What Is Merkel Cell Carcinoma?

Reviewed by: HU Medical Review Board | Last reviewed: June 2023

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

MCC is a rare form of skin cancer. About 2,000 Americans are diagnosed with MCC every year. This number has been quickly rising over the last few decades. It is unclear whether this is a true increase in this cancer or due to factors such as better diagnosis and greater awareness.2

What are the risk factors for Merkel cell carcinoma?

Most people with MCC are older than 70. Men are nearly twice as likely as women to have it. MCC is most likely to develop on sun-exposed skin after long-term sun exposure. The skin of the face, upper arms and shoulders, and lower legs and hips are the most common areas of MCC.1,3

Other risk factors for MCC include:1

  • Weakened immune system
  • Psoriasis treatment with psoralen and ultraviolet A (PUVA)
  • History of another cancer

Infection with the Merkel cell polyomavirus (MCPyV) may also play a role in MCC.1

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

  • Asymptomatic – The tumor is usually painless
  • Expanding rapidly – The tumor grows quickly
  • Immunosuppressed –A weakened immune system is a 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

What does Merkel cell carcinoma look like?

MCC can look like various things, but it is often described as a fast-growing, painless dome-shaped bump on the skin. Other common features of MCC include:4,5

  • A pearly or waxy appearance
  • A raised, irregular border
  • A blue, red, or purple color
  • Bleeding or ulceration
  • Itching or tenderness

It is hard to tell what kind of lesion it is just by looking at it, even for doctors. MCC is often not identified until the tissue sample is studied under a microscope.4,5

How is MCC diagnosed?

Your doctor will do a full skin examination. They will feel your lymph nodes to check for swelling. Swollen lymph nodes are a sign that cancer may have spread to the lymph nodes. Your doctor will perform a skin biopsy where a tissue sample is taken from the lesion. The sample is sent to a laboratory, where a pathologist examines it under a microscope.6

If the skin biopsy shows that you have MCC, you probably will need more tests to stage the cancer. Sentinel lymph node biopsy is a test to find microscopic cancer cells in a lymph node. You cannot tell by touch if microscopic cancer exists in the lymph nodes. Microscopic cancer also is too small to see with imaging tests. Imaging tests help find cancer that has spread to the lymph nodes or other body parts (distant metastasis).6

What are the treatments for MCC?

Early-stage Merkel cell carcinoma is usually treated with surgery. Your doctor will surgically cut out the tumor and a margin of healthy skin. Adjuvant radiation therapy may be used at the tumor site. Adjuvant therapy is another cancer treatment after the primary (main) treatment. This can help lower the risk that the cancer comes back.7

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 to or instead of surgery.7

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

How can I prevent MCC?

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:9

  • 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, a wide-brimmed hat, and sunglasses
  • Avoiding indoor tanning beds

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