Merck Manual

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Merkel Cell Carcinoma

(Neuroendocrine Skin Carcinoma; Primary Small Cell Skin Carcinoma; Trabecular Cell Carcinoma; APUDoma of the Skin; Anaplastic Skin Cancer)


Gregory L. Wells

, MD,

  • Idaho College of Osteopathic Medicine
  • Ada West Dermatology and Dermatopathology

Last full review/revision May 2019| Content last modified May 2019
Click here for the Professional Version

Merkel cell carcinoma is a rare, rapidly spreading skin cancer that tends to affect older white people.

Merkel cells are normal cells in the epidermis (the outer layer of the skin). These cells mostly function as touch receptors and they produce certain hormones. Merkel cell carcinoma arises from uncontrolled growth of cells in the skin that share some characteristics with normal Merkel cells.

Merkel cell carcinoma is diagnosed at an average age of 75. Merkel call carcinoma also affects younger people whose immune system is weakened. Sun exposure increases the risk, as does having another cancer. The Merkel cell polyomavirus may be a contributory factor. This cancer commonly spreads to the lymph nodes.


The cancer is typically a firm, shiny, flesh-colored or bluish red bump. Cancers tend to grow rapidly without causing pain or tenderness. Although Merkel cell carcinoma can affect any part of the skin, it is most common on skin that has been chronically exposed to sunlight (for example, the face and arms).


  • Biopsy

A biopsy is done to confirm the diagnosis of Merkel cell carcinoma. During this procedure, a small piece of skin is removed and examined under a microscope.

In most people, the cancer has already spread by the time the diagnosis has been made, so the prognosis of Merkel cell carcinoma is poor.


Because Merkel cell carcinoma can be caused by sun exposure, people can help prevent this cancer by doing the following:

  • Avoiding the sun: For example, seeking shade, minimizing outdoor activities between 10 AM and 4 PM (when the sun’s rays are strongest), and avoiding sunbathing and the use of tanning beds

  • Wearing protective clothing: For example, long-sleeved shirts, pants, and broad-brimmed hats

  • Using sunscreen: At least sun protection factor (SPF) 30 with UVA and UVB protection used as directed and reapplied every 2 hours and after swimming or sweating but not used to prolong sun exposure


  • Surgical removal of the tumor

  • Usually radiation therapy and removal of lymph nodes

  • Sometimes chemotherapy

Treatment of Merkel cell carcinoma usually involves surgery to remove the tumor, often followed by radiation therapy, removal or biopsy of lymph nodes, or both.

If cancer has spread or returns, chemotherapy may be recommended.

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