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Melanoma: Tests After Diagnosis

Once you’re diagnosed with melanoma, you will need more tests. These tests help your healthcare providers learn more about your cancer. They can help show if the cancer has grown into nearby areas or spread to other parts of the body. The test results help your providers decide how to treat the cancer. If you have any questions about these or other tests, talk with your healthcare team. You may need 1 or more of these tests:

  • Sentinel lymph node biopsy

  • Fine needle aspiration (FNA) biopsy

  • CT scan

  • MRI

  • PET scan

  • Blood tests

  • Chest X-ray

Sentinel lymph node biopsy

You may need a sentinel lymph node biopsy if you have a thick melanoma or one with other features that make it more likely to have spread. This procedure removes nearby lymph nodes to check for cancer cells. It’s done because melanoma often spreads first to the lymph nodes.

In a group of lymph nodes, cancer is most likely to go to 1 or 2 lymph nodes first. These lymph nodes are called sentinel lymph nodes. During the procedure, a surgeon removes 1 or more sentinel lymph nodes. Any nodes removed are then looked at for cancer cells. If no cancer is found, the melanoma is unlikely to have spread beyond this point. The other lymph nodes in the group can be left in place. Results of a sentinel lymph node biopsy help your provider figure out what treatment you may need.

During a sentinel node biopsy:

  • The process starts with lymph node mapping. This is a way to find out which lymph node nearest to the melanoma is the sentinel node. To fine the sentinel lymph node (or nodes), the provider may use a radioactive tracer, a blue dye, or both. The provider injects a small amount of radioactive tracer into your skin near the melanoma site. It takes about an hour for the tracer to follow the same path as a melanoma cell would to the nearest lymph node.

  • The provider uses a special device that detects radioactivity a lot like a Geiger counter does. This helps to show where the cancer cells are most likely to go. The provider also may inject a blue dye that travels to the lymph nodes. The lymph node that shows up with radioactivity or with the blue dye is called the sentinel lymph node. 

  • The provider makes a small incision to remove this lymph node (or nodes).

  • Right after removing the lymph node, your provider may do a wide local excision. This is a surgery to remove more tissue around the melanoma. This can help prevent melanoma from coming back (recurring).

  • The sentinel lymph node is examined in a lab for cancer cells.

  • If it doesn't have melanoma cells, you may not need more tests. The provider will leave the other lymph nodes in place.

  • If the removed sentinel lymph node (or nodes) has melanoma cells, your provider may decide to remove all the lymph nodes in that region if there are non-sentinel lymph nodes that may have cancer present. This is called lymph node dissection. You might also need imaging tests such as CT scans, MRI, or a PET scan. You may also need blood tests.

FNA biopsy

If your healthcare provider thinks the cancer has spread to a certain lymph node or organ, you may have an FNA biopsy. This is to confirm if cancer is present. You may first get a local numbing medicine. The test rarely causes much discomfort and leaves little scarring. The provider uses a syringe with a small needle to remove a small sample of tissue from the node or organ. The provider may use imaging tools, such as a CT scan or ultrasound, during the biopsy. This is to help guide the needle to the right place. The tissue sample is examined in a lab for cancer cells.

CT scan

This test helps your provider see where the melanoma is located and if it has spread to other parts of your body. It's helpful for finding melanoma in the chest, abdomen, and pelvis.

A CT scan uses a series of X-rays and a computer to create detailed images of the inside of the body. During the test, you lie still on a table as it slowly slides through the center of the CT scanner. The scanner directs a beam of X-rays at your body. A CT scan is painless. You may be asked to hold your breath one or more times during the scan. You may need to drink a dye (contrast medium) or get it in an IV (intravenous) injection before the test.

The IV dye allows your provider to better see lymph nodes and other tissues. Some people have a temporary warm feeling (flushing) just after the injection. The ingested dye will gradually pass through your system and exit through your bowel movements. Tell your provider if you have ever had a reaction to contrast material in the past, such as hives or trouble breathing. Tell your provider if you have these reactions during the test.


This test is helpful in looking at your brain and spinal cord. MRI may also be used if the results of an X-ray or CT scan aren’t clear. MRIs use radio waves, magnets, and a computer to make detailed images of the inside of the body.

For this test, you lie still on a table as it passes through a tubelike scanner. If you're not comfortable in small spaces, you may be given medicine before the test to help you relax. The scanner directs a beam of radio waves at the area of the body being examined. You may need more than 1 set of images. Each may take 2 to 15 minutes. This test is painless. It may last an hour or more. The machine is loud during the test. You can ask for earplugs or headphones with music. A type of contrast dye might be given before the MRI.

PET scan

A PET scan can examine your entire body. For this test, you either swallow or are injected with a mildly radioactive substance (tracer), usually a form of sugar. The PET scan will show where in your body the sugar is being used the most. This helps find active cells that are dividing quickly, such as cancer cells.

You’ll lie still on a table that is pushed into the PET scanner. It will rotate around you and take pictures. Other than the injection, a PET scan is painless and noninvasive. Some people are sensitive to the substance and may have nausea, a headache, or vomiting. You may have a PET/CT scan. This machine can do both a PET and CT scan at the same time, so areas that show up on the PET scan can be compared with the more detailed image of the CT scan. 

Blood tests

Your provider may tell you to get a lactate dehydrogenase (LDH) test before you have treatment. LDH is an enzyme in the blood. Sometimes LDH blood levels are high when many cancer cells are present or when the liver has been damaged by cancer. This test can be helpful in showing if cancer has spread.

Your provider may want you to have other blood tests to check blood cell counts and blood chemistry before or during treatment. It can show how well the bone marrow, liver, and kidneys are doing.

Chest X-ray

A chest X-ray is done to see if there are any changes in your lungs. This may show that the melanoma has spread. An X-ray uses a small amount of radiation to make an image of organs and bones inside the body. The test can also spot enlarged lymph nodes in your chest area. This test takes a few minutes and causes no pain.

Working with your healthcare provider

Your provider will talk with you about which tests you’ll have. Make sure to prepare for the tests as instructed. Ask questions and talk about any concerns you have.

Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Online Medical Reviewer: Susan K. Dempsey-Walls APRN
Online Medical Reviewer: Todd Gersten MD
Date Last Reviewed: 8/1/2023
© 2024 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare provider's instructions.