Merkel-cell carcinoma

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at May 29, 2016
StartDiseasesMerkel-cell carcinoma

Merkel-cell carcinoma, abbreviated MCC or Merkel-cell, is also called neuroendocrine carcinoma of the skin. The cancer usually has no signs, other than a peculiar growth on the skin's surface. It is a highly aggressive cancer.

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Definition & Facts

Merkel-cell carcinoma is a rare form of skin cancer usually appearing as a small but conspicuous nodule, most often located on the head or neck. Merkel-cell carcinoma will typically grow rapidly and can quickly spread to other areas of the body. Treatment options for Merkel-cell are typically limited, and the options usually depend on if the cancer is caught early or has spread beyond the original site on the skin.

Merkel-cell carcinoma is most commonly diagnosed in older people. A weakened immune system and long-term sun exposure may increase the risk of developing Merkel-cell carcinoma.

Symptoms & Complaints

Usually, the first and only sign of Merkel-cell carcinoma is a painless nodule, or tumor, on the surface of the skin. The tumor may be neutral in color, resembling the surrounding skin, or it may appear in various shades of blue, red or purple.

Most people developing Merkel-cell carcinoma notice a nodule on the face or other areas of the head or neck. However, MCC tumors can develop anywhere on the skin anywhere on the body, even on areas not typically exposed to sunlight, such as the groin region.

Causes

Merkel-cell carcinoma begins in the Merkel cells that are located at the base of the outermost epidermis, or skin layer. Cancer is caused by changes to the DNA inside healthy cells, changes that either turn on or off actions that suppress tumor growth (tumor suppressor genes) or allow cancer cells to grow (oncogenes). Changes in multiple different genes are typically required for a cell to become cancerous. Researchers do not as of yet understand all of the DNA changes that can cause MCC; however, they have discovered mutations in the cancer cells' tumor suppressor genes.

Researchers have recently discovered a virus known as Merkel cell polyomavirus that plays a role in the majority of cases of Merkel-cell carcinoma. The polyomavirus lives on the skin, but does not cause any symptoms. Exactly how the virus causes or contributes to Merkel-cell carcinoma is not yet clear.

Given that the polyomavirus is quiet common, and Merkel-cell carcinoma is extremely rare, it is probable other risk factors have a role in Merkel-cell development. Merkel-cell carcinoma does not appear to run in families, so any DNA changes that may lead to Merkel-cell aren't likely to be passed down from parents to children. Known risk factors are long-term sun exposure and a weakened immune system.

Diagnosis & Tests

Tests used to diagnose Merkel cell-carcinoma include a physical examination where a physician will examine the skin for unusual spots, freckles, moles and growths. The doctor will perform a biopsy by removing a small segment of a suspicious area and have the sample analyzed by a laboratory to determine if the cells are cancerous. Other diagnostic tests may include: 

  • A sentinel lymph node biopsy, a procedure used to determine whether or not cancer cells have spread to the lymph nodes. The biopsy involves injecting dye near the original site of the cancer. The dye then moves throughout the lymphatic system to all lymph nodes in the body. The first lymph node to receive the dye is termed the sentinel node. The physician will surgically remove the sentinel lymph node and exam it for malignant cells under a microscope.
  • Imaging tests, such as CT scans and X-rays of the chest and abdominal area, are performed to determine if the cancer has metastasized, or spread, to other organs. CT scans, short for computerized tomography, produce cross-sectional and three-dimensional images of the body, with the aid of a computer. The doctor may also perform other types of imaging tests if positive results are found. 

Treatment & Therapy

Treatments for Merkel-cell carcinoma include:

  • Surgery to remove the skin tumor and a border of noncancerous skin surrounding the tumor. 
  • A second form of surgery, called lymph node dissection where the lymph nodes are removed, will be performed if there is evidence the cancer has spread to those nodes in the area of the tumor.
  • The physician may use a procedure referred to as Mohs surgery, where thin layers of tissue are methodically removed and analyzed. If cancer is discovered, the process is repeated until cancer cells are no longer found in the tissue. Mohs surgery is less invasive because it does not remove as much normal tissue. 
  • Radiation therapy that directs high-energy beams, like X-rays, to target cancer cells. Radiation therapy is often used as a precaution after surgery to destroy any remaining cancer cells. However, radiation can be used as the main form of treatment in individuals who don't want to undergo surgery. Radiation is also used to treat areas the cancer has spread to. 
  • Chemotherapy is the use of drugs to kill the cancer cells. Chemotherapy drugs can be administered orally, intravenously, or both. Chemotherapy is usually warranted if Merkel-cell carcinoma has spread to other areas of the body, or returned after initial treatment.

Prevention & Prophylaxis

The risk of getting MCC is very low. Some of the risk factors for Merkel cell-can’t be controlled, such as age, skin color and gender. However, there are things that can be done to help lower your risk. Most importantly, practice sun safety when outdoors and limit exposure to UV rays.

This includes staying in the shade and wearing a shirt, hat, sunglasses and sunscreen with a minimum of 30 SPF. Tanning beds should also be avoided, as these too produce UV rays and can cause skin damage that can contribute to cancer. A weakened immune system also increases the risk of Merkel cell-carcinoma, so it is important to maintain one's overall health and eat a healthy diet, get enough sleep, and partake in regular exercise.