Merkel cell carcinoma, also called neuroendocrine cancer of the skin, is an aggressive type of skin cancer that affects only about 400 people in the United States each year. But like other skin cancers, that number is growing.
A normal Merkel cell is a cross between a nerve cell and an endocrine (or hormone-producing) cell located on or just below the skin in the underlying tissue, and functions predominantly as a touch receptor. Merkel cell carcinoma occurs when these cells begin to grow uncontrollably.
An example of Merkel cell carcinoma.
Merkel cell tumors typically arise on, but are not limited to, sun-exposed parts of the body such as the face and neck. Their shape and color are less distinctive than other skin cancers, and they can often appear as an innocent pink pearly nodule. As a result, it is usually only the speed with which they grow that attracts the attention of patients and their doctors.
With early detection and treatment, Merkel cell carcinoma can be well contained and even cured. Treatment becomes more difficult as the tumor grows and spreads, but aggressive therapy can still lead to high rates of survival.
Sun exposure, fair skin, a weakened immune system, and older age are all factors that can increase the risk of developing this uncommon skin cancer. Infection with the Merkel cell virus may also be a factor in Merkel cell carcinoma. Men are at a slightly increased risk of the disease than women. No genetic link has been found.
Risk factors for developing Merkel cell carcinoma include:
Overexposure to UV Radiation
Overexposure to ultraviolet (UV) radiation from the sun is the single most important cause of skin cancer. Merkel cell carcinoma is no exception.
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.
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 propensity 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, however, can still develop Merkel cell carcinoma.
Weakened Immune System
People with a weakened immune system are also at an increased risk for developing Merkel cell carcinoma. Examples include certain patients with HIV, leukemia, or lymphoma. People on chemotherapy or treated with drugs to prevent organ transplant rejection are also at an increased risk. Transplant patients who develop Merkel cell carcinoma can be treated by lowering the dose of immune suppressants.
Merkel cell carcinoma becomes more common with age. More than half of patients are diagnosed after the age of 65.
Some evidence suggests that Merkel cell carcinoma is slightly more common among men than women.
Merkel Cell Virus
Recently, researchers have linked a virus to many cases of Merkel cell carcinoma. However, it remains to be determined if the Merkel cell polyomarvirus causes the disease, and if it might help guide future treatment. If so, the virus could offer promising new targets for immunotherapy.
Merkel cell tumors usually appear as small, often shiny, painless lumps that range in color from flesh toned to bluish-red. They are often mistaken for a bug bite or a basal cell carcinoma. 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 rapidly 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, it may feel enlarged. However, cancer could still be present even if it is not outwardly noticeable.
Prevention & Early Detection
There are some measures you can take to reduce your risk of contracting Merkel cell carcinoma and other skin cancers.
Skin cancer expert Isaac Brownell describes the tools that can be used to detect skin cancers and prevent unnecessary procedures.
Avoid Exposure to the Sun
The best way to prevent skin cancer is to protect yourself from excessive exposure to sunlight — and not only when you go to the beach. Skin cancer prevention should be practiced every day by seeking shade, wearing protective hats and clothing, avoiding the midday sun and tanning beds, and using broad-spectrum sunscreen (one that protects against UVA and UVB rays), even on cloudy days. Look for an SPF of at least 30, and apply two thin coats (about an ounce per application) as part of your daily routine. Be sure to reapply every two hours if swimming or sweating.
Screening and Skin Examination
Doctors at Memorial Sloan Kettering do not recommend regular screening for non-melanoma skin cancers. However, any suspected skin cancer should be brought to the attention of a physician or dermatologist immediately. Merkel cell carcinoma has a good chance of being cured if detected early, and early treatment minimizes the risk of serious cosmetic damage or functional difficulties.
During a skin examination with a dermatologist, your doctor will usually look at new growths, spots, or bumps on your skin to determine whether they might be cancerous or precancerous. After the examination, the doctor will show you how to examine your own skin and determine whether any growths have changed in appearance.
Merkel cell carcinomas are unlike other skin cancers in that they typically don't appear with an alarming asymmetrical shape or pigmented color. Rather, they can look innocuous, even like a bug bite. Patients may want to pay particular attention to any pearly bumps that appear to be growing. This visual inspection should cover the entire surface of the skin, including places where the sun may not reach, such as the scalp, the soles of the feet, and between the toes.