What to expect from a PET-CT scan for cancer of unknown primary

A small amount of radioactive tracer is given, usually through a vein. Areas using more tracer can appear differently from surrounding tissue, while the CT part shows anatomy and location. Infection, inflammation and some normal tissues can also take up tracer, so a scan finding is not automatically cancer.

With cancer of unknown primary, the scan may help identify a likely origin, show where disease is present or select a safer and more useful area for biopsy. It may not find the original site, and the result is considered with pathology, examination and other imaging.

Follow the centre's instructions about fasting, drinking water and medicines. Tell staff about diabetes, pregnancy or breastfeeding, kidney problems, recent illness and difficulty lying still. Wear warm, comfortable clothing and avoid strenuous activity beforehand if instructed, because muscle activity can affect images.

After the injection, you usually rest quietly while the tracer circulates, then lie still during imaging. The scan is not usually painful apart from the injection, but the room can feel enclosed. Limit close contact with vulnerable people for the period advised by the imaging team.

Tell staff immediately about pain, swelling or rash at the injection site, dizziness or feeling unwell. After leaving, contact the centre for worsening symptoms or concerns about the injection. A radiologist will interpret the images and your cancer team will explain what happens next.

Seek urgent help for severe breathing difficulty, facial swelling, collapse or chest pain. Do not wait for the scan report if you develop a serious symptom.

Ask what the scan is intended to clarify, how to manage diabetes medicines, whether contrast is planned, when results will be discussed, and what further imaging or biopsy might follow. Ask whether any temporary radiation-safety instructions apply to your household.