Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare type of skin cancer. Merkel cells are thought to be a skin neuroendocrine cell because they share some features with nerve cells and hormone-making cells. When they’re healthy, neuroendocrine cells receive information from the nervous system and release hormones in response. The Merkel cells are very close to nerve endings in the skin. 

MCC starts when the Merkel cells in the skin start to grow out of control. MCC tends to grow quickly and can spread to other parts of the body. About 3,000 people are diagnosed with Merkel cell carcinoma in the United States each year. Merkel cell carcinoma is also sometimes called neuroendocrine carcinoma of the skin or trabecular carcinoma (or trabecular cancer). 

Types & Stages

Unlike most other skin cancer, Merkel cell carcinoma doesn’t have distinct “types.” Instead, after a diagnosis, your doctor will try to figure out if it has spread, and if so, how far. This process is called staging. The stage of a cancer describes how much cancer is in your body. It helps determine how serious the cancer is and how best to treat it. Your doctor will also use a cancer's stage when talking about survival statistics.

The earliest stage Merkel cell cancers are called stage 0 (or carcinoma in situ, meaning it’s only on the outer layer of the skin), and then range from stages I through IV. As a rule, the lower the number, the less the cancer has spread. A higher number, like stage IV, means cancer has spread more. And within a stage, an earlier letter means a lower stage. Although each person’s cancer experience is unique, cancers with similar stages tend to have a similar outlook and are often treated in much the same way.

The two main types of staging for MCC are:

• The clinical stage, which is based on the results of physical exams, biopsies and any imaging tests that have been done. The clinical stage can be used to help plan treatment.
   
• After the skin biopsy to confirm the diagnosis, if surgery is done (to remove more of the area around the skin tumor, as well as to check nearby lymph nodes for cancer), the pathological stage (also called the surgical stage) can be determined.

Staging for Merkel cell carcinoma can be complex, so ask your doctor to explain it to you in a way you understand.

Signs & Symptoms

Merkel cell carcinoma usually starts on areas of skin that are exposed to the sun, especially the face, neck, arms and legs, but it can occur anywhere on the body.

• The first sign of Merkel cell carcinoma is often a single pink-red or purple shiny bump that usually doesn't hurt. Sometimes the skin on the top of the tumor breaks open and bleeds.
   
• These tumors tend to grow quickly. They might spread as new lumps in the nearby 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 rare, 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 might not 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 easier it’s likely to be to treat it.

Diagnosis

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'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.
   
• 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 types of biopsies include:
   
  • 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.
     
  • Punch biopsy. For this, a tool that looks like a tiny round cookie cutter is used to remove a deeper sample of skin. Your 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. 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 your 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.
     
• Imaging tests. Your doctor might suggest imaging tests. These might include a computerized tomography scan, also called a CT scan, a positron emission tomography scan, also called a PET scan, or an MRI (magnetic resonance imaging).  

Treatment

Because some sort of surgery is often needed to diagnose Merkel cell cancer or find out if it has spread, the diagnosis and treatment often occur together. The most common surgeries for MCC include:  

• Wide excision. When Merkel cell carcinoma is diagnosed by a skin biopsy, more of the tumor site will most likely need to be cut out (excised) to help make sure the cancer has been removed completely. This surgery might cure MCC if it hasn’t spread beyond where it started. This fairly minor operation will cure most thin melanomas. Local anesthesia is injected into the area to numb it before the excision. The site of the tumor is then cut out, along with a small amount of normal skin around the edges (called the margins). The wound is usually stitched back together afterward. The removed sample is then viewed with a microscope to make sure that no cancer cells were left behind.
   
• Mohs surgery. Also known as Mohs micrographic surgery or MMS, this is sometimes used when the goal is to save as much healthy skin as possible, such as with cancers on the face or ears. This type of surgery is done by a specially trained dermatologist or surgeon. In this procedure, the skin (including the tumor) is removed in very thin layers. Each layer is quickly frozen and looked at with a microscope. If cancer cells are seen, the doctor removes another layer of skin. This is repeated until a layer shows no signs of cancer. This is a slow process, often taking several hours, but it means that more normal skin near the tumor can be saved, which can help the area look better after surgery.
   
• Amputation. In rare cases where the cancer is on a finger or toe and has grown deep into the skin, part or all of that digit might need to be removed (amputated).
   
• Lymph node dissection. Merkel cell skin cancer often spreads to nearby lymph nodes. If cancer is found in nearby lymph nodes, a lymph node dissection may be done. In this operation, your surgeon removes all the lymph nodes near the primary tumor. For instance, if the MCC is found on an arm, the surgeon would remove the underarm (axillary) lymph nodes on that side of the body. These nodes are where cancer cells would be most likely to go first. This type of surgery is done in an operating room, where you’re given medicines to put you into a deep sleep (general anesthesia). 

Causes & Risk Factors

These are some known risk factors for Merkel cell carcinoma:

• Ultraviolet (UV) light exposure. This can be from sunlight, tanning beds and other UV lights.
   
• Having light-colored skin. The risk of Merkel cell cancer is much higher for white people, accounting for nearly all (more than 9 out of 10) MCCs. This is probably because darker skin has a protective effect against the damaging effects of UV rays.
   
• Age. The risk of Merkel cell carcinoma goes up as people get older. In fact, this cancer is very rare in people under the age of 50. About 8 out of 10 people with MCC are over age 70.
   
• Gender. Men are about twice as likely as women to develop Merkel cell carcinoma. The reason for this isn’t clear, but it might be because men tend to get more sun exposure. 
   
• From psoriasis treatments. Some people with psoriasis (a long-lasting inflammatory skin disease) are given medicines called psoralens along with UV light treatments, known as PUVA treatments. 
   
• Merkel cell polyomavirus (MCV) infection. MCV is a common virus that’s found in the cancer cells of about 8 out of 10 people with Merkel cell carcinoma. Most people are infected with it at some point (often as children). 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.
   
• Having a weakened immune system. People with weakened immune systems (from certain diseases or medical treatments) are more likely to develop some types of cancer, including Merkel cell carcinoma. For example, people who get organ transplants, people with HIV, the virus that causes AIDS, and people with some types of blood cancers, such as chronic lymphocytic leukemia (CLL) or certain lymphomas, tend to have weakened immune systems. MCCs in people with weakened immune systems tend to grow faster and are more likely to be life-threatening.
   
• Long-term exposure to arsenic. Some studies have suggested that long-term exposure to high levels of arsenic might increase the risk of Merkel cell cancer.

Screening

With skin self-exams and skin checks by a health care professional like a dermatologist, Merkel cell cancers can often be found early. When skin cancers are found early, they are likely to be easier to treat.