Tests for Merkel Cell Carcinoma

Most skin cancers, including Merkel cell carcinoma (MCC), are brought to a doctor’s attention because a person has noticed a change in an area of skin.

If you have an abnormal area that might be skin cancer, your doctor will examine it and order tests to find out if it’s cancer or some other skin problem. If Merkel cell carcinoma is diagnosed, you will probably need other tests as well to learn more about it, including if it has spread.

Medical history and physical exam

First, you will be asked about your symptoms, such as when you first noticed the change on your skin, if it has changed in size or how it looks, and if it has been painful, itchy, or bleeding. You might also be asked about your possible risk factors (including sun exposure and immune system problems) and if you or anyone in your family has had skin cancer.

During the physical exam, the area(s) in question will be looked at. 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 cells in the body, will also be checked. Merkel cell carcinoma (and some other skin cancers) can sometimes spread to the lymph nodes. When this happens, the lymph nodes swell and might be felt as lumps under the skin.

Referral to a skin specialist

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

Along with doing a standard physical exam, the dermatologist might use a technique called dermoscopy (also called dermatoscopy, epiluminescence microscopy [ELM], or surface microscopy) to look at spots on the skin more closely. 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 on the skin with this instrument. The doctor may take digital photos of the spot, too.

Skin biopsy

If the doctor thinks that a suspicious area might be Merkel cell cancer or another type of skin cancer, the area (or part of it) will be removed. This is called a skin biopsy. The biopsy sample is then sent to a lab, here it's tested and looked at with a microscope.

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

Skin biopsies usually are done after a local anesthetic (numbing medicine) 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.)

Deep shave (tangential) biopsy

This biopsy procedure, also known as saucerization, shaves off the top layers of the skin with a small surgical blade. Any bleeding is then stopped by putting either an ointment or a chemical that stops bleeding on it, or by 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 isn’t likely to be a serious skin cancer such as Merkel cell carcinoma or melanoma. If this type of biopsy is used, it’s important that the biopsy blade goes deep enough to get below the tumor.

Punch biopsy

For a punch biopsy, a tool that looks like a tiny round cookie cutter is used 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 then 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 make an elliptical or circular cut through the full thickness of skin. A wedge or sliver of skin is removed, and the edges of the cut 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 Merkel cell cancer, if it can be done.

Lymph node biopsy

Merkel cell cancer often spreads to nearby lymph nodes, so it’s very important to find out if the 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 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 or surgical biopsy is more likely to be done. This is often done with the help of an imaging test (see below), such as an ultrasound, CT scan, or fluoroscopy (continuous x-ray).

Sentinel lymph node biopsy (SLNB)

A sentinel lymph node biopsy is a surgical procedure that is used to find the lymph nodes that are likely to be the first place Merkel cell cancer would spread to. These lymph nodes are called sentinel nodes.

To find the sentinel lymph node (or nodes), a small amount of a radioactive substance is injected into the area of the tumor. After giving the substance time to travel to the lymph node areas near the tumor, a special camera is used to see if it collects in one or more sentinel lymph nodes.

Once the radioactive area has been marked, the patient is taken for surgery, and usually a blue dye is injected in the same place the radioactive substance was injected. A small incision is then made in the marked area, and the lymph nodes are then checked to find which one(s) became radioactive and/or turned blue. These sentinel nodes are removed by the surgeon and sent to a pathology lab, where they are examined to see if Merkel cell cancer is present.

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

Needle biopsy

If a lymph node near a Merkel cell cancer 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 less invasive 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 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 sometimes feel it well enough to guide the needle into it. If not, or 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 can't be done for some reason. 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 may be done in a doctor’s office or in an 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 Merkel cell cancer (or other types of cancer). The biopsy samples are usually 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 in the skin biopsy sample, 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) and treatment options.

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 Merkel cell cancer 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 using more energy (which might be a sign of cancer), rather than just showing if areas look abnormal based on their size or shape.

PET/CT or PET/MRI scan: Often a PET scan is combined with a CT scan or MRI scan, using special machines that can do both at the same time. This lets the doctor compare areas of higher cell activity on the PET scan with the more detailed pictures of that area on the CT or MRI scan. This type of imaging scan is often preferred in patients with MCC.

Blood tests

Blood tests aren’t used to diagnose Merkel cell carcinoma, but some tests may be done before, during, or after treatment, especially for more advanced MCCs.

For example, tests of blood cell counts and blood chemistry levels are often done in people with MCC to see how well their bone marrow (where new blood cells are made), liver, and kidneys are working before and during treatment.

People with Merkel cell cancer might also have their blood tested for antibodies to the Merkel cell polyomavirus (MCV) around the time they start treatment. For those who have antibodies to MCV, the levels should fall over time if treatment is working. On the other hand, rising antibody levels after treatment can be a sign that the cancer has come back (recurred).