Merkel cell carcinoma, also called neuroendocrine cancer of the skin, is a rare type of skin cancer that affects about 2,500 people in the United States each year. Like other types of skin cancer, that number is growing.
With detection in early stages and appropriate treatment, Merkel cell carcinoma can often be cured. More advanced tumors or tumors that spread may require more complex treatment strategies, but these tumors can still be cured.
Merkel cell tumors usually occur on sun-exposed skin, such as the head, neck, and extremities (arms, hands, feet, and legs). But they can also happen on other parts of the body that are not usually exposed to sun. Their shape and color are less distinctive than other skin cancers, and they often appear as a seemingly innocent new pink or purple nodule in the skin. As a result, it is usually only their growth that attracts the attention of patients and doctors. The diagnosis is rarely made on appearance alone, and almost always requires a biopsy.
Merkel Cell Carcinoma Risk Factors
Sun exposure, fair skin, a weakened immune system, and advanced age are all factors that can increase the risk of developing this uncommon skin cancer. Merkel cell carcinoma is diagnosed in males more often than females. It is very unusual for Merkel cell carcinoma to happen in related family members.
Risk factors for developing Merkel cell carcinoma include:
Overexposure to UV Radiation
Exposure to ultraviolet (UV) radiation from the sun is the single most important cause of skin cancer. Some cases of Merkel cell carcinoma, especially those in sun-exposed areas like the head and neck, are also caused by sun exposure.
UV radiation is a spectrum of invisible rays that are part of the energy produced by the sun. There are two kinds of UV radiation: UVA and UVB. UVB radiation is well known for causing sunburn, and scientists believe these rays cause most skin cancers, including Merkel cell carcinoma. UVA is the dominant tanning ray and, according to the National Cancer Institute, may also cause skin damage that can lead to premature aging and skin cancer.
People who work outdoors, spend a lot of time at the beach, or regularly participate in outdoor sports have an increased risk of developing skin cancer. UVA rays can even travel through glass and clouds.
Sun lamps and tanning beds are another source of exposure to harmful UVA rays and should be avoided.
Merkel Cell Polyoma Virus
Researchers have linked a virus called the Merkel cell polyoma virus to many cases of Merkel cell carcinoma. However, most people have been exposed to the virus and will never develop Merkel cell carcinoma. For this reason, it remains unclear if or how the virus causes the disease and whether it could help guide future treatment.
People with fair skin — especially those with blond or red hair and blue or light-colored eyes — are more likely to develop skin cancer. (A tendency to freckle or sunburn can be a warning sign.) The skin of these particularly at-risk individuals contains less of the pigment melanin, which provides a degree of natural protection from the sun. People with dark skin can develop Merkel cell carcinoma, but this is exceedingly uncommon.
Weakened Immune System
People with a weakened immune system are also at an increased risk for developing Merkel cell carcinoma. Examples include those with HIV, leukemia, or lymphoma. People who are receiving chemotherapy or are being treated with medicines to prevent rejection after an organ transplant are also at an increased risk.
Merkel cell carcinoma becomes more common with increasing age. More than half of people with this cancer are diagnosed after the age of 70.
Merkel cell carcinoma is diagnosed slightly more often in males than in females.
Merkel Cell Carcinoma Symptoms
Merkel cell tumors usually appear as small, often shiny, painless bumps that range in color from flesh-toned to a bluish red. They are often mistaken for a bug bite, a cyst, or a basal cell carcinoma (another type of skin cancer). These tumors commonly arise on sun-exposed regions of the body, particularly the face or scalp. However, they can also appear on the arms, legs, trunk, and even areas of the body that are not exposed to sunlight, such as the buttock.
Like melanoma, another aggressive type of skin cancer, Merkel cell carcinoma can grow over a few weeks or months and can metastasize (spread) to nearby lymph nodes and other parts of the body. If the disease has spread to a lymph node, the node may feel enlarged. However, cancer could still be present even if it is not outwardly noticeable.