Many different types of tests are used to help diagnose cancer, determine the cancer’s stage, monitor how well treatment is working, and watch for a cancer recurrence (return of the cancer). Imaging tests (or scans) are ways to create pictures of the organs and tissues inside the body. Different types of scans are often used at different points in a person’s cancer diagnosis, treatment, and recovery.
A positron emission tomography (PET) scan  is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive sugar substance is injected into the patient’s body. This sugar substance is taken up by cells that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.
Sometimes, a PET scan is combined with a computed tomography (CT) scan, called a PET-CT scan , to provide a more complete image than either test alone. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors.
ASCO recommends that PET or PET-CT scans not be used to watch for a cancer recurrence in patients with no symptoms of a recurrence who have finished treatment that was intended to eliminate the cancer.
What this means for patients
PET and PET-CT scans can be very helpful to diagnose or find out the stage of cancer. However, research has not shown that they lengthen patients’ lives when used to search for a cancer recurrence. In addition, if these tests indicate a person has a cancer recurrence when they actually do not (called a false positive), sometimes invasive, unnecessary follow-up testing needs to be done. This can be difficult for patients physically, emotionally, and financially. After treatment for cancer, talk with your doctor about the goals of each upcoming scan and how you will be best monitored for a possible recurrence as part of your survivorship follow-up care.
Questions to ask your doctor
- What is my schedule for follow-up care once cancer treatment is complete?
- Will I need any testing, and if so, which tests and how often?
- What are the risks, benefits, and costs of these tests?
- What symptoms and signs should I report to you right away? What should I report at my regular follow-up visits?
For More Information
Guides to Cancer