A PET scan can help doctors spot cancer that has spread through the body. A doctor may request one during the melanoma diagnostic process if they suspect advanced melanoma cancer.

A PET scan is an imaging test that uses a specialty form of radioactive sugar to help doctors identify conditions such as cancer, heart disease, and neurological disorders. Doctors may recommend a PET scan during a cancer diagnostic process or to monitor cancer treatment.

A medical professional injects the radioactive sugar, called a tracer, into a person’s vein before the test. Then the cells in the body absorb it. Cells absorb different amounts of tracer sugar depending on their growth speed.

Cancer cells grow quickly and absorb more radioactive sugar than healthy cells, which causes them to show up on imaging scans.

You may also have tests such as:

  • biopsies
  • MRI
  • CT scan
  • ultrasound
  • chest X-ray

Doctors may recommend a PET scan for more advanced stages of melanoma. If the doctor believes melanoma has spread to lymph nodes or other areas of the body, a PET scan may help confirm this suspicion.

PET scans aren’t typically used during early melanoma diagnosis when no symptoms are evident or when the doctor suspects a localized tumor. This applies to skin and mucosal melanoma, a rare form of this cancer.

Mucosal melanoma forms on membranes such as those in the eyes, mouth, anus, vagina, and gastrointestinal tract.

A biopsy is the primary diagnostic test for skin and mucosal melanomas. It allows a doctor to remove a tissue sample and test it in a lab.

A biopsy is the only way to make a definitive melanoma diagnosis. A PET scan helps doctors determine if the cancer has spread to other tissues and organs beyond the membranes or skin.

A doctor may order other imaging tests during the melanoma staging phase, especially if they believe the cancer has spread.

Imaging tests for melanoma may include:

  • CT scan: A CT scan takes images of your body from multiple angles. It can help doctors see enlarged lymph nodes and tumors on organs such as the liver and lungs. Doctors may also use CT scans to guide them during needle biopsies.
  • Ultrasounds: An ultrasound uses sound waves to create images of the inside of the body. It doesn’t use radiation. It’s another test that doctors can use to look for cancer spread to lymph nodes and throughout the body. Ultrasounds are also sometimes useful for guiding needle biopsies.
  • Chest X-rays: You might have a chest X-ray if a doctor suspects melanoma has spread to your lungs.
  • MRI: An MRI uses radio waves and magnets to create detailed body images. You might have an MRI if a doctor suspects melanoma has spread to your spinal cord or brain.

A PET scan uses a low level of radiation.

Research shows that the amount of radiation used in a PET scan, and other imaging tests, is safe and there are no known risks of long-term side effects.

A PET scan is an imaging test that can help doctors see tumors inside the body. You may have one during the melanoma diagnostic process if the doctor believes the cancer has spread to other organs. A biopsy is always needed to make a definitive melanoma diagnosis.

Additional imaging tests can help detect melanoma spread and stage the cancer. For instance, a doctor may also recommend an ultrasound, MRI, or CT scan. Some imaging tests, including PET scans, use a small amount of radiation. However, this level of radiation is considered safe.