Merkel Cell Carcinoma

Table of Contents

Merkel cell carcinoma (MCC) is a rare type of skin cancer. It is sometimes called neuroendocrine carcinoma of the skin or trabecular cancer. MCC forms when the body’s Merkel cells grow out of control. These cells can be found in the top layer of the skin and are close to the nerve endings.

MCC usually develops in areas where the skin is exposed to the sun. These areas include the head, neck, arms, and legs. This cancer can grow quickly and metastasize (spread) to other parts of the body. MCC often spreads first to nearby lymph nodes. It may then spread to lymph nodes or the skin in other areas. It may even spread to the lungs, brain, bone, or other organs.

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Risk Factors

Anything that increases a person’s risk of getting a disease is called a risk factor. Having one or even many risk factors does not mean that a person will get the disease. Risk factors for Merkel cell carcinoma include the following:

  • Being exposed to a lot of natural sunlight
  • Being exposed to artificial sunlight, such as from tanning beds
  • Being exposed to psoralen (a drug to make your skin more sensitive to ultraviolet A light) and ultraviolet A (PUVA) therapy for psoriasis
  • Having an immune system weakened by disease, such as chronic lymphocytic leukemia or HIV infection
  • Taking drugs that weaken the immune system
  • History of cancer
  • Having a lighter skin color
  • Being male or over the age of 50

Signs & Symptoms

A sign of MCC is the presence of a lump or bump on the skin that is red or violet in color. These tumors can be firm and dome-shaped or raised. They are usually painless, but they can grow fast and turn into ulcers or sores.

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Diagnosis & Treatment Planning


To diagnose MCC, your doctor may perform the following tests and procedures to examine the skin.

  • Physical exam: A doctor will check your body for general signs of health and signs of disease.
  • Health history: A doctor may ask about your health habits, past illnesses, and any previous treatments.
  • Full-body skin exam: A doctor or nurse will check the skin for any unusual areas. They will look for any bumps or spots that may have an unusual color, size, shape, or texture. They will also check the size, shape, and texture of your lymph nodes.
  • Skin biopsy: Some of your skin cells or skin tissue will be removed and observed under a microscope to check for signs of cancer.



After confirming a MCC diagnosis, the doctor needs to know the stage (extent) of the disease to plan the best treatment. Staging is used to find out whether the cancer has spread, and if so, to which areas of the body.

The following tests may be performed to confirm the stage of the cancer.

CT scan: An x-ray machine takes detailed images of areas inside the body. You may be asked to swallow a type of dye, or a dye will be injected into your vein. This helps the tissues and organs show up clearly on the scan. CT scans are usually done on the chest, abdomen, head, and neck.

PET scan: A type of radioactive glucose (sugar) is injected into a vein. Unhealthy cancer cells take in more sugar than healthy cells. This helps show the areas where the cancer has spread.

Lymph node biopsy: A doctor will remove a piece of the lymph node and examine it under a microscope. This may require surgery to get a large enough sample or if the lymph node is in a location that is more difficult to get to. Sometimes the entire lymph node may need to be removed for an accurate diagnosis. There are several types of lymph node biopsies for MCC:

  • Sentinel lymph node biopsy: The sentinel node is the first lymph node that gets lymphatic drainage from the MCC tumor. It is removed during surgery and observed under a microscope to check for cancer cells.
  • Lymph node dissection: Some, or all, of the lymph nodes are removed during surgery. They are then observed under a microscope to check for cancer cells.
  • Core needle biopsy: A sample of tissue is removed from a lymph node using a wide needle.
  • Fine-needle aspiration biopsy: A sample of tissue is removed from a lymph node using a thin needle.

There are 5 different stages of MCC: 

Unhealthy Merkel cells are found in the top layer of the skin. These cells can become cancerous and spread to nearby tissue. 

Unhealthy Merkel cells form into a tumor that is less than 2 centimeters wide. Stage I MCC is divided into 2 stages:

  • Stage IA – No cancer is found when the lymph nodes are checked under a microscope.
  • Stage IB – No lymph nodes are swollen when checked during a physical exam.

Stage II MCC is divided into 2 stages:

  • Stage IIA – The tumor is larger than 2 centimeters. No cancer is found when the lymph nodes are checked under a microscope.
  • Stage IIB – The tumor has spread to nearby connective tissue, cartilage, muscle, or bone.

Stage III MCC is divided into 2 stages:

Stage IIIA

  • The tumor is any size and may have spread to nearby connective tissue, cartilage, or bone. The lymph node is not swollen, but cancer is found in the lymph node when observed under a microscope.
  • Or, the lymph node is swollen during the physical exam. When the lymph node is removed and observed under a microscope, cancer is present.

Stage IIIB

  • The tumor is any size and may have spread to nearby connective tissue, muscle, cartilage, or bone. The lymph node is swollen, and cancer is found in the lymph node.
  • Or, cancer is found in a lymph vessel. The lymph vessel is between the primary tumor and the lymph nodes. Cancer also may have spread to the lymph nodes.
  • The cancer has spread to the skin that is farther away from the primary tumor.
  • Or, the cancer has spread to other areas of the body, such as the liver, lung, bone, or brain.

Treatment Options

Different types of treatment are available for patients with MCC. Some treatments are standard (what is currently used), and some are being tested in clinical trials. Clinical trials are research studies that test new treatments or learn how to use existing treatments better. Talk with your doctor to see if a clinical trial is right for you. Clinical trials may be available before, during, or after standard treatment has begun.

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Your doctor will recommend treatment options based on the stage of your cancer, your overall health, and your treatment preferences. When the cancer has spread, the location and extent of MCC is also important to consider. 

Talk with your doctor about developing a treatment plan that covers managing your cancer in the short-term and long-term. Consider your treatment options carefully. Ask questions if you do not understand something about your treatment or the medical terms your doctor is using. Write down questions before your visits and take notes as your doctor talks so that you can remember what was said. You may want to bring a friend or family member to take notes for you during appointments. It is okay to get a second opinion to discuss your diagnosis or treatment options.

Treatment options for MCC include the following:

One or more of the following surgical procedures may be used to treat MCC:

Wide local excision

The cancer and the tissue around it is cut from the skin. A sentinel lymph node biopsy may be done during the excision. If there is cancer in the lymph nodes, a lymph node dissection may take place.

Lymph node dissection

  • A regional lymph node dissection removes some of the lymph nodes in the tumor area.
  • A radical lymph node dissection removes most or all the lymph nodes in the tumor area. This procedure is also called a lymphadenectomy.

Mohs surgery

The cancer is removed a layer at a time. Each layer is checked under the microscope to see if all the cancer is removed. A few layers may need to be removed to make sure all the cancer is gone.

Radiation therapy uses high-energy rays to kill cancer cells or keep them from growing. This treatment is usually painless and lasts only a few minutes.

External radiation therapy is most often used to treat MCC that has recurred, spread to the lymph nodes, or spread to distant parts of the body. It can also be used to treat any cells left behind after surgery or when surgery isn’t an option. 

Immunotherapy is a treatment that uses the body’s natural defenses (the immune system) to fight cancer. Substances made by the body or made in a laboratory are used to boost, direct, or restore the immune system.

Immune checkpoint inhibitors are a type of immunotherapy that helps boost the immune system’s response against cancer cells. These drugs block immune system cells that have substances that act as checkpoints to keep them from attacking other healthy cells in the body. Blocking these checkpoints can boost the immune response against cancer cells. This treatment is often used for Merkel cell carcinoma that has spread.

Chemotherapy is a systemic (whole body) treatment. This treatment uses drugs to destroy cancer cells or stop them from growing.

Chemotherapy drugs may be given by mouth or through an IV in the vein depending on the type and stage of the cancer. Chemotherapy is often used to treat MCC that has spread to other organs.

Coping With Side Effects

Before you begin treatment, it is helpful to learn about the side effects so that you know what to expect. When you know more, you can work with your health care team to manage your quality of life during and after treatment.

Common side effects of radiation therapy for MCC include:

  • Sunburn-like skin issues
  • Changes in skin color
  • Hair loss near the treatment area
  • Fatigue
  • Nausea (if the abdomen is included in the radiation treatment area)

Common side effects of immunotherapy for MCC include:

  • Fatigue
  • Cough
  • Nausea
  • Itching
  • Joint pain
  • Loss of appetite
  • Diarrhea or constipation

Common side effects of chemotherapy for MCC may include:

  • Hair loss
  • Mouth sores
  • Loss of appetite
  • Nausea and vomiting
  • Diarrhea or constipation
  • Increased chance of infections (due to low white blood cell counts)
  • Easy bruising or bleeding (due to low blood platelet counts)
  • Fatigue (due to low red blood cell counts)

There are many medications available to address side effects from cancer treatment. Everyone reacts differently to treatment and experiences side effects differently. Speak with your health care team about any side effects you experience and ways to minimize and treat them. If side effects persist and are not easy to manage, your doctor may discuss options such as lowering the dose of your treatment. You also may want to consult a palliative and supportive care specialist to help manage symptoms from cancer treatment.

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