What is Merkel Cell Carcinoma?

Reviewed by: HU Medical Review Board | Last reviewed: May 2017. | Last updated: April 2019

Merkel cells are in the top layer of skin, close to the nerve endings for the sense of touch.1 Merkel cell carcinoma (MCC) develops when Merkel cells begin to grow out of control.

MCC is a rare form of skin cancer. It affects about 1 in 126,500 people in the United States.2 The number of new cases seems to be rising. It is not clear whether this is a true increase in this cancer or due to factors such as better diagnosis and greater awareness.

What are risk factors for Merkel cell carcinoma?

The median age at diagnosis is 65 years. MCC is more likely in white than black persons, and slightly more common in men than women.1 It is most likely to develop on sun-exposed skin after long-term sun exposure.3 The face, shoulders, and upper arms are the most common locations for MCC.4

Other risk factors for MCC include:

  • Weakened immune system (eg, after organ transplantation, chronic blood cancer, or HIV infection)
  • Psoriasis treatment with psoralen and ultraviolet A (PUVA)
  • History of another cancer

Infection with the Merkel cell polymavirus may play a role in MCC. Evidence of this virus is found in up to 80% of MCC.5

The memory aid AEIOU may help you to remember typical risk factors and characteristics of MCC:1

  • Asymptomatic: The tumor is usually painless
  • Expanding rapidly: The tumor grows quickly
  • Immunosuppressed: Weakened immune system is an important risk factor for MCC
  • Older than 50: Older age is another risk factor for MCC
  • UV-exposed skin: Most tumors appear on sun-exposed skin

How is Merkel cell carcinoma diagnosed?

Your doctor will do a full skin examination. She or he will feel your lymph nodes to see if they are swollen or enlarged.5 Enlarged lymph nodes are a sign that cancer may have spread to the lymph nodes. Your doctor will perform a skin biopsy, which is when a sample of tissue is taken from the lesion. The sample is sent to a laboratory, where a pathologist examines it under a microscope.

If the skin biopsy shows that you have MCC, you probably will need additional tests to stage the cancer.3Sentinel lymph node biopsy is a test to find microscopic cancer cells in a lymph node. You cannot tell by feel if there is microscopic cancer in the lymph nodes. Microscopic cancer also is too small to see with imaging tests.3Imaging tests produce pictures of your body. They help to find cancer that has spread to the lymph nodes or other parts of the body (distant metastasis).

What are the recurrence and survival rates for Merkel cell carcinoma?

MCC is an aggressive cancer.5 At the time of diagnosis, more than one-third of patients have cancer in the lymph nodes.6 Up to 12% have distant metastasis at diagnosis.6

Recurrence is common, occurring in 25% to 30% of cases.3 Recurrence rates are higher when the cancer has started to spread. In one study, the median time-to-recurrence was 9 months.1 Nearly all (91%) recurrences occurred within 2 years of diagnosis.1

Because there are so few people with MCC, survival rates are hard to estimate. Local MCC is when the cancer has not spread beyond the skin. The 5- and 10-year survival rates for local MCC are above 70%.2,4 For cancer that has spread to the lymph nodes, the 5- and 10-year survival rates are 54% and 48%.2,4 For distant metastatic MCC, the 10-year survival rate is 20%.4

What does Merkel cell carcinoma look like?

Merkel Cell Carcinoma

A large red merkel cell carcinoma on a person's eyelid.

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A typical MCC lesion is a painless red or purplish dome-shaped lump that grows quickly.5 The lesion may feel firm. It may be shiny and have visible blood vessels. MCC also can be a rough, hard patch on the skin.7

It is hard to tell what kind of lesion it is is just by looking at it—even for doctors. MCC is often not identified until the tissue sample is studied under a microscope.3

What are the treatments for Merkel cell carcinoma?

Early-stage Merkel cell carcinoma is usually treated with surgery.3 Your doctor will excise (cut out) the tumor, along with a margin of healthy skin. Adjuvant radiation therapy may be used at the tumor site. Adjuvant therapy is an additional cancer treatment that is given after the primary (main) treatment. Adjuvant therapy can help lower the risk that the cancer comes back.

If cancer cells are found in your lymph nodes, the lymph nodes probably will be removed. The affected lymph nodes may be treated with radiation therapy in addition or as an alternative to surgery.

For cancer that has spread to distant parts of the body, treatment options include:3,8

How can I prevent Merkel cell carcinoma?

You can lower your risk of Merkel cell carcinoma by reducing your exposure to ultraviolet (UV) light. The risk of MCC has been linked to long-term sun exposure. There are many ways to reduce your UV exposure, including:

  • Using a broad spectrum sunscreen with a sun protection factor (SPF) 15 or higher.
  • Seeking shade between 10 am and 2 pm.
  • Wearing long sleeves, long pants, wide-brimmed hat, and sunglasses.
  • Avoiding indoor tanning beds.

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