Merkel cell carcinoma (MCC) is also called neuroendocrine carcinoma of the skin. It’s a type of skin cancer that occurs when cells in the skin, known as Merkel cells, grow uncontrollably. The cancer usually presents as a single reddish or purple lump on a part of the skin that is often exposed to sunlight, such as the face, neck, or arms.

Although skin cancer is the most common type of cancer in the United States, Merkel cell carcinoma is considered rare. Only 1,500 people in the United States are diagnosed with MCC each year. The majority of people diagnosed with this type of cancer are white and over the age of 70.

Merkel cell carcinoma is different from other types of skin cancer because of the type of cells involved. Merkel cell carcinoma starts in the Merkel cells. By comparison, basal cell carcinoma, the most common type of skin cancer, occurs in the basal cells of the skin. Melanoma develops from skin cells known as melanocytes.

After receiving a cancer diagnosis, your doctor will run tests to find out if the cancer has spread to other parts of your body. This is referred to as staging. Staging is important for determining what types of treatment are needed.

In general, a higher number stage means the further a cancer has spread. There are five main stages in MCC (stages 0 to 4):

  • stage 0: the cancer is only in the epidermis and hasn’t spread to the lymph nodes
  • stage 1: the cancer is less than 2 centimeters (cm) across and hasn’t grown into the lymph nodes
  • stage 2: the cancer is more than 2 cm across and hasn’t spread to the lymph nodes
  • stage 3: the cancer has grown into lymph nodes as well as nearby tissues
  • stage 4: the cancer has spread to nearby tissues, the lymph nodes, and distant sites, such as the lungs, bones, or brain

The main symptom of Merkel cell carcinoma is the appearance of a single lump or nodule on the skin. The lump is typically:

  • red or violet in color
  • firm to the touch
  • fast-growing
  • painless

The nodule can form anywhere on the body, but most often appears on areas regularly exposed to sunlight, such as the:

  • face
  • neck
  • arms

If the cancer spreads to the lymph nodes, the nodes may grow large enough to be seen as lumps under the skin.

Merkel cell carcinoma can look like many other types of skin cancer at first, so a definitive diagnosis usually isn’t made until after a biopsy. Other types of skin cancers often present with:

  • abnormal nodules
  • raised bumps
  • irregularly shaped moles
  • red, pink, brown, or blue rough patches of skin

If you have a lump or patch on your skin, it doesn’t necessarily mean you have cancer, but you should see a dermatologist for a complete examination.

Merkel cell carcinoma originates in cells at the bottom of the epidermis, known as the Merkel cells. The epidermis is the outer layer of the skin. Merkel cells are connected to nerve endings that give us our sense of touch.

Merkel cell carcinoma occurs when something goes wrong within these cells and causes them to grow uncontrollably. Researchers haven’t yet pinpointed the exact cause. Scientists have recently found that a virus known as the Merkel cell polyomavirus might play a role.

Other known risk factors include:

  • being older than 50 years old
  • excessive sun exposure
  • using tanning beds
  • having light-colored skin
  • having a compromised immune system, including people with HIV or chronic leukemia, and people taking immunosuppressive drugs

Merkel cell carcinoma may be detected during a physical exam by your doctor or dermatologist. Your doctor will check for lumps, lesions, or irregularly shaped moles. They may also ask you for a detailed medical history, history of sun exposure, and if anyone in your family has had skin cancer.

If your doctor finds anything abnormal, they may perform a skin biopsy to check for cancer. During a skin biopsy, a tiny amount of the lump is removed and viewed under a microscope.

If the biopsy is positive for Merkel cell carcinoma, your doctor will run additional tests to determine the stage and extent of the cancer. These tests may include:

Depending on the stage of the cancer and your overall health, your treatment options may include one or more of the following:

  • surgery to remove the tumor and any affected lymph nodes
  • radiation treatment, which directs high energy beams at the cancer cells (this treatment is often used following surgery to kill any remaining cancer cells)
  • chemotherapy drugs (these are often recommended if the cancer has spread to the lymph nodes or other parts of the body, or if it has returned even after surgery and radiation)

Your doctors will discuss the benefits of each option, as well as the possible risks and side effects.

Merkel cell carcinoma is considered an aggressive type of cancer. This means that it can rapidly spread (metastasize) to other parts of the body, including the lymph nodes, brain, and lungs. Metastatic cancer is difficult to treat and has a low survival rate.

Merkel call carcinoma is uncommon, so it’s difficult to estimate an accurate survival rate. The survival rate tells you what percentage of people with the same type and stage of cancer are still alive after a defined period of time after diagnosis.

According to the American Cancer Society, the overall five-year survival rate for MCC is about 60 percent. This means that about 60 percent of people diagnosed with MCC will still be alive after five years.

Your outlook depends on how early the cancer is diagnosed. The following five-year relative survival rates are based on stages 1 through 4 of diagnosis:

  • stage 1A: 80 percent
  • stage 1B: 60 percent
  • stage 2A: 60 percent
  • stage 2B: 50 percent
  • stage 3A: 45 percent
  • stage 3B: 25 percent
  • stage 4: 20 percent

People with weakened immune systems or who are very old tend to have a worse outlook.

While you can’t completely prevent Merkel cell carcinoma, you can reduce your risk of getting it by:

  • avoiding tanning beds
  • staying out of the sun during peak hours (between 10AM and 4PM)
  • wearing sunglasses and a hat with UV protection when you go out in the sun
  • using sunscreen often

You can help detect potential problems early on by performing a skin self-examination once a month. During a self-examination, you check all over your skin to look for any abnormal lumps, or any spots that are new or changing in size, shape, or color.

If you notice anything abnormal, visit your doctor or dermatologist for an evaluation. Detecting cancer in its early stages increases the likelihood that you’ll be able to successfully treat it.