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Merkel Cell Carcinoma

Merkel cell carcinoma, also called neuroendocrine carcinoma of the skin or trabecular cancer, is a very rare type of skin cancer that forms when Merkel cells grow out of control. Merkel cells are found in the top layer of the skin. These cells are very close to the nerve endings that receive the sensation of touch. Merkel cell carcinoma starts most often in areas of skin exposed to the sun, especially the head and neck, as well as the arms, legs, and trunk

Merkel cell carcinoma tends to grow quickly and to metastasize (spread) at an early stage. It usually spreads first to nearby lymph nodes and then may spread to lymph nodes or skin in distant parts of the body, lungs, brain, bones, or other organs.

Signs and Symptoms

Merkel cell carcinoma usually appears as a single painless lump on sun-exposed skin.  
This and other changes in the skin may be caused by Merkel cell carcinoma. Other conditions may cause the same symptoms so a doctor should be consulted if changes in the skin are seen. Merkel cell carcinoma usually appears on sun-exposed skin as a single lump that is: 

  • Fast-growing.
  • Painless.
  • Firm and dome-shaped or raised.
  • Red or violet in color. 

Risk Factors

Sun exposure and having a weak immune system can affect the risk of developing Merkel cell carcinoma. These include the following:

  • Being exposed to a lot of natural sunlight.
  • Being exposed to artificial sunlight, such as from tanning beds or psoralen 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 make the immune system less active, such as after an organ transplant.
    Having a history of other types of cancer.
  • Being older than 50 years, male, or white.   

Diagnosis 

The following tests and procedures may be used to diagnose Merkel cell carcinoma: 

  • Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient's health habits and past illnesses and treatments will also be taken.
  • Full-body skin exam: A doctor or nurse checks the skin for bumps or spots that look abnormal in color, size, shape, or texture. The size, shape, and texture of the lymph nodes will also be checked.
  • Biopsy: The removal of cells or tissues so they can be viewed under a microscope by a pathologist to check for signs of cancer.

Staging Procedures

After Merkel cell carcinoma has been diagnosed, tests are done to find out if cancer cells have spread to other parts of the body. Cancer spreads in the body in three ways:

  1. Through tissue. Cancer invades the surrounding normal tissue.
  2. Through the lymph system. Cancer invades the lymph system and travels through the lymph vessels to other places in the body.
  3. Through the blood. Cancer invades the veins and capillaries and travels through the blood to other places in the body.

When cancer cells break away from the primary (original) tumor and travel through the lymph or blood to other places in the body, another (secondary) tumor may form. This process is called metastasis. The secondary (metastatic) tumor is the same type of cancer as the primary tumor. For example, if breast cancer spreads to the bones, the cancer cells in the bones are actually breast cancer cells. The disease is metastatic breast cancer, not bone cancer.

The system for determining the severity of the cancer is called staging. The information gathered from the staging process determines the stage of the disease, which is important in determining the most effective treatment. The following tests and procedures are used in staging Merkel cell carcinoma : 

  • CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body, taken from different angles. The pictures are made by a computer linked to an x-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. A CT scan of the chest and abdomen may be used to check for primary small cell lung cancer, or to find Merkel cell carcinoma that has spread. A CT scan of the head and neck may also be used to find Merkel cell carcinoma that has spread to the lymph nodes. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography.
  • MRI (magnetic resonance imaging): A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body. This procedure is also called nuclear magnetic resonance imaging (NMRI).
  • PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do.
  • Octreotide scan: A type of radionuclide scan used to find carcinomas and other types of tumors. A small amount of radioactive octreotide (a hormone that attaches to carcinoid tumors) is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to the tumor and a special camera that detects radioactivity is used to show where the tumor cells are in the body.
  • Sentinel lymph node biopsy: The removal of the sentinel lymph node during surgery. The sentinel lymph node is the first lymph node to receive lymphatic drainage from a tumor. It is the first lymph node the cancer is likely to spread to from the tumor. A radioactive substance and/or blue dye is injected near the tumor. The substance or dye flows through the lymph ducts to the lymph nodes. The first lymph node to receive the substance or dye is removed. A pathologist views the tissue under a microscope to look for cancer cells. If cancer cells are not found, it may not be necessary to remove more lymph nodes.
  • Lymph node dissection: A surgical procedure in which the lymph nodes are removed and a sample of tissue is checked under a microscope for signs of cancer. For a regional lymph node dissection, some of the lymph nodes in the tumor area are removed. For a radical lymph node dissection, most or all of the lymph nodes in the tumor area are removed. This procedure is also called lymphadenectomy. 

Staging System

The following stages are used for Merkel cell carcinoma:

Sarcoma Sizes



Stage 0 (carcinoma in situ)
 
In stage 0, the tumor is a group of abnormal cells that remain in the place where they first formed and have not spread. These abnormal cells may become cancer and spread to lymph nodes or distant parts of the body.
 
Stage IA
 
In stage IA, the tumor is 2 centimeters or smaller at its widest point and no cancer is found when the lymph nodes are checked under a microscope.
 
Stage IB
 
In stage IB, the tumor is 2 centimeters or smaller at its widest point and no swollen lymph nodes are found by a physical exam or imaging tests.
 
Stage IIA
 
In stage IIA, the tumor is larger than 2 centimeters and no cancer is found when the lymph nodes are checked under a microscope.
 
Stage IIB
 
In stage IIB, the tumor is larger than 2 centimeters and no swollen lymph nodes are found by a physical exam or imaging tests.
 
Stage IIC
 
In stage IIC, the tumor may be any size and has spread to nearby bone, muscle, connective tissue, or cartilage. It has not spread to lymph nodes or distant parts of the body.
 
Stage IIIA
 
In stage IIIA, the tumor may be any size and may have spread to nearby bone, muscle, connective tissue, or cartilage. Cancer is found in the lymph nodes when they are checked under a microscope.
 
Stage IIIB
 
In stage IIIB, the tumor may be any size and may have spread to nearby bone, muscle, connective tissue, or cartilage. Cancer has spread to the lymph nodes near the tumor and is found by a physical exam or imaging test. The lymph nodes are removed and cancer is found in the lymph nodes when they are checked under a microscope. There may also be a second tumor, which is either: 

  • Between the primary tumor and nearby lymph nodes; or
  • Farther away from the center of the body than the primary tumor is.

 Stage IV
 
In stage IV, the tumor may be any size and has spread to distant parts of the body, such as the liver, lung, bone, or brain.

Recurrent Merkel Cell Carcinoma

Recurrent Merkel cell carcinoma is cancer that has recurred (come back) after it has been treated. The cancer may come back in the skin, lymph nodes, or other parts of the body. It is common for Merkel cell carcinoma to recur.

Treatment

Surgery

One or more of the following surgical procedures may be used to treat Merkel cell carcinoma: 

  • Wide local excision: The cancer is cut from the skin along with some of the tissue around it. A sentinel lymph node biopsy may be done during the wide local excision procedure. If there is cancer in the lymph nodes, a lymph node dissection also may be done.
  • Lymph node dissection: A surgical procedure in which the lymph nodes are removed and a sample of tissue is checked under a microscope for signs of cancer. For a regional lymph node dissection, some of the lymph nodes in the tumor area are removed; for a radical lymph node dissection, most or all of the lymph nodes in the tumor area are removed. This procedure is also called lymphadenectomy.

Even if the doctor removes all the cancer that can be seen at the time of the surgery, some patients may be given chemotherapy or radiation therapy after surgery to kill any cancer cells that are left. Treatment given after the surgery, to lower the risk that the cancer will come back, is called adjuvant therapy.

Radiation Therapy

Radiation therapy is a cancer treatment that uses high-energy x-rays or other types of radiation to kill cancer cells. There are two types of radiation therapy. External radiation therapy uses a machine outside the body to send radiation toward the cancer. Internal radiation therapy uses a radioactive substance sealed in needles, seeds, wires, or catheters that are placed directly into or near the cancer. The way the radiation therapy is given depends on the type and stage of the cancer being treated. 

Chemotherapy

Chemotherapy is a cancer treatment that uses drugs to stop the growth of cancer cells, either by killing the cells or by stopping the cells from dividing. When chemotherapy is taken by mouth or injected into a vein or muscle, the drugs enter the bloodstream and can reach cancer cells throughout the body (systemic chemotherapy). When chemotherapy is placed directly into the cerebrospinal fluid, an organ, or a body cavity such as the abdomen, the drugs mainly affect cancer cells in those areas (regional chemotherapy). The way the chemotherapy is given depends on the type and stage of the cancer being treated.

Treatment Options by Stage

Note: A link to a list of current clinical trials is included for each treatment section. For some types or stages of cancer, there may not be any trials listed. Check with your doctor for clinical trials that are not listed here but may be right for you.

Stage I and Stage II Merkel Cell Carcinoma

Stage III Merkel Cell Carcinoma

Stage IV Merkel Cell Carcinoma

Treatment of stage IV Merkel cell carcinoma may include the following as palliative treatment to relieve symptoms and improve quality of life:

  • Chemotherapy.
  • Surgery.
  • Radiation therapy.
  • A clinical trial of a new treatment.

Recurrent Merkel Cell Carcinoma 

  • Wide local excision to remove a larger area of tissue than was removed in earlier surgery. A lymph node dissection may also be done.
  • Radiation therapy after surgery.
  • Chemotherapy.
  • Radiation therapy and/or surgery as palliative treatment to relieve symptoms and improve quality of life.
  • Clinical trial for patients with recurrent neuroendocrine carcinoma of the skin

Credits: Portions of the text on this page were reproduced, modified or adapted from either works in the public domain, freely licensed media file repositories, or from other UCSF websites. Here the sources used were: the websites of the National Cancer Institute (NCI) - Merkel Cell Carcinoma
(cancer.gov), the originator of the content.

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