Merkel cell carcinoma is a rare type of skin cancer that usually appears as a flesh-colored or bluish-red nodule, often on your face, head or neck. Like other types of skin cancers, the incidence of Merkel cell carcinoma is increasing worldwide.

Merkel cell carcinoma, also called neuroendocrine carcinoma of the skin, most often develops in older people. Long-term sun exposure or having a weak immune system may increase your risk of developing Merkel cell carcinoma.

Merkel cell carcinoma tends to grow fast and to spread quickly (metastasize) to other parts of your body, so it's critical to catch and treat it early. Your treatment plan will depend on whether the cancer has spread beyond your skin by the time it's diagnosed.

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Merkel cell carcinoma

The first sign of Merkel cell carcinoma is usually a fast-growing, painless nodule (tumor) on your skin. The shiny nodule may be skin colored or may appear in shades of red, blue or purple. Nearly half of 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.

If the skin cancer has spread to other parts of your body, you may experience swollen lymph nodes, pain or fatigue.

When to see a doctor
If you notice a mole, freckle or bump that is changing in size, shape or color, growing rapidly or bleeding easily after minor trauma, such as washing your skin or shaving, talk to your doctor. Most skin lesions never become cancer, but if you see any changes, it's important to get checked out.

Merkel cell carcinoma is named after the Merkel cell, which is found at the base of the outermost layer of your skin (epidermis). Merkel cells may be associated with the sense of touch.

It's not certain what causes Merkel cell carcinoma to develop. One theory is that Merkel cell carcinoma may arise from the Merkel cell itself. Or it may be that certain immature cells (skin stem cells) become cancerous and develop features that make them look like Merkel cells.

Researchers have detected a number of genetic abnormalities in Merkel cell carcinoma cells. However, it's not known how these genetic changes affect cancer development.

While there's no definite cause of Merkel cell carcinoma, a number of factors may increase your risk of developing this cancer:

• Natural or artificial sunlight. Being exposed to natural sunlight or artificial light, including tanning beds, increases your risk. 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 or those taking drugs that suppress the immune response — 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.
• Age. Older people are at an increased risk of developing Merkel cell carcinoma, especially those older than age 70. Younger people who develop this cancer usually have weakened immune systems.
• Race. 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.

Merkel cell carcinoma is an aggressive cancer and complications are not uncommon:

• Metastasis. Even with treatment, up to half the people with Merkel cell carcinoma eventually develop cancer that spreads beyond the skin. Merkel cell carcinoma tends to travel first to nearby lymph nodes and then may spread to your liver, bone, lungs or brain, where it can interfere with the functioning of these organs. Cancer that has metastasized is more difficult to treat and can be fatal.
• Treatment side effects. Although radiation therapy and chemotherapy may be effective in halting cancer growth, these therapies can also kill healthy cells and cause complications.

You're likely to start by first seeing your family doctor or a general practitioner. However, in some cases when you call to set up an appointment, you may be referred immediately to a skin specialist (dermatologist).

Here's some information to help you be well prepared for your appointment, and what to expect from your doctor.

What you can do

• Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance to prepare for tests you're likely to receive.
• Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment. For example, your doctor will want to know if you've noticed a change in your energy level. Also be prepared to tell your doctor when you first noticed a change in your skin, and how the lesion may have changed since then.
• Make a list of your key medical information, including other conditions for which you're being treated and the names of all medications that you're taking.
• Take a family member or friend along, if possible. Sometimes it can be difficult to soak up all the information provided to you during an appointment. Someone who accompanies you may remember something that you missed or forgot.
• Write down questions to ask your doctor.

Your time with your doctor is limited, so preparing a list of questions ahead of time will help you make the most of your appointment. List your questions from most important to least important in case time runs out. For Merkel cell carcinoma, some basic questions to ask your doctor include:

• What is likely causing my symptoms or condition?
• Other than the most likely cause, what are possible causes for my symptoms or condition?
• What kinds of diagnostic tests do I need? How are these tests performed?
• What are my treatment options?
• How will you check my response to treatment?
• How likely is my condition to recur? What treatment options would be available in that case?
• What follow-up tests will I need to monitor for recurrence?
• I have these other health conditions. How can I best manage them together?
• Are there any restrictions that I need to follow?
• Should I see a specialist? What will that cost, and will my insurance cover seeing a specialist?
• Are there any brochures or other printed material that I can take home with me? What Web sites do you recommend visiting?

In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask questions during your appointment at any time that you don't understand something.

What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:

• When did you first notice your symptoms?
• How have your symptoms changed over time?
• Does anything seem to improve your symptoms?
• Have you spent a lot of time in the sun, or have you used tanning beds?
• Do you have a history of other skin conditions, such as skin cancer or psoriasis? What treatments have you received for those conditions?
• Have you been diagnosed with any immune system disorders? If so, what treatments have you received?
• Have you been diagnosed or treated for any other health conditions?

Diagnosis of Merkel cell carcinoma involves the following:

• Physical exam. Examining unusual moles, freckles, pigmented spots and other growths on your skin is the first step your doctor will likely take in making a diagnosis. A careful physical exam is important, because it's difficult to distinguish Merkel cell carcinoma from other skin cancers, including basal cell carcinoma. The nodule on your skin may also resemble other skin growths or even harmless cysts.
• Biopsy. After removing the tumor or a sample of the tumor from your skin, your doctor treats the cells with a special stain for viewing under the microscope.

Determining the extent
Your doctor may use the following tests to help determine whether the cancer has spread beyond your skin:

• Sentinel node biopsy. When cancer cells spread, they often travel first to your lymph nodes. Lymph nodes are small, rounded structures that filter foreign particles from lymph, a tissue-cleansing fluid in your body. This procedure involves injecting a dye near the skin tumor. 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.
• Other diagnostic tests. Imaging tests, such as X-ray or a computerized tomography (CT) scan, provide pictures of your body organs and structures. You'll likely have a chest X-ray and a CT scan of your chest and abdomen to help your doctor 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 a radioactively tagged hormone to check for the spread of Merkel cell carcinoma.

The type of treatment you'll receive depends on whether the cancer has spread beyond your skin by the time it's diagnosed. You might have just one type of treatment or a combination of treatments:

• Surgery. During surgery, your doctor removes the tumor along with a border of normal skin surrounding the tumor. Removing a border of normal skin helps catch any remaining cancer cells. 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).

  Occasionally, your doctor may use a procedure called Mohs micrographic surgery. After removing the visible tumor, your doctor creates "slices" of the tumor tissue and examines each slice under a microscope. The process is repeated until cancer cells are no longer visible in the tissue slice. This type of surgery takes out less normal tissue — thereby reducing scarring — but ensures a tumor-free border of skin. Mohs surgery is often used to remove skin cancer from the face.

• Radiation therapy. Radiation therapy involves directing high-energy X-rays at cancer cells. Radiation damages the genetic material in growing cells. Cancer cells are particularly susceptible to the effects of radiation because they divide more rapidly than normal cells do.

  In cases of Merkel cell carcinoma, radiation therapy is usually given to kill any cancer cells that remain after the tumor is removed. Because this type of cancer is so rare, there's no established consensus about who should receive radiation after surgery completely removes a tumor. Talk with your doctor about the pros and cons of radiation after surgery in your particular situation.

  Radiation may be used to shrink Merkel cell carcinoma before it's removed or as the sole treatment in people who choose not to undergo surgery. Radiation can also be used to treat areas of metastases that are causing symptoms.

  General side effects from radiation therapy include red, irritated skin, fatigue and hair loss if the scalp needs to be radiated. If you receive radiation therapy to your head or neck, you may notice that you have a dry mouth, difficulty swallowing and other symptoms.

• Chemotherapy. Chemotherapy uses drugs to kill the cancer cells or stop them from dividing. Depending on the type of drug, chemotherapy may be injected, swallowed or applied to your skin.

  Chemotherapy is generally used when Merkel cell carcinoma has spread to other organs in your body or when it has recurred. However, whether chemotherapy improves the survival rate in people with Merkel cell carcinoma is unclear. Talk with your doctor about the benefits and risks of using chemotherapy in your case.

  Chemotherapy often causes significant side effects, most of which are temporary. Common side effects include nausea, vomiting and diarrhea; hair loss; fatigue and an increased risk of infection. Rarely, permanent damage to your body organs may occur.

During the course of treatment, you'll undergo physical exams, including blood tests, to monitor how you're responding to radiation therapy or chemotherapy. Afterward, you'll continue having frequent checkups with your doctor to watch for recurrences.

The outlook after treatment for Merkel cell carcinoma varies, depending on a number of factors. These include the stage of the tumor at diagnosis, your age, the tumor size and location, and whether you have other health conditions. Generally, otherwise healthy people with small tumors and no evidence of cancer spreading beyond the skin tend to have the best prognoses.

While sunlight isn't proved to cause Merkel cell carcinoma, it's a risk factor for this cancer, other skin cancers and premature aging. Here are a few ideas for maintaining healthy skin:

• Be 'sun smart.' Avoid sun exposure as much as possible from 10 a.m. to 4 p.m. — the most intense sunlight hours of the day. If you're outdoors, seek shade under an umbrella or tree.
• Shield your skin and eyes. Wear a wide-brimmed hat, tightly woven clothing and sunglasses with ultraviolet light (UV) protection. You'll look stylish and help prevent sun damage to your skin.
• Apply sunscreen liberally and often. Apply sunscreen with a sun protection factor (SPF) of 15 or greater when you head outdoors. Remember to reapply sunscreen after swimming or if you've been sweating.
• Watch for changes. If you notice a mole, freckle or bump that's changing in size, shape or color, talk to your doctor. Most skin lesions never become cancer, but catching cancer in its early stages increases the chances that treatment will be successful.

Merkel cell carcinoma can't be prevented. However, you may be able to reduce your risk of this cancer and other skin cancers by limiting your exposure to sunlight.