Tumour Lysis Syndrome: — A Rare but Serious Early Complication

The early symptoms are often not dramatic — nausea, muscle cramps or twitching, unusual fatigue, and less urine than usual. These can feel similar to ordinary chemotherapy side effects, which makes them easy to dismiss. The difference is timing: tumour lysis typically appears within the first few days of starting treatment, and the symptoms tend to worsen rather than follow the predictable rise and fall of ordinary chemo side effects. Report any of these in the first days of treatment rather than waiting to see if they settle on their own.

No. Most patients do not develop it, even with high-risk cancers, because the monitoring and prevention measures your team uses are effective. Whether it occurs depends on your cancer type, the size and sensitivity of the tumour, and your kidney function at the start of treatment. Your oncologist will have assessed your individual risk before the first cycle. Not developing it is the expected outcome — the symptoms are worth knowing so you can act quickly if they do appear, not as a source of ongoing anxiety.

It means cancer cells are dying rapidly, which is what chemotherapy is designed to do. But it is a complication to be managed — not a marker that treatment is working better than if you had not developed it, and not a measure of how well it will ultimately work. Patients who do not develop tumour lysis syndrome are not getting a weaker response. Your response to treatment will be measured by scans and blood markers at later timepoints, not by whether this early complication occurred.

Tell your oncology team about every medicine, supplement and herbal preparation you take before treatment begins — not just prescription medicines. Anti-inflammatory painkillers such as ibuprofen and naproxen can reduce blood flow to the kidneys and worsen the kidney stress of tumour lysis syndrome, so they are generally avoided in this period. Your team will tell you which of your regular medicines are safe to continue, which to pause, and what to take instead for pain or fever if needed during those first days.

The highest-risk period is the first few days after starting chemotherapy, according to NCCN guidance, though monitoring typically continues through the early days of each new treatment cycle. After the first cycle, your team will have a clearer picture of how your tumour responds and can adjust the monitoring accordingly. The risk is greatest at the very start — once that initial window has passed without incident, later cycles carry a lower risk, but your team will continue to monitor your blood results throughout treatment.