Why does childhood cancer cause unexplained fever?

Some childhood cancers release chemical signals that activate the immune system. Those signals can reset the body's temperature response and lead to fever without an obvious infection. Cancer can also affect bone marrow, where blood cells are made. Fewer healthy infection-fighting cells may make infections harder to spot, while abnormal cells and inflammation can add to fever.

A fever has many possible explanations in children, including common infections and inflammatory conditions. The pattern matters: clinicians ask when it began, how it changes, whether it returns, and whether there are signs such as tiredness, pallor, bruising, pain, or reduced appetite.

Record the child's temperature, how it was measured, the time of each reading, and any accompanying symptoms. Offer fluids if the child can drink, allow rest, and use fever medicine only as directed for that child. Arrange a medical assessment for fever that keeps returning, lasts longer than expected, or occurs with other concerning changes. A clinician may examine the child and decide whether blood tests or other checks are needed.

Seek urgent medical care if a child with fever is difficult to wake, has trouble breathing, has a seizure, appears severely unwell, cannot keep fluids down, or shows unusual bleeding or widespread bruising. Prompt assessment is also needed when fever occurs during or soon after cancer treatment, because infection can become serious quickly when immune defences are reduced.

Ask what fever pattern should be recorded, whether medicines could alter the readings, which warning signs require immediate help, and whether the child needs blood-count testing or review by a paediatric oncology team.