Can a PET scan find cancer?

Many cancer cells use energy differently from surrounding tissue. A PET tracer follows part of that energy use, and the scanner maps where it collects. CT images show the location and structure of a finding. This combination may help identify a primary site, assess lymph nodes or look for disease in other regions. Some cancers are less visible on PET, and infection or inflammation can also appear active. A biopsy or another test may still be needed.

Ask why the scan was requested and what question it is meant to answer. Follow preparation instructions carefully, especially those concerning food, activity and medicines. Share prior scans, recent procedures and symptoms with the team. The [PET-CT Scan](/treatments/diagnostics-and-staging/pet-ct-scan/) page explains the appointment, while [Cancer of Unknown Primary](/conditions/cancer-of-unknown-primary/) describes one situation in which imaging may help locate a source.

Contact the scan team if preparation was interrupted or you feel unwell after the tracer. Get urgent help for severe allergic-type symptoms, fainting, severe breathlessness or sudden worsening pain. Do not wait for a routine scan result if you have an emergency symptom.

Ask what the scan can and cannot show for your suspected condition, whether tissue sampling is planned, and how an active area will be distinguished from inflammation. Ask who will explain the report and what happens next.