Merkel cell carcinoma is a rare type of skin cancer that usually appears as a single, painless, lump on sun-exposed skin and it is typically red or violet in color. It usually appears as a flesh-colored or bluish-red nodule, often on your face, head or neck. It is considered fast-growing and can spread quickly to surrounding tissues, nearby lymph nodes, or more distant parts of the body. Merkel cell polyomavirus has been detected in about 80% of the tumors tested. It is thought that this virus can cause somatic mutations leading to MCC when the immune system is weakened. Other risk factors for developing MCC include ultraviolet radiation and being over 50 years of age. Treatment should begin early and depends on the location and size of the cancer, and the extent to which it has spread.
The most common symptom of any skin cancer, including MCC, is a change in the skin, especially a change in an existing mole or a new growth. The nodule may be skin colored or may appear in shades of red, blue or purple. Most Merkel cell carcinomas appear on the face, head or neck, but they can develop anywhere on your body, even on areas not exposed to sunlight. MCC appears as a firm, painless lump within the skin that may resemble a cyst but is fixed; i.e., cannot be moved. The lump is usually less than 2 cm (about ¾ inch) in size and can be red, pink, or blue-violet. MCC is different from other skin cancers in that it grows rapidly over a few weeks or months.
The exact underlying cause of Merkel cell carcinoma (MCC) is unknown, but several risk factors have been associated with the development of MCC. Having one or more risk factors does not mean that a person will develop MCC; most individuals with risk factors will not develop MCC. Risk factors include:
- Being over 50 years of age
- Having fair skin
- Having a history of extensive sun exposure (natural or artificial)
- Having chronic immune suppression, such as after organ transplantation or having HIV
Researchers have also found that a virus called Merkel cell polyomavirus (MCPyV) is frequently involved in the development of MCC. MCPyV is found in about 80% of tumor cells tested. This virus is thought to alter the DNA in such a way that influences tumor development. It's not clear what causes Merkel cell carcinoma. Merkel cell carcinoma begins in the Merkel cells. The virus (Merkel cell polyomavirus) lives on the skin and doesn't cause any signs and symptoms. Just how this virus causes Merkel cell carcinoma has yet to be determined. Given that the virus is very common and Merkel cell carcinoma is very rare, it's likely that other risk factors play a role in the development of this cancer. Merkel cells are found at the base of the outermost layer of your skin (epidermis). Merkel cells are connected to the nerve endings in the skin that are responsible for the sense of touch.
Factors that may increase your risk of Merkel cell carcinoma include:
- Excessive exposure to natural or artificial sunlight. Being exposed to ultraviolet light, such as the light that comes from the sun or from tanning beds, increases your risk of Merkel cell carcinoma. The majority of Merkel cell carcinomas appear on skin surfaces frequently exposed to sun.
- A weakened immune system. People with weakened immune systems — including those with HIV infection, those taking drugs that suppress the immune response or those with chronic leukemias — are more likely to develop Merkel cell carcinoma.
- History of other skin cancers. Merkel cell carcinoma is associated with the development of other skin cancers, such as basal cell or squamous cell carcinoma.
- Older age. Your risk of Merkel cell carcinoma increases as you age. This cancer is most common in people older than age 50, though it can occur at any age.
- Light skin color. Merkel cell carcinoma usually arises in people who have light-colored skin. Whites are much more likely to be affected by this skin cancer than are blacks.
Tests and procedures used to diagnose Merkel cell carcinoma include:
- Physical exam. Your doctor will examine your skin for unusual moles, freckles, pigmented spots and other growths.
- Removing a sample of suspicious skin. During a procedure called a skin biopsy, your doctor removes the tumor or a sample of the tumor from your skin. The sample is analyzed in a laboratory to look for signs of cancer.
Determining the extent:
Your doctor may use the following tests to help determine whether the cancer has spread beyond your skin:
- Sentinel node biopsy. A sentinel node biopsy is a procedure to determine whether cancer has spread to your lymph nodes. This procedure involves injecting a dye near the cancer. The dye then flows through the lymphatic system to your lymph nodes. The first lymph node that receives the dye is called the sentinel node. Your doctor removes this lymph node and looks for cancerous cells under a microscope.
- Imaging tests. Your doctor may recommend a chest X-ray and a CT scan of your chest and abdomen to help determine whether the cancer has spread to other organs.
Your doctor may also consider other imaging tests such as a positron emission tomography (PET) scan or an octreotide scan — a test that uses an injection of a radioactive tracer to check for the spread of cancer cells.
Treatments for Merkel cell carcinoma can include:
- Surgery. During surgery, your doctor removes the tumor along with a border of normal skin surrounding the tumor. If there's evidence that the cancer has spread to lymph nodes in the area of the skin tumor, those lymph nodes are removed (lymph node dissection). The surgeon most often uses a scalpel to cut away the cancer. In some cases, your doctor may use a procedure called Mohs surgery. During Mohs surgery, thin layers of tissue are methodically removed and analyzed under the microscope to see whether they contain cancer cells. If cancer is found, the surgical process is repeated until cancer cells are no longer visible in the tissue. This type of surgery takes out less normal tissue — thereby reducing scarring — but ensures a tumor-free border of skin.
- Radiation therapy. Radiation therapy involves directing high-energy beams, such as X-rays, at cancer cells. During radiation treatment, you're positioned on a table and a large machine moves around you, directing the beams to precise points on your body. Radiation therapy is sometimes used after surgery to destroy any cancer cells that remain after the tumor is removed. Radiation also may be used as the sole treatment in people who choose not to undergo surgery. Radiation can also be used to treat areas where the cancer has spread.
- Chemotherapy. Chemotherapy uses drugs to kill the cancer cells. Chemotherapy drugs can be administered through a vein in your arm or taken as a pill or both. Your doctor may recommend chemotherapy if your Merkel cell carcinoma has spread to your lymph nodes or other organs in your body, or if it has returned despite treatment.
- Mayo Clinic