Merkel Cell Carcinoma Causes and Risk Factors

Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine skin cancer that forms in or just beneath the skin. It often develops on areas that receive substantial sun exposure, including the head, neck, arms, and legs.

MCC commonly appears as a single, firm, painless bump that grows quickly. The growth may be flesh-colored, red, or purplish. Because MCC can spread early, a new or rapidly changing skin lesion should be evaluated promptly.

What Causes Merkel Cell Carcinoma?

Merkel cell carcinoma develops when genetic changes cause abnormal cells in the skin to grow and divide without normal controls. These changes generally arise through one of two biological pathways: integration of Merkel cell polyomavirus into tumor cells or extensive DNA damage associated with ultraviolet radiation.

• Merkel cell polyomavirus: Approximately 80% of MCC tumors in the United States are associated with Merkel cell polyomavirus. The virus is common and usually causes no symptoms. In rare cases, viral DNA becomes integrated into a cell and produces proteins that interfere with normal growth controls, contributing to the formation of cancer.
• Ultraviolet radiation damage: Most virus-negative MCC tumors show extensive genetic damage associated with ultraviolet radiation. These tumors tend to contain numerous UV-related mutations.

Risk Factors for Merkel Cell Carcinoma

While knowing what triggers cellular mutations helps explain the biology of MCC, oncologists evaluate risk factors to determine a person's overall statistical likelihood of developing the disease.

Modifiable Risk Factors (Factors You Can Control)

• Sunlight and UV Exposure: Frequent, prolonged exposure to natural sunlight, especially during peak intensity hours, is the main modifiable risk factor associated with MCC. UV rays break down cellular DNA and impair local immune defenses in the skin.
• Indoor Tanning Equipment: Using tanning beds, booths, or sunlamps delivers concentrated UV radiation that directly accelerates genetic damage in skin cells.

Non-Modifiable Risk Factors (Factors You Cannot Change)

• Weakened Immune System (Immunosuppression): Individuals with compromised immune systems face a significantly elevated risk of MCC. This includes organ transplant recipients taking immunosuppressive medications, individuals living with HIV, and those undergoing treatments for autoimmune conditions or other blood cancers. Patients taking immune-suppressing medication should not stop or change their treatment without consulting the physician who prescribed it.
• Advanced Age: While MCC can occur at any age, the risk rises sharply over time. The majority of diagnoses occur in individuals over the age of 70, reflecting both cumulative sun exposure and natural age-related changes in immune function.
• Lighter Skin and UV-Sensitive Traits: People with fair skin, light hair (blond or red), light-colored eyes, or skin that burns easily have less natural melanin protection against UV-induced genetic damage.
• Personal History of Skin Cancers: A previous diagnosis of other skin malignancies, such as basal cell carcinoma, squamous cell carcinoma, or melanoma, is associated with an increased risk of MCC. This may reflect shared factors such as cumulative UV exposure, age, or immune function.

Can Merkel Cell Carcinoma Be Prevented?

Not every case of Merkel cell carcinoma can be prevented. However, reducing unnecessary UV exposure may lower risk, while regularly checking the skin can help patients notice changes that should be evaluated.

Practicing Sun Safety

Because UV exposure is a primary driver of skin cell mutations, daily sun protection is essential:

• Apply broad-spectrum, water-resistant sunscreen (SPF 30 or higher) every day, even on cloudy days.
• Wear protective clothing, wide-brimmed hats, and UV-blocking sunglasses when outdoors.
• Seek shade during peak sun intensity hours (10 a.m. to 4 p.m.).
• Avoid indoor tanning beds and sunlamps entirely.

Performing Regular Skin Self-Exams

Because MCC grows rapidly, catching it early requires active vigilance. Regularly examine your skin in a well-lit area and become familiar with existing spots, bumps, and marks. Pay particular attention to sun-exposed areas such as the face, scalp, neck, shoulders, arms, and legs.

MCC often appears as a firm, painless, flesh-colored, red, or purplish bump that enlarges quickly. Contact a dermatologist or another health care professional if you notice a new lesion that is growing rapidly or changing over several weeks or months.

Related Merkel Cell Carcinoma Causes and Risk Factors Information

The following FAQ-related article provides additional information about Merkel cell carcinoma causes and risk factors:

• Can other types of skin cancer lead to Merkel cell carcinoma?

Benefit from world-class care at Moffitt Cancer Center

Skin cancer research is a key area of focus at Moffitt, and we have a robust portfolio of clinical trials. Our Cutaneous Oncology Program is home to a multispecialty team of scientists and clinicians who are continually improving the preventive, diagnostic and treatment techniques for MCC, helping many patients achieve the best possible outcome and quality of life.

If you would like to learn more about Merkel cell carcinoma causes and risk factors, you can request an appointment with a specialist in Moffitt’s renowned Cutaneous Oncology Program by calling 1-888-663-3488 or submitting a new patient registration form online. We do not require referrals.