier at 2 a.m. when your stomach flips or your heart seems to race. One of those urgent complications is Tumor lysis syndrome.
Tumor lysis syndrome, an oncologic emergency (often called TLS), can move fast. The hard part is that early signs can look like “normal chemo stuff.” The brave thing is not to tough it out, it’s to notice what’s changing and speak up.
This guide explains what TLS is, the early symptoms people often miss, the key lab tests (uric acid, potassium, phosphorus), and the moments when it’s safer to go straight to the ER.
What tumor lysis syndrome is (and why it can turn serious quickly)
Tumor lysis syndrome happens when a large number of cancer cells break apart over a short time, often after starting chemotherapy treatment, targeted therapy, immunotherapy, radiation, or even high-dose steroids. When those cells burst, they spill their contents into the blood. Your body usually clears waste in a steady, controlled way. Tumor lysis syndrome is different. It is like dumping a full trash bag into a kitchen sink all at once, the drain clogs.
Those released substances can push blood chemistry out of balance, especially uric acid, potassium, and phosphate. If levels rise too quickly, the kidneys can struggle, the heart’s rhythm can be affected, and the nervous system can get irritated.
Tumor lysis syndrome is most common with hematologic malignancies and cancers with a high tumor burden (a lot of disease in the body), such as Non-Hodgkin lymphoma, acute lymphoblastic leukemia, and other hematologic malignancies, but it can happen with solid tumors too, especially when treatment works well and many cells die at once. It can also happen “spontaneously,” before therapy starts.
If you want a plain-language overview that matches what many cancer centers teach, the Canadian Cancer Society’s tumor lysis syndrome page lays out the basics clearly.
Early symptoms of tumor lysis syndrome you might notice at home
Tumor lysis syndrome doesn’t always announce itself with one dramatic symptom. Sometimes it starts as a vague feeling that something is off. If you’re in treatment, trust that instinct. Your job isn’t to diagnose it, it’s to report what you’re feeling.
Early symptoms can include stomach and bowel changes, like Nausea and vomiting, diarrhea, or a sudden loss of appetite. Some people describe a restless, flu-like misery, the kind that doesn’t match their usual post-treatment pattern.
As electrolyte abnormalities shift minerals like potassium and phosphate, muscles and nerves complain. You might notice Muscle cramps, twitching, tingling around the mouth, or shaky weakness that feels out of proportion. You may feel unusually irritable or foggy. If calcium drops (often tied to high phosphate), you can get spasms or numbness.
Kidney strain from uric acid buildup can show up quietly at first. Watch for decreased Urine output, very dark urine, new swelling in feet or around the eyes, or sudden weight gain from fluid. Shortness of breath can happen if fluid builds up.
Cardiac arrhythmias deserve respect. Cardiac arrhythmias like a racing heartbeat, chest tightness, or feeling lightheaded can signal potassium trouble, and potassium is one of the most dangerous pieces of TLS.
For a patient-focused explanation of symptoms and diagnosis, the JAMA Oncology patient page on tumor lysis syndrome is a helpful companion read.
Key labs in tumor lysis syndrome: uric acid, potassium, and phosphorus (plus a few others)
Tumor lysis syndrome is confirmed with blood tests using criteria like the Cairo-Bishop criteria to classify the condition. Your care team may check labs often when risk is higher, sometimes several times a day early in treatment. Even if you feel okay, labs can change first. Key labs also include lactate dehydrogenase as a marker of cell turnover.
Here’s what the main tumor lysis syndrome labs mean in real life:
| Lab (blood test) | What “high” (or low) can do | What it can feel like |
|---|---|---|
| Hyperuricemia (uric acid) | Can form crystals and cause acute kidney injury | Flank pain (sometimes); less urine (more often); nausea; fatigue |
| Hyperkalemia (potassium) | Can trigger dangerous heart rhythm changes | Palpitations; weakness; tingling; faintness; chest discomfort |
| Hyperphosphatemia (phosphorus) | Can rise fast and cause hypocalcemia; can harm kidneys | Cramps; tingling; muscle spasms; confusion |
| Hypocalcemia (low calcium) | Irritates nerves and muscles; can affect heart | Numbness; twitching; spasms; seizures in severe cases |
| Creatinine (kidney marker) | Shows kidney stress or acute kidney injury | Often no clear symptom early; later less urine; swelling; shortness of breath |
People often focus on uric acid or hyperuricemia because it sounds like gout, but hyperkalemia is the one that can turn into an emergency quickly because of heart effects from high potassium levels. Hyperphosphatemia can contribute to issues like phosphorus buildup alongside hypocalcemia.
If you want a simple medical overview that’s still readable, the Cleveland Clinic’s tumor lysis syndrome guide explains these lab shifts and typical treatments (like IV fluids and uric acid medicines).
When to go to the Emergency Room for tumor lysis syndrome (and what to say when you get there)
There’s courage in not waiting. If you’re at higher risk for tumor lysis syndrome, your oncology team may give you a plan for after-hours symptoms that includes risk stratification, intravenous hydration, or allopurinol. Follow it. But some situations are “emergency room now,” even if you don’t want to be a bother.
Go to the emergency room or call emergency services right away if you have:
- Chest pain, fainting, severe dizziness, new irregular heartbeat, or a fast heartbeat that won’t settle
- Trouble breathing, new or worse shortness of breath, or sudden swelling with rapid weight gain
- Confusion that is new, severe weakness, inability to keep fluids down, or uncontrolled vomiting
- Muscle cramps with tingling or spasms that are worsening
- Seizures
- Very low urine output (especially over half a day), or you can’t pee at all
Also go urgently if you were told you’re high risk for tumor lysis syndrome and you’re within the first days of a new treatment cycle, even if symptoms seem “mild.” TLS is one of those problems where waiting for morning can lead to acute kidney injury.
At the emergency room, say clearly: “I’m being treated for cancer, and I’m worried about tumor lysis syndrome.” If you can, share your diagnosis, your most recent treatment date, and any recent lab results. Emergency teams often move faster when they know tumor lysis syndrome is on the table, starting with intravenous hydration to boost urine output and allopurinol (or rasburicase for high-risk cases) to manage uric acid levels. Severe cases with kidney failure may require dialysis or continuous renal replacement therapy. A practical emergency room-focused summary is available from Emergency Care BC’s TLS clinical resource.
If you’re in remission and starting a new therapy, or restarting treatment after a break, the risk discussion still matters. Remission doesn’t always mean “no risk,” it means the plan is changing again.
Conclusion: Trust your body, and act early
It’s frightening, but it’s also treatable, especially when caught early. Stay vigilant by paying attention to patterns, pee, heart symptoms, and new muscle or thinking changes; monitor uric acid and potassium levels to catch changes early; and don’t ignore a gut feeling that something isn’t right. The quiet, everyday kind of courage is making the call, going in, and letting a team check the labs that can’t be guessed at home for tumor lysis syndrome.
