Cancer starts when cells begin to grow out of control. Cells in nearly any part of the body can become cancer, and can then spread to other areas of the body. To learn more about how cancers start and spread, see What Is Cancer?

Merkel cell carcinoma (MCC) is an uncommon type of skin cancer. It starts when cells in the skin called Merkel cells start to grow uncontrollably. This type of cancer can grow quickly and can be hard to treat if it spreads beyond the skin.

Merkel cells

Merkel cells are thought to be a type of skin neuroendocrine cell, because they share some features with nerve cells and hormone-making cells. Merkel cells are found mainly at the base of the epidermis, which is the top layer of the skin. These cells are very close to nerve endings in the skin. They help us sense light touch, which lets us do things like feel the fine details on an object’s surface.

Merkel cell carcinoma

Merkel cell carcinoma starts when Merkel cells grow out of control. Because Merkel cells are a type of neuroendocrine cell, MCC is also sometimes called neuroendocrine carcinoma of the skin. Another name for MCC is trabecular carcinoma (or trabecular cancer).

MCC is much less common than most other types of skin cancer (see below), but it’s one of the most dangerous types. It’s much more likely than common skin cancers to spread to other parts of the body if not caught early, and it can be very hard to treat if it has spread.

These cancers most often start on sun-exposed parts of the skin, such as the face (the most common site), neck, and arms. But MCC can start anywhere on the body. Merkel cell tumors usually appear as firm, pink, red, or purple lumps or bumps on the skin. They are not usually painful, but they can grow quickly and can sometimes open up as ulcers or sores (see Signs and Symptoms of Merkel Cell Carcinoma).

While nearly all MCCs start on the skin, a very small portion start in other parts of the body, such as inside the nose or esophagus.

Other types of skin cancer

Basal and squamous cell carcinomas

These are by far the most common skin cancers. They rarely spread to other parts of the body, and usually can be cured with surgery. For more information on these cancers, see Basal and Squamous Cell Skin Cancer.

Melanomas

These cancers develop from melanocytes, the pigment-making cells of the skin. Melanomas are much less common than basal and squamous cell cancers, but they are much more likely to spread and be life-threatening if not caught at an early stage. Learn more in Melanoma Skin Cancer.

Less common types of skin cancer

Other, much less common types of skin cancer include:

• Kaposi sarcoma
• Lymphoma of the skin
• Skin adnexal tumors (tumors that start in the hair follicles or skin glands)
• Various types of sarcomas

Together, these types account for less than 1% of skin cancers.

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 might do tests to find out if it’s cancer or some other skin condition. If there’s a chance the skin cancer has spread to other areas of the body, other tests might be done as well.

Medical history and physical exam

Usually the first step is for your doctor to ask about your symptoms, such as when the mark on the skin first appeared, 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, the doctor will note the size, shape, color, and texture of the area(s) in question, and if it is bleeding, oozing, or crusting. The rest of your body may be checked for spots that could be related to skin cancer.

The doctor may also feel the nearby lymph nodes, which are bean-sized collections of immune system cells under the skin in certain areas. Merkel cell carcinomas (and some other skin cancers) can spread to lymph nodes. When this happens, the lymph nodes might be felt as lumps under the skin.

If you are being seen by your primary doctor and skin cancer is suspected, you may be referred to a dermatologist (a doctor who specializes in skin diseases), who will look at the area more closely.

Along with a standard physical exam, some dermatologists use a technique called dermatoscopy (also known as dermoscopy, epiluminescence microscopy [ELM] 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 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.

Skin biopsy

If the doctor thinks that a suspicious area might be MCC (or another type of skin cancer), he or she will remove it and send it to a lab to have it 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 a local anesthetic (numbing medicine), which is injected into the area with a very small needle. You will probably feel a small prick and a little stinging as the medicine is injected, but you should not feel any pain during the biopsy.

Shave (tangential) biopsy

For this type of biopsy, the doctor shaves off the top layers of the skin with a small surgical blade. Bleeding from the biopsy site is then stopped by applying an ointment, a chemical that stops bleeding, or a small electrical current to cauterize the wound.

A shave biopsy is useful in diagnosing many types of skin diseases, especially if the doctor thinks an abnormal area is unlikely to be 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 does not go deep enough to get below the tumor. On the other hand, a deeper shave biopsy can be useful if done properly.

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 often 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 for examination, and the edges of the wound are usually stitched together.

An incisional biopsy removes only a portion of the tumor. An excisional biopsy removes the entire tumor, and is usually the preferred method of biopsy for a suspected MCC if it can be done. But this is not always possible, so other types of biopsies may be needed.

Lymph node biopsy

MCC often spreads to nearby lymph nodes early in the course of the disease, so it’s very important for the doctor to find out if these 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.

To find the sentinel lymph node (or nodes), a doctor injects a small amount of a radioactive substance into the area of the cancer. After giving the substance time to travel to the lymph node areas near the tumor, the doctor uses a special camera (and sometimes a handheld scanner) to “see” the radioactive substance where it collects in one or more sentinel lymph nodes. Once the radioactive area has been marked, the patient is taken to where the surgery will be done, and 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 turned blue. These sentinel nodes are removed and looked at with a microscope for cancer cells.

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

Needle biopsy

If a lymph node near a Merkel cell carcinoma is abnormally large, the doctor can use a needle biopsy to find out if the cancer has spread to the node. Needle biopsies are not as invasive as some other types of biopsies, but they may not always provide enough of a 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 withdraw (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, a local anesthetic is sometimes used to numb the area first. These biopsies rarely cause much discomfort and do not usually 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. For a suspicious lymph node deeper in the body, an imaging test such as ultrasound or a CT scan is often used to guide the needle into 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 has not been done (or if it did not find any cancer cells, but the doctor still suspects the cancer has spread there).

In this procedure, the doctor removes the enlarged lymph node through a small incision (cut) in the skin. This can often be done in a doctor’s office or outpatient surgical center. A local anesthetic (numbing medicine) 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 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 often used for MCC is immunohistochemistry (IHC), which 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, mitotic rate (the portion of cells that are actively dividing), and whether the tumor has invaded the tiny blood vessels or lymph vessels in the sample. These features could help determine a person’s prognosis (outlook).

Imaging tests

Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. They are often 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 determine how well treatment is working or to look for possible signs of cancer coming back (recurring) after treatment.

Computed tomography (CT) scan

The CT scan uses x-rays to make detailed, cross-sectional images of your body. Unlike a regular x-ray, CT scans can show the detail in soft tissues (such as internal organs). This test can show if any 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 within the body.

Magnetic resonance imaging (MRI) scan

MRI scans use radio waves and strong magnets instead of x-rays to create detailed images of parts of your body. This test can help tell if any lymph nodes are enlarged or if other organs have suspicious spots, which might be due to the spread of MCC. MRI scans are also very helpful in looking at the brain and 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.

For this test, you are injected with a slightly radioactive form of sugar, which collects mainly in cancer cells. A special camera is then used to create a picture of areas of radioactivity in the body.

PET/CT scan: Many centers have special machines that can do both a PET and CT scan at the same time. This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed appearance of that area on the CT scan.

Merkel cell carcinoma (MCC) usually starts on areas of skin exposed to the sun, especially the face, neck, arms, and legs, but it can occur anywhere on the body. It often first appears as a single pink, red, or purple bump that is not usually painful. Sometimes the skin on the top of the tumor might break open and bleed.

These tumors can grow quickly. They might spread as new lumps in the surrounding skin. They might also reach nearby lymph nodes (small collections of immune system cells throughout the body). Over time, the lymph nodes might grow large enough to be seen or felt as lumps under the skin (usually in the neck or under the arm).

Merkel cell carcinoma is not common, and it can look like many other, more common types of skin cancer or other skin problems when it first appears. Because of this, doctors do not usually suspect MCC at first, and the diagnosis is often made only after the tumor is biopsied.

It’s very important to have any new, growing, or changing lumps, bumps, or spots on your skin checked by a doctor as soon as possible so that the cause can be found and treated, if needed. The earlier any type of skin cancer is found, the more likely it can be treated effectively.

Skin cancer is by far the most common type of cancer in the United States, but Merkel cell carcinoma (MCC) is not common. It’s thought that about 1,500 cases of MCC are diagnosed in the United States each year.

The number of these cancers diagnosed each year has been rising quickly over the past few decades. Some of this is probably because MCC was first described only about 45 years ago. Doctors have become more aware of MCC since then, and lab tests to diagnose these cancers have become more accurate. But the rise in MCC might also be caused by increases in risk factors such as people living longer and getting more sun exposure, and more people living with weakened immune systems.

More than 9 out of 10 people diagnosed with MCC are older than age 50, and more than 2 out of 3 are older than 70.

MCC is much more common in whites than in people of other races. More than 9 out of 10 cases of MCC in the United States develop in whites.

For survival statistics, see Survival Rates for Merkel Cell Carcinoma.

Visit the American Cancer Society’s Cancer Statistics Center for more key statistics.

A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. Some risk factors, like smoking and too much sun exposure, can be changed. Others, like your age or family history, can’t be changed.

Having a risk factor for Merkel cell carcinoma (MCC), or even several risk factors, does not mean that you will get it. Most people with risk factors never get MCC, while others with this disease may have few or no known risk factors.

There are a few known risk factors for MCC.

Infection with Merkel cell polyomavirus (MCV)

Evidence of the Merkel cell polyomavirus (MCV) can be found in the cells of most Merkel cell carcinomas. But MCV is a common virus. Most people are infected with MCV at some point (often before the age of 20), but the infection doesn’t cause symptoms, and it rarely leads to MCC. Because of this, there are no recommended screening tests or treatments for MCV infection.

MCV was first discovered in 2008, so there’s still a lot that scientists don’t know about this virus. For example, it’s not clear how people are infected with MCV, exactly how it might cause MCC, or if infection with MCV is required before MCC can develop.

Ultraviolet (UV) light exposure

Exposure to ultraviolet (UV) rays is thought to be a major risk factor for most skin cancers, including MCC. UV rays damage the DNA inside skin cells. This can lead to skin cancer if this damage affects the DNA of genes that control skin cell growth.

From the sun: Sunlight is the main source of UV rays. Most MCCs start in areas of the body often exposed to the sun, such as the face, neck, and arms. People who get a lot of sun exposure are at greater risk for MCC.

UV rays make up only a very small portion of the sun’s rays, but they are the main cause of the damaging effects of the sun on the skin.

From tanning beds: Tanning beds are another source of UV rays for some people. MCC is an uncommon cancer, and no studies have looked for a link between MCC and tanning bed use. But it stands to reason that more exposure to UV rays might increase the risk.

From psoriasis treatments: Some patients with psoriasis (a long-lasting inflammatory skin disease) are given medicines called psoralens along with UV light, which is known as PUVA treatments. This can increase the risk of developing MCC.

To learn more about the effects of UV rays on the skin and what you can do to protect yourself and your loved ones, see Skin Cancer Prevention and Early Detection.

Having light-colored skin

The risk of MCC is much higher for whites than for African Americans or Hispanics. This is probably due to the protective effect of darker skin against the damaging effects of UV rays.

Being older

The risk of MCC goes up as people get older. In fact, this cancer is very rare before the age of 50. The increased risk is probably related to skin damage caused by sun exposure over time and to the fact that people’s immune systems tend to become weaker as they get older.

Being male

Men are more likely than women to develop MCC. This might be because they tend to get more sun exposure.

Having a weakened immune system

The immune system defends the body against germs such as viruses. It also seems to help the body fight some cancers of the skin and other organs. People with weakened immune systems (from certain diseases or medical treatments) are more likely to develop some types of skin cancer, including MCC.

For example, people who get organ transplants usually are given drugs that weaken their immune system to help keep them from rejecting the new organ. This increases their risk of developing MCC. People with autoimmune diseases (such as lupus) sometimes take medicines that suppress the immune system, which might increase their risk.

People infected with HIV, the virus that causes AIDS, often have weakened immune systems and are also at increased risk for MCC.

People with some types of blood cancers, such as chronic lymphocytic leukemia (CLL) or certain lymphomas, also tend to have weakened immune systems. This can be from the cancer itself or from its treatment. People with these cancers are more likely to get MCC.

MCCs in people with weakened immune systems tend to grow faster and are more likely to be life-threatening.

The risk of getting Merkel cell carcinoma (MCC) is low, and some risk factors for MCC, such as your age, gender, and skin color can’t be controlled. But there are things you can do that might help lower your risk. These might also lower your risk of getting more common types of skin cancer, or even some other types of cancer.

Limit your exposure to ultraviolet (UV) rays

The most important way to lower your risk of skin cancers (including MCC) is to limit your exposure to UV rays. Practice sun safety when you are outdoors.

Seek shade

Simply staying in the shade is one of the best ways to limit your UV exposure.

“Slip! Slop! Slap! ^®… and Wrap”

This catchphrase can help you remember some of the key steps you can take to protect yourself from UV rays. If you are going to be in the sun:

• Slip on a shirt.
• Slop on sunscreen.
• Slap on a hat.
• Wrap on sunglasses to protect the eyes and sensitive skin around them.

Avoid tanning beds and sunlamps

Many people believe the UV rays of tanning beds are harmless. This is not true. Tanning lamps give off UV rays, which can cause long-term skin damage and can contribute to skin cancer. Most skin doctors and health organizations recommend not using tanning beds and sun lamps.

Protect children from the sun

Children need special attention, since they tend to spend more time outdoors and can burn more easily. Parents and other caregivers should protect children from excess sun exposure by using the steps above. Children need to be taught about the dangers of too much sun exposure as they become more independent.

To learn more about protecting yourself in the sun…

For more on how to protect yourself and your family from UV exposure, see Skin Cancer: Prevention and Early Detection.

Avoid weakening your immune system (when possible)

Having a weakened immune system increases the risk of getting MCC, as well as other types of skin cancer.

Infection with HIV, the virus that causes AIDS, can weaken the immune system. Avoiding known risk factors for HIV infection, such as intravenous (IV) drug use and having unprotected sex with many partners, can also lower your risk of getting MCC and many other types of cancer. (For more information, see HIV Infection, AIDS, and Cancer.)

Some people need to take medicines to suppress their immune system. This includes people who have had organ transplants and some people with autoimmune diseases. People with cancer also sometimes need to take medicines such as chemotherapy that can lower their immune function. For these people, the benefit from taking these medicines will likely far outweigh the small overall increased risk of getting MCC.