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Skin cancer types: Merkel cell carcinoma causes

Who gets Merkel cell carcinoma?

Merkel cell carcinoma (MCC) is rare, which makes it harder to study. For this reason, scientists are still not entirely sure what causes it. They have learned a lot, however, by looking at cancer records.

It’s through cancer records that they discovered the people most likely to get MCC have all the following traits:

  • Male

  • 65 years of age or older

  • Fair skin that may burn or freckle when exposed to the sun

  • Seldom used sunscreen, clothing, or shade to protect their skin from the sun

This finding has given scientists insight into what may cause this rare skin cancer. It appears that sunlight and a weakened immune system play key roles.

A virus may also play a role in causing MCC.

The following explains why scientists believe each of these (sunlight, a weakened immune system, and a virus) may play a role in causing MCC.

Risk increases with age

The risk of developing Merkel cell carcinoma increases with age, and people who are older than 65 years of age have the greatest risk.1

Shot of a happy elderly couple on the beach

What causes Merkel cell carcinoma?

Scientists have proven that the sun’s ultraviolet (UV) light can cause skin cancer. We know that every time UV light hits our skin, it can damage some of the DNA inside our skin’s cells. People who have fair skin and seldom protect their skin from the sun are most susceptible to this damage.

The body tries to repair this damage. Over the years, the damage becomes more than the body can handle. This leads to changes (mutations) in our skin’s cells. As the mutations build up, skin cancer can develop.

It seems clear that the sun’s UV light plays a role in causing MCC. This skin cancer is most common in fair-skinned men who rarely protected their skin from the sun.

We also know that more people are diagnosed with MCC in Hawaii, which has the strongest UV light in the United States, than in any other state. Worldwide, Australia, which receives intense UV light, has the greatest number of people who develop MCC.

More evidence that UV light plays a role in causing MCC comes from this finding. People who have psoriasis and receive a treatment called PUVA (psoralen plus UVA light) have a 100 times greater risk of developing MCC than do other people.

If you have psoriasis and treat it with PUVA, it’s important to keep in mind that MCC is very rare.

Weak immune system
Our immune system helps protect us from disease. Anything that weakens our immune system increases our risk of developing many diseases, including skin cancer. Scientists believe that the immune system plays a key role in whether someone develops MCC because this skin cancer tends to develop in people who:

  • Are older than 65 years of age

  • Take certain medications, such as medication that suppresses the immune system in order to prevent the body from rejecting a transplanted organ

  • Live with a condition that significantly weakens the body’s immune system, such as HIV or AIDS

It may seem strange that our age affects our immune system. Scientists have found that as we age, our immune system gradually declines. We get infections more easily. Vaccines may not work as well as they did when you were younger.

It’s believed that a weakening immune system is the reason MCC usually develops after 65 years of age and why the risk of developing this skin cancer continues to increase with age.

MCC rarely develops in young people.

Merkel cell polyomavirus (MCP)
Two scientists discovered this virus in 2008 while studying MCC. What they learned is that people in the United States who develop MCC often have both:

  • A weakened immune system

  • The MCP virus

As they continued to study this virus, scientists learned that between 60% and 80% of Americans carry this virus. Testing shows that it can live on our skin, in our urine, and inside our nose without causing a health problem. We now know that most Americans become infected with this virus as a child, usually by 4 or 5 years of age.

What scientists want to know is why so many people carry this virus, yet so few people get MCC. It may be that the years of UV damage to the skin and a weakened immune system cause the virus to mutate (change). These changes to the virus may cause MCC. More research is needed find out whether this happens.

Scientists also want to know why Australians who get MCC rarely have the MCP virus inside their MCC tumor, and why most Americans do.

While there are still plenty of questions to be answered, the discovery that that the immune system plays a key role in MCC is changing the way this cancer is treated. Newer treatments that help the immune system find and destroy cancer cells have become a treatment option for advanced MCC, and researchers continue to study new treatments.

You can learn about this and other treatments for MCC at, Merkel cell carcinoma: Diagnosis and treatment.

1 Paulson KG, Park SY, et al. “Merkel cell carcinoma: Current US incidence and projected increases based on changing demographics.” J Am Acad Dermatol 2018;78:457-63.

Getty Images

Coggshall K, Tello TL, et al. “Merkel cell carcinoma: An update and review Pathogenesis, diagnosis, and staging.” J Am Acad Dermatol. 2018;78:433-42.

Tello, TL. Coggshall K, et al. “Merkel cell carcinoma: An update and review Current and future therapy.” J Am Acad Dermatol. 2018;78:445-54.