How Doctors Diagnose Metastatic Melanoma

Medically Reviewed by Debra Jaliman, MD on March 12, 2024
3 min read

After your doctor says you have melanoma skin cancer, your first question is probably going to be: Has it spread? 

Your doctor will do tests to find out if it has moved, or “metastasized,” deeper within your skin or to other parts of your body.

There are some possible clues in the lab report your doctor got when you first got your melanoma diagnosis. If the melanoma is less than 1 millimeter thick, it’s less likely to have spread than a thicker one. The report might also mention how quickly the cancer cells are dividing and whether you have any skin ulcerations -- a break in the skin’s surface -- related to the cancer.

Even with that information, you’ll need to get some tests done to find out if it’s metastatic melanoma. You get an excision to check the lateral margins and the base. A surgical oncologist may sample nearby lymph nodes to test for spreading tumor. It may or may not need surgery, depending on the method.

It's a type of biopsy that you can get done in your doctor’s office. It checks large lymph nodes near the skin’s surface and near the melanoma to see if the cancer has spread there.

Your doctor will feel the area around your melanoma to find the lymph node or nodes, numb that spot, and use a very thin needle syringe to remove a little bit of your lymph node. It shouldn’t hurt much, and it won’t leave a scar. 

One drawback of a fine needle aspiration biopsy is that if it doesn’t collect a big enough sample, you might need to get surgery for a second biopsy.

Did your doctor say you need an operation to check your lymph nodes? In that case, you’ll probably first get an injection of a radioactive substance or dye to show the lymph nodes closest to your tumor. (Your doctor may call them your “sentinel” lymph nodes.)

The surgery is usually done in a hospital, and you can go home after it. During the procedure, the doctor makes a small cut -- about a half-inch -- and takes out one or more lymph nodes closest to your melanoma.

If those nodes contain melanoma cells, the cancer has likely spread. But if the sentinel lymph nodes show no melanoma cells, then the doctor will leave your lymph nodes alone.

Expect to wait anywhere from 2 to 3 days to 10 days or more.

Although it can be a challenge to wait for the results, the length of time depends on what the pathologist (the doctor who will check the biopsy) sees in the tissue sample.

Before, during, or after lymph node biopsy, your doctor might order one or more of the following imaging tests, too:

Ultrasound: This uses sound waves to create a picture of the inside of your body, including collections of lymph nodes. The image can help the doctor determine if melanoma has spread to a nearby lymph node before surgery, and it can help them guide a fine needle aspiration of a lymph node.

CT scan (computed tomography): This is a powerful X-ray that makes detailed pictures inside your body’s soft tissues. You lie on a table, and it rotates around you taking several pictures. If the melanoma has spread, it can show the size of a tumor. Sometimes doctors order a “contrast medium” or special dye to provide more detail on the image. Before a contrast scan, you'll get the dye injected into your vein or as a liquid to swallow. A CT scan takes longer than a typical X-ray -- usually anywhere from 15 minutes to an hour.

MRI (magnetic resonance imaging): It uses powerful magnets and radio waves to make pictures of organs and structures inside your body. For melanoma, an MRI can detect the tumor and measure its size. Like the CT scan, your doctor may order a scan with contrast to show greater detail. An MRI can take about an hour.  

PET scan (positron emission tomography): For this test, you'll get an injection of a small amount of radioactive substance (likely a sugar related to glucose) that helps “light up” quick-growing cancer cells that absorb glucose. The PET scan takes pictures and detects these radioactive areas in your body. It usually takes anywhere from 15 to 60 minutes.