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Tests for Merkel Cell Carcinoma

Most skin cancers, including Merkel cell carcinoma (MCC), are brought to a doctor’s attention because of signs or symptoms a person is having.

If you have an abnormal area that might be skin cancer, your doctor will examine it and do tests to find out if it’s cancer or some other skin problem. If MCC is diagnosed and there’s a chance it has spread to other parts of your body, other tests will be needed.

Medical history and physical exam

The first step is for your provider to ask about your symptoms, such as when you first noticed the change on your skin, if it has changed in size or appearance, and if it has been painful, itchy, or bleeding. You might also be asked about your possible risk factors for skin cancer (including sun exposure and immune system problems) and if you or anyone in your family has had skin cancer.

During the physical exam, your provider will note the size, shape, color, and texture of the area(s) in question, and if it's bleeding, oozing, or crusting. The rest of your body will also be checked for spots that could be related to skin cancer.

Nearby lymph nodes , which are bean-sized collections of immune system cells under the skin will also be closely checked. MCCs (and some other skin cancers) can spread to lymph nodes. When this happens, the lymph nodes swell and might be felt as lumps under the skin.

Referral to a specialist

If you're first seen by your primary doctor and skin cancer is suspected, you may be referred to a dermatologist. This is a doctor who specializes in skin diseases. This doctor will look at the changed area more closely.

Along with a standard physical exam, some dermatologists use a technique called dermatoscopy (also called dermoscopy, epiluminescence microscopy, or surface microscopy) to see spots on the skin more clearly. The doctor uses a dermatoscope, which is a special magnifying lens and light source that's held near the skin. Sometimes a thin layer of alcohol or oil is used with this instrument. The doctor may take a digital photo of the spot, too.

Skin biopsy

If the doctor thinks that a suspicious area might be MCC (or another type of skin cancer), a tiny piece of it (called a sample) will be removed and sent to a lab. There, it's tested and looked at with a microscope. This is called a skin biopsy.

There are different ways to do a skin biopsy. The doctor will choose one based on the suspected type of skin cancer, where it is on your body, its size, and other factors. Different methods can result in different scars, so ask your doctor about possible scarring before the biopsy is done.

Skin biopsies are done using local anesthetic (numbing medicine), which is injected into the area with a very small needle. You'll probably feel a small prick and a little stinging as the medicine goes in, but you shouldn't feel any pain during the biopsy.

(For animated views of some of these procedures, see Skin Biopsy and Treatment Procedures.)

Shave (tangential) biopsy

To do this biopsy, the doctor shaves off the top layers of the skin with a small surgical blade. Any bleeding is then stopped by putting on either an ointment, a chemical that stops bleeding, or using a small electrical current to seal (cauterize) the wound.

A shave biopsy is useful in diagnosing many types of skin diseases, especially if the doctor thinks an abnormal area is not likely a serious skin cancer such as MCC or melanoma. A thin shave biopsy is generally not used if the doctor strongly suspects MCC (or melanoma), because the biopsy often doesn't go deep enough to get below the tumor.

Punch biopsy

For a punch biopsy, the doctor uses a tool that looks like a tiny round cookie cutter to remove a deeper sample of skin. The doctor rotates the punch biopsy tool on the skin until it cuts through all the layers of the skin. The sample is removed and the edges of the biopsy site are stitched together.

Incisional and excisional biopsies

To examine a tumor that might have grown into deeper layers of the skin, the doctor may use an incisional or excisional biopsy. For these types of biopsies, a surgical knife is used to cut through the full thickness of skin. A wedge or sliver of skin is removed, and the edges of the wound are stitched together.

  • An incisional biopsy removes only part of the tumor.
  • An excisional biopsy removes the entire tumor, and is usually preferred for a suspected MCC if it can be done.

Lymph node biopsy

MCC often spreads to nearby lymph nodes early in the course of the disease, so it’s very important to find out if lymph nodes contain cancer cells. If MCC has already been diagnosed on the skin, nearby lymph nodes will usually be biopsied to see if the cancer has spread to them.

The type of biopsy used depends on how likely it is that the cancer has reached the nearby lymph nodes:

  • If the nearby lymph nodes feel normal on physical exams and look normal on imaging tests, a sentinel lymph node biopsy is likely to be done.
  • If exams or imaging tests suggest that nearby lymph nodes might contain cancer (for example, if the nodes are larger than normal), then a needle biopsy is more likely to be done.

Sentinel lymph node biopsy (SLNB)

A sentinel lymph node biopsy can be used to find the lymph nodes that are likely to be the first place the MCC would go if it has spread. These lymph nodes are called sentinel nodes.

For more on this test and what the results could mean, see Surgery for Merkel Cell Carcinoma.

Needle biopsy

If a lymph node near an MCC tumor is abnormally large, the doctor can use a needle biopsy to find out if the cancer has spread to that node. Needle biopsies are easier than some other types of biopsies, but they may not always take out enough of a tissue sample to find cancer cells.

There are 2 main types of needle biopsies.

  • In a fine needle aspiration (FNA) biopsy, the doctor uses a syringe with a very thin, hollow needle (thinner than the ones used for blood tests) to pull out (aspirate) cells and small pieces of tissue.
  • In a core biopsy, a larger needle is used to remove one or more small cylinders (cores) of tissue. Core biopsies remove larger samples than FNA biopsies.

With either type of biopsy, numbing medicine (a local anesthetic) is sometimes used to numb the area first. These biopsies rarely cause much discomfort and usually don't leave a scar.

If the lymph node is just under the skin, the doctor can often feel it well enough to guide the needle into it. If the lymph node is deeper in the body, an imaging test, like an ultrasound or CT scan, is often used to guide the needle into the right place.

Surgical (excisional) lymph node biopsy

This type of biopsy might be done if a lymph node’s size suggests the cancer has spread there but a needle biopsy of the node hasn't been done. An excisional biopsy might also be used if a needle biopsy didn't find any cancer cells, but the doctor still suspects the cancer has spread there.

In this type of biopsy, the doctor takes out the enlarged lymph node through a small cut (incision) in the skin. This can often be done in a doctor’s office or outpatient surgical center. Numbing medicine (local anesthetic) is generally used if the lymph node is near the surface of the body, but a person may need to be sedated or even asleep (using general anesthesia) if the lymph node is deeper in the body.

Lab tests of biopsy samples

All biopsy samples will be sent to a lab, where a pathologist (a doctor who is specially trained to diagnose disease) will look at them under a microscope and do tests for MCC (or other types of cancer). Often, skin samples are sent to a dermatopathologist, a doctor who has special training in looking at skin samples.

If the doctor can’t tell for sure if the sample contains MCC just by looking at it, special lab tests may be done on the cells to try to confirm the diagnosis. One of the tests commonly used for MCC is called immunohistochemistry (IHC). It looks for certain proteins on the cancer cells, such as CK-20.

If MCC is found, the pathologist will also look at certain important features such as the tumor thickness, the portion of cells that are actively dividing (mitotic rate), and whether the tumor has invaded the tiny blood vessels or lymph vessels in the sample. These features could help determine a person’s outlook (prognosis).

Imaging tests

Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. They can be used to see if MCC has spread to lymph nodes or to other organs in the body.

Imaging tests can also be done to help see how well treatment is working or to look for possible signs of cancer coming back (recurring) after treatment.

Computed tomography (CT) scan

CT scans use x-rays to make detailed, cross-sectional images of your body. Unlike a regular x-ray, CT scans can show details in soft tissues (such as internal organs). This test can show if lymph nodes are enlarged or if other organs have suspicious spots, which might be from the spread of MCC.

CT-guided needle biopsy: CT scans can also be used to help guide a biopsy needle into a suspicious area deep inside the body.

Magnetic resonance imaging (MRI)

MRIs use radio waves and strong magnets instead of x-rays to create detailed images of the inside of your body. This test is very helpful in looking for cancer that has spread to the brain and/or spinal cord.

Positron emission tomography (PET) scan

A PET scan can help show if the cancer has spread to lymph nodes or other parts of the body. This test looks for areas where cells are growing quickly (which might be a sign of cancer), rather than just showing if areas look abnormal based on their size or shape.

PET/CT scan: Often a PET scan is combined with a CT scan using a special machine that can do both at the same time. This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed pictures of that area on the CT scan. This is the type of imaging scan most preferred in patients with MCC.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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National Comprehensive Cancer Network, Clinical Practice Guidelines in Oncology (NCCN Guidelines®), Merkel Cell Carcinoma, Version 2.2018 -- June 15, 2018. Accessed at on August 8, 2018.


Last Revised: October 9, 2018

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