Merkel cell carcinoma: Causes, symptoms, and treatment

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Carcinoma is a type of cancer that develops in the skin or tissues covering or lining internal organs. Cancer occurs when cells begin to randomly divide and grow out of control. This cellular growth eventually forms a mass called a cancerous tumor.

MCC is one type of skin cancer, and its cells resemble Merkel cells. These are located close to the skin’s nerve endings and help provide a sense of light touch. They also relay information from the skin to the brain about details such as pressure and texture.

Merkel cells share traits with nerve and hormone-producing cells. As a result, they are classed as neuroendocrine cells, and MCC, in turn, is sometimes called neuroendocrine carcinoma of the skin. Another name for MCC is trabecular carcinoma.

MCC is very rare. In 2018, around 2,000 people in the United States received the diagnosis. However, its prevalence seems to be growing.

Between 2000 and 2013, the number of people diagnosed with MCC in the country increased by 95%. Experts estimate that by 2025, about 3,250 new cases of MCC will be diagnosed in the U.S. each year.

The increasing prevalence likely relates to the growing population of older adults in the U.S. Almost everyone with MCC is aged 50 or above.

MCC tends to develop on the head and neck, areas that have received the most sun exposure over time. The risk factors include:

• UV light exposure: Excessive or prolonged exposure to UV light can damage the DNA of genes that control skin cell growth, leading to skin cancer. The exposure usually results from spending time in the sun without protection, but tanning beds and phototherapy for psoriasis may also play a role.
• Older age: MCC is uncommon in people younger than 50, and 8 in 10 people with this cancer in the U.S. are 70 or older. This may be because skin damage increases over time and the immune system weakens with age.
• A weakened immune system: A healthy immune system helps destroy cancerous cells.
• Male sex: Males in the U.S. may be twice as likely as females to develop MCC.
• A lighter skin tone: People with this type of skin have a higher risk of MCC.
• A Merkel cell polyomavirus infection: Around 8 in 10 people with MCC have this virus in their cancerous cells. Many people contract the virus at some point, often during childhood, and it rarely contributes to MCC.

MCC usually develops on the:

• face
• neck
• arms
• legs

Rarely, it may form in the esophagus or nose, but it tends to affect areas that have been exposed to significant levels of UV light over time.

The symptoms of MCC can be similar to those of other, more common, types of skin cancer. However, MCC tumors:

• tend to be firm and raised
• may be pink, red, or purple
• are typically painless but can open up, becoming painful, bleeding sores or ulcers
• grow rapidly
• may resemble insect bites, cysts, or styes
• may spread, forming new, smaller lumps under the skin
• may cause surrounding lymph nodes to swell
• have an average diameter of 1.7 centimeters, about the same as a dime
• may be dome-shaped
• are almost never dark, as malignant melanoma tumors are
• are rarely scaly, as squamous cell carcinoma tumors are

To diagnose MCC, a doctor who specializes in skin diseases, cancer, or both will:

1. Examine the skin around the growth and feel the nearby lymph nodes.
2. Remove the affected skin cells or tumor for a closer examination.
3. If this confirms the presence of MCC, the person will undergo a sentinel lymph node biopsy (SLNB). This involves using very fine needles to take tiny samples from surrounding lymph nodes.
4. To learn more about the extent of the cancer, the doctor then uses PET and MRI scans and other tests.

Treating MCC is difficult because it tends to grow and spread rapidly. The best approach depends on factors such as:

• the person’s age
• their general health
• the location of the tumor
• the stage, or extent, of the cancer
• potential side effects of treatments
• the likelihood that each approach would eradicate the cancer or lead to significant improvements

Treatment options by stage

While various considerations help determine the best approach to treatment, the stage of MCC is often the most important factor.

Below, learn about the stages and the recommended treatments.

MCC without obvious spread

After having an SLNB to check whether the cancer has spread, most people undergo a wide local excision. This procedure removes the cancerous cells from the skin.

If MCC is on the face or other sensitive areas, a person may instead undergo Mohs micrographic surgery, which helps preserve more healthy skin.

Some people may also, or alternately, undergo radiation therapy, especially targeting the surrounding lymph nodes.

MCC with spread

This can be very difficult to cure. A person may need:

• surgery to remove affected cells
• radiation therapy
• chemotherapy
• immunotherapy drugs, such as pembrolizumab (Keytruda) or avelumab (Bavencio)

Recurring MCC

When MCC comes back, doctors often recommend a combination of:

• surgery to remove more of the affected tissue, possibly with surrounding lymph nodes
• radiation therapy
• chemotherapy
• immunotherapy drugs, such as Keytruda or Bavencio

Recurring MCC can be very difficult to treat, especially if it comes back in different areas. If this happens, doctors tend to focus on reducing symptoms, not curing the disease.

Some people also try complementary therapies for MCC, including:

• naturopathic medicine
• dietary changes
• immune-boosting supplements

The outlook for someone with MCC depends on the stage of the cancer, the treatment approach, and factors such as their age and the strength of their immune system.

About 78% of people with MCC that has not spread live for another 5 years after the diagnosis. This estimate is called a 5-year survival rate.

It is also worth noting that many people with this type of cancer experience a recurrence, often within 2–3 years of the initial diagnosis.

Many risk factors for MCC, such as age and male sex, are difficult or impossible to prevent. However, it can help to:

• Limit UV exposure.
• Stay in the shade when outdoors.
• Wear clothing that covers the body, including a hat, when outdoors.
• Wear sunscreen and sunglasses.
• Avoid sunlamps and tanning beds.
• Examine the skin monthly, and speak with a doctor about concerning changes as soon as possible.
• Have a healthful, balanced diet.
• Exercise regularly.
• Stay hydrated.
• Get enough rest.
• Use protection during sexual activity.
• Do not use intravenous drugs.
• Avoid secondhand smoke and, if applicable, quit smoking.

Anyone with a rapidly growing or spreading skin sore or growth should contact a doctor as soon as possible. Receiving treatment for MCC early reduces the risk of complications and improves the outlook.

When seeking treatment for MCC, be sure to find a specialist who has experience with this disease. This doctor should also be working with a dermatopathologist, a doctor who specializes in diagnosing skin conditions.