What Is Merkel Cell Carcinoma?

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Merkel cell carcinoma (MCC) is a rare, but fast-growing type of skin cancer that begins in the top layer of the skin, near nerve endings. MCC typically presents as a discolored bump on areas that are regularly exposed to the sun, such as the face, head, or neck.

This article will discuss the causes, symptoms, treatment, and outlook for Merkel cell carcinoma.

Merkel Cell Carcinoma

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Merkel Cell Carcinoma Symptoms

Typically, the first sign of MCC is the appearance of a red or purple lump or bump on the skin. They may be firm and dome-shaped, and usually doesn't cause any pain.

Unfortunately, this symptom can be mistaken for a number of other skin blemishes, so it's best to get the lump examined as soon as possible.

Some things an MCC tumor can mimic include:

  • Bites
  • Pimples
  • Sores
  • Cysts
  • Styes
  • Hair follicles

One sign that the lump or bump might be an MCC tumor is if it grows very quickly.

Warning Signs of Merkel Cell Carcinoma

The Skin Cancer Foundation offers this “AEIOU” guide to help spot Merkel cell carcinoma:

  • "A" stands for asymptomatic. The lump isn’t painful or tender.
  • "E" stands for expanding. The lesion expands very quickly.
  • "I" stands for immunocompromised. You are more at risk for Merkel cell carcinoma if you have a weak immune system.
  • "O" stands for older. You have a higher risk if you’re older.
  • "U" stands for UV-exposed. The lumps usually show up on areas of the skin that have been exposed to ultraviolet (UV) light.

Causes

Researchers don’t know what exactly causes MCC, but it is thought that sun exposure and a weakened immune system are the two biggest risk factors.

The main risk factors include:

  • Sun exposure: Most Merkel cell carcinomas develop on areas frequently exposed to the sun.
  • Exposure to artificial light: The use of tanning devices or ultraviolet (UV) light therapy for psoriasis has been linked to this cancer.
  • Weak immune system: People with conditions that affect the immune system, such as human immunodeficiency virus (HIV) or leukemia, are at a greater risk. Immunosuppressant medications may also weaken the immune system and increase the chances of developing MCC.
  • Fair skin: People with light, or fair, skin are more likely to develop MCC.
  • Age: This cancer is more common in people older than age 50.
  • Biological sex: Men are more likely to develop MCC than women.
  • History of skin cancer. Other skin cancers, such as melanoma, basal cell carcinoma, or squamous cell carcinoma, are associated with an increased risk for Merkel cell carcinoma.

Researchers have recently discovered that a common virus, called Merkel cell polyomavirus, plays a role in the development of many Merkel cell carcinoma cases. This virus lives on the skin and doesn’t cause symptoms. Because the virus is common and Merkel cell carcinoma is rare, experts say these other factors must contribute to the development of this cancer.

Merkel Cell Polyomavirus

Merkel cell polyomavirus, which was discovered in 2008, lives in the skin of most people without developing into cancer. Between 60% and 80% of Americans carry this virus. Researchers are still unsure how or why the virus causes Merkel cell carcinoma in some people.

Diagnosis

To diagnose MCC, a physician will first perform a skin exam to look at the lesion or lump in question.

If the lump looks suspicious, a skin biopsy will be done to make a diagnosis. During this procedure, tissue from the lump is removed and sent to a lab for analysis. A lymph node biopsy may also be needed to see if the cancer has spread.

Imaging tests can also help determine if MCC has spread in the body, such as:

Challenges in Diagnosis 

Because Merkel cell carcinomas can mimic other skin appearances, it has a high risk of being misdiagnosed. About 56% of Merkel cell carcinomas are thought to be noncancerous when first examined. They can easily be mistaken for cysts or infected hair follicles.

Merkel cell carcinomas are also hard to detect when they form in places like the mouth, nasal cavity, or throat. In one study, about 14% of Merkel cell carcinomas were first identified in the lymph nodes, without any tumor being detected.

Treatment is much more successful if MCCs are caught early, which can be difficult when suspicious lesions are ignored or misdiagnosed. Be sure to meet with your healthcare provider as soon as possible if you suspect lump or skin appearance may be cancerous.

Look Out For Signs

To help catch MCC in its early stages, be sure to:

  • Examine your skin for changes every month.
  • See a dermatologist once a year.
  • Regularly follow up with a physician if you’ve had a Merkel cell carcinoma or other type of skin cancer in the past.

Treatment

Treatment for Merkel cell carcinoma will depend on the patient's overall health and how advanced the cancer is. The most common treatment options for MCC include surgery, radiation, immunotherapy, chemotherapy, or some combination of these.

Surgery

Surgery is often used to remove cancerous lesions.

A primary surgical method is wide local excision, which involves cutting the cancer from the skin along with some of the tissue around it.

Another type of procedure, called Moh’s micrographic surgery, involves removing the tumor layer by layer. Each layer of tissue is assessed under a microscope, so less skin has to be removed than in traditional procedures. This method is preferred for facial lesions to preserve the skin on the face.

Individuals may also need some or all of their lymph nodes in the area removed, depending on how advanced the disease is.

Radiation

Radiation therapy uses high energy particles to kill cancer cells. It’s often used along with surgery as a treatment option for people with MCC.

Immunotherapy

Immunotherapy medications help your immune system fight cancer. Some common immunotherapies used for Merkel cell carcinoma are:

  • Bavencio (avelumab)
  • Opdivo (nivolumab)
  • Keytruda (pembrolizumab)

Chemotherapy

Chemotherapy involves using drugs to kill cancer cells in the body. Chemotherapy can sometimes be used for Merkel cell carcinomas that have advanced.

Finding the Right Specialist

Because Merkel cell carcinoma is so rare, it’s important to find a healthcare professional or specialist who has experience in treating this form of cancer. Look for specialists who are familiar with this disease.

Prognosis

A patient's outlook will depend on the stage of cancer, the chosen treatment method, and other factors.

Only about 3,000 new cases of Merkel cell carcinoma are diagnosed in the United States each year. The five-year survival rate across all stages of Merkel cell carcinoma is 63%.

However, statistics don't dictate specific cases. As researchers continue to study new treatments for this uncommon cancer, survival rates are expected to improve.

Coping

Learning you have cancer can be scary and overwhelming for you and your loved ones. If you are diagnosed with Merkel cell carcinoma, surround yourself with a strong support team to help you tackle the disease.

Following these tips can also help you take control of your disease:

  • Protect your skin from the sun.
  • Avoid indoor tanning.
  • Perform frequent skin exams.
  • Call your physician if you notice any new growths or lesions.

Connecting with others who have a similar experience can help you cope. Look for online or in-person supports groups by visiting Merkelcell.org.

A Word From Verywell

Being diagnosed with a rare cancer like Merkel cell carcinoma can be overwhelming. It’s important to be your own advocate and work closely with a specialized medical team. Not all physicians will have experience with this disease, so search for a specialist who can help you treat MCC, and get second opinions if needed. Catching and treating MCC early can improve your outlook significantly.

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9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. National Cancer Institute. Merkel cell carcinoma treatment. Updated June 25, 2021.

  2. American Academy of Dermatology Association. Skin cancer types: Merkel cell carcinoma signs & symptoms.

  3. Skin Cancer Foundation. Merkel cell carcinoma: overview. Updated February 2020.

  4. Skin Cancer Foundation. Merkel cell carcinoma warning signs. Updated January 2021.

  5. Cleveland Clinic. Merkel cell carcinoma. Updated January 11, 2019.

  6. Skin Cancer Foundation. Merkel cell carcinoma risk factors. Updated April 2019.

  7. Harms, P.W., Harms, K.L., Moore, P.S. et al. The biology and treatment of Merkel cell carcinoma: current understanding and research prioritiesNat Rev Clin Oncol. 2018;15(12):763-776. doi:10.1038/s41571-018-0103-2

  8. American Academy of Dermatology Association. Skin cancer types: Merkel cell carcinoma causes.

  9. American Cancer Society. Survival rates for merkel cell carcinoma. Updated January 21, 2021.