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Merkel cell carcinoma (MCC) is a rare and aggressive form of skin cancer. A thorough diagnosis and appropriate treatment options are essential to cure this disease. Fred Hutch Cancer Center offers comprehensive treatment from a team of experts who specialize in MCC.
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What Is Merkel Cell Carcinoma?
Merkel cells are cells normally in the bottom layer of your epidermis — the outermost layer of the two main layers of your skin (the dermis is the deeper layer). They function mainly as touch receptors and relay touch-related information, such as texture and pressure, to your brain.
Scientists studying these cells believe that MCC doesn’t actually start with normal Merkel cells. Instead, it’s more likely that the stem cells in the skin that normally produce Merkel cells can also, in some cases, develop into Merkel cell carcinoma. More MCC facts:
- MCC usually appears as a lump that has grown rapidly on sun-exposed areas of the head, neck, arms or legs, but it can also appear in areas typically protected from the sun.
- MCC often metastasizes (spreads) to other parts of the body. Even small tumors may metastasize.
- When the disease spreads, it often spreads to nearby lymph nodes and may also spread to the liver, bone, lungs and brain.
Merkel cell carcinoma usually is caused in part by an extremely common — and typically harmless — virus that was discovered in 2008, the Merkel cell polyomavirus. Another cause is extensive exposure to sunlight, especially in people with fair skin. This exposure can occur at any time, including childhood. About 80% of MCC cases are caused by the Merkel cell polyomavirus, and about 20% are caused by extensive sun damage.
People who have significant, prolonged suppression of their immune system (such as after a kidney or heart transplant or due to infection with human immunodeficiency virus, HIV) are at high risk of MCC, but over 90% of MCC patients have no known problem with their immune system.
Merkel cell carcinoma is diagnosed with a skin biopsy, which means samples of cells are taken from the tumor and examined under a microscope by a pathologist. Common types of biopsy include a punch biopsy (a small cylinder of tissue is taken) or a shave biopsy (part of the top of the abnormal tissue is removed with a scalpel).
Special stains are used to distinguish this cancer from other forms of cancer, such as small cell lung cancer, lymphoma, melanoma or other sun-induced skin cancers, and from benign (noncancerous) cysts.