The first symptom of Merkel cell carcinoma most often is a growth on the skin. This skin cancer can happen anywhere on the body. It happens most often on skin that typically gets sunlight. In white people, the growth is most likely to be on the head or neck. In Black people, the growth more often is on the legs.

A Merkel cell carcinoma can cause:

• A bump on the skin that often is painless.
• A bump that grows quickly.
• A bump whose two sides don't match.
• A bump that looks pink, purple, red-brown, or the same color as the skin around it.

When to see a doctor

Make an appointment with a healthcare professional if you have a mole, freckle or bump that changes size, shape or color. Also see a healthcare professional if you have a bump that grows fast or bleeds easily after minor injury, such as washing your skin or shaving.

It's often not clear what causes Merkel cell carcinoma.

This skin cancer happens when cells in the skin develop changes in their DNA. A cell's DNA holds the instructions that tell the cell what to do. In healthy cells, the DNA gives instructions to grow and multiply at a set rate. The instructions tell the cells to die at a set time.

In cancer cells, the DNA changes give other instructions. The changes tell the cancer cells to grow and multiply at a fast rate. Cancer cells can keep living when healthy cells would die. This causes too many cells.

The cancer cells might form a mass called a tumor. The tumor can grow to invade and destroy healthy body tissue. In time, cancer cells can break away and spread to other parts of the body. When cancer spreads, it's called metastatic cancer.

Merkel cell carcinoma is named for the cells where experts once thought it started. The Merkel cells are found at the bottom of the outer layer of skin. The Merkel cells are connected to the nerve endings in the skin that play a role in the sense of touch. Healthcare professionals no longer believe that this cancer starts in the Merkel cells. They don't know exactly what kind of cells it starts in.

It's often not clear what causes the DNA changes that lead to Merkel cell carcinoma. Researchers have found that a common virus plays a role in causing Merkel cell carcinoma. The virus, called Merkel cell polyomavirus, lives on the skin. It doesn't cause symptoms. Experts don't know exactly how this virus causes Merkel cell carcinoma.

Factors that may raise the risk of Merkel cell carcinoma include:

• Skin that sunburns easily. Anyone of any skin color can get Merkel cell carcinoma. But it's more common in people who have less melanin in their skin. Melanin is a substance that gives color to skin. It also helps protect the skin from damaging rays from the sun.

  People with Black or brown skin have more melanin than do people with white skin. So white people are more likely to get Merkel cell carcinoma than are people with Black or brown skin.

• Too much UV light. Ultraviolet light, also called UV light, raises the risk of Merkel cell carcinoma. UV light can come from the sun. Being in the sun without covering the skin with clothing or sunblock raises the risk of Merkel cell carcinoma. UV light for treatment of the skin condition psoriasis also can raise the risk of this skin cancer.
• Tanning bed use. People who use indoor tanning beds have a higher risk of Merkel cell carcinoma.
• A weakened immune system. People with weakened immune systems are more likely to get Merkel cell carcinoma. A weakened immune system can happen in people with certain health conditions, such as HIV infection and chronic leukemia. It also can happen in people taking certain medicines, such as medicines that lower the immune response.
• History of other skin cancers. Merkel cell carcinoma is linked to other skin cancers, such as basal cell carcinoma and squamous cell carcinoma.
• Older age. The risk of Merkel cell carcinoma goes up with age. This cancer is most common in people older than age 50, though it can happen at any age.

Even with treatment, Merkel cell carcinoma often spreads to other parts of the body. When cancer spreads, healthcare professionals sometimes say it metastasizes. Merkel cell carcinoma tends to travel first to nearby lymph nodes.

Later it may spread to the brain, bones, liver or lungs. It can keep these organs from working as they should. Cancer that spreads is harder to treat and can be fatal.

While exposure to sunlight isn't proved to cause all Merkel cell carcinomas, it is thought to be a risk factor for this cancer. Getting less sun exposure may lower your risk of skin cancer.

Try to:

Stay out of the sun in the middle of the day

For much of North America, the sun's rays are strongest between about 10 a.m. and 3 p.m. Plan to be outdoors at other times of the day, even during winter or when the sky is cloudy. When outside, stay in the shade as much as possible.

Wear sunscreen year-round

Use a broad-spectrum sunscreen with an SPF of at least 30, even on cloudy days. Apply sunscreen generously. Reapply every two hours, or more often if you're swimming or sweating.

Wear protective clothing

To protect your skin from the sun, wear dark, tightly woven clothes that cover the arms and legs. Wear a wide-brimmed hat that shades the face and ears.

Don't forget sunglasses. Look for sunglasses that block both types of ultraviolet light, also called UV light, that comes from the sun. The two types are UVA and UVB.

Check your skin often

Look at your skin often for new growths or changes in moles, freckles, bumps and birthmarks. Use mirrors to check your face, neck, ears and scalp. Report any changes to your healthcare professional.

Even though Merkel cell carcinoma most often is on the face, head and neck, look at other areas of your body. Look at your chest and trunk and the tops and undersides of your arms and hands. Look at the front and back of your legs and your feet. Look at the bottom of the feet and the spaces between your toes. Also check your genital area and between your buttocks.

Merkel cell carcinoma diagnosis often starts with an exam. A healthcare professional may look at your skin and remove a sample of cells for testing. This skin cancer may be hard to diagnose because it may look like other skin growths.

Physical exam

During a physical exam, a healthcare professional looks at your skin for moles, freckles and other growths.

Biopsy

A biopsy is a procedure to remove a sample of tissue for testing in a lab. For Merkel cell carcinoma, a healthcare professional may use a tool to cut away some of the concerning skin. Other ways to do a skin biopsy involve using a shaving tool or a circular cutting tool to get some of the skin. The sample is tested in a lab to see if it is cancer.

Tests for cancer that spreads

Your healthcare professional may use other tests to find out whether the cancer has spread beyond your skin. These other tests may include:

• Sentinel node biopsy. A sentinel node biopsy is a procedure to see whether cancer has spread to the lymph nodes. This procedure involves putting a dye into the skin near the cancer. The dye then flows through the lymphatic system to the lymph nodes.

  The first lymph nodes that get the dye are called the sentinel nodes. A healthcare professional removes these lymph nodes and looks for cancer cells under a microscope.

• Imaging tests. Imaging tests used to look for signs that the cancer has spread include a chest X-ray, a CT scan of the chest and belly, and a positron emission tomography scan, also called a PET scan.

Treatment for Merkel cell carcinoma most often involves surgery to remove the cancer. If the cancer has spread beyond the skin, treatment may involve medicines or radiation.

Surgery

A surgeon removes the cancer along with a border of skin that doesn't have cancer. For cancer that has spread to lymph nodes near the skin cancer, the surgeon removes those lymph nodes. This is called a lymph node dissection.

Surgery most often involves a scalpel to cut away the cancer. Sometimes, a surgeon may use a procedure called Mohs surgery.

Mohs surgery involves cutting away thin layers of skin. The surgeon uses a microscope to look at each layer for cancer. The process keeps going until there's no more cancer. The goal of Mohs surgery is to remove all the cancer without harming the healthy skin around it.

Radiation therapy

Radiation therapy treats cancer with powerful energy beams. For Merkel cell carcinoma, a healthcare professional may use radiation therapy after surgery to destroy cancer cells that remain. Radiation may be the only treatment for people who don't want to have surgery. Radiation also can treat cancer that has spread.

Immunotherapy

Immunotherapy for cancer is a treatment with medicine that helps the body's immune system kill cancer cells. The immune system fights off diseases by attacking germs and other cells that shouldn't be in the body. Cancer cells survive by hiding from the immune system. Immunotherapy helps the immune system cells find and kill the cancer cells.

Most often, immunotherapy treats Merkel cell carcinoma that comes back after treatment or spreads to other areas of the body.

Chemotherapy

Chemotherapy treats cancer with strong medicines. Healthcare professionals don't often use chemotherapy to treat Merkel cell carcinoma. But your healthcare team may suggest it if your Merkel cell carcinoma spreads to your lymph nodes or other organs, or if it returns after treatment.

If you have a mole, freckle or bump on your skin that concerns you, start by making an appointment with a healthcare professional. For skin cancer, you'll likely be sent to a skin specialist, called a dermatologist.

Here's some information to help you get ready for your appointment.

What you can do

Ask a family member or friend to go with you to help you remember the information you get.

Make a list of:

• Your symptoms and when they began. Include any that don't seem linked to the reason you made the appointment.
• Key personal information. Include major stresses or recent life changes.
• Medical information. Include other conditions you have or conditions that run in your family.
• All medicines, vitamins or supplements that you take. Include the dosages.
• Questions to ask your healthcare professional.

For Merkel cell carcinoma, questions might include:

• What is likely causing my symptoms or condition?
• Are there other possible causes for my symptoms or condition?
• What tests do I need?
• What treatments are there?
• I have other health conditions. How can I best manage them together?
• Are there brochures or other printed material I can have? What websites do you suggest?

Be sure to ask all the questions you have.

What to expect from your doctor

Your healthcare team is likely to ask you questions, such as:

• How have your symptoms changed over time?
• Does anything make your symptoms better?
• 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 used for those conditions?
• Have you been diagnosed with any immune system conditions? If so, what treatments have you used?