What Is Merkel Cell Carcinoma?

Merkel cells are found just below your skin’s surface, on the lowest level of your top layer of skin (the epidermis). Connected to nerve endings associated with the sensation of pressure, Merkel cells play a key role in helping us identify fine details and textures by touch. 

What is Merkel cell carcinoma? 

Merkel cell carcinoma is a rare aggressive skin cancer. The name was given to the cancer because of the cancer cells’ resemblance under the microscope to Merkel cells, however, the true cell of origin is likely to be another skin cell such as a squamous skin cell or a hair follicle cell. This disease usually appears as a painless skin nodule (bump or lump) that grows very rapidly. The tumors can be skin-colored, red, or violet, most often developing in areas of skin exposed to the sun, especially the face, head, and neck. But these nodules can develop anywhere on the body, even areas not often exposed to sunlight. 

Staying safe in the sun can reduce your risk of Merkel cell carcinoma and other types of skin cancer. 

Merkel cell carcinoma can grow quickly and spread to other parts of the body, making it a particularly dangerous form of skin cancer. Treatment options usually depend on whether the cancer has spread beyond the skin, but can include surgery (to remove the cancer), radiation therapy, and immunotherapy. 

What causes Merkel cell carcinoma? 

Merkel cell carcinoma can be caused by one of two things — either UV damage from the sun or changes in a cell because of the Merkel cell polyomavirus. There are tests available which can determine what was the cause of a person’s MCC. MCC most often develops in people aged 60 or older and in people with weakened immune system. Long-term exposure to sunlight is considered a risk factor, so it’s important to always stay safe in the sun to reduce your risk of Merkel cell carcinoma and other types of skin cancer

To help prevent problems, check your skin regularly. If you notice a mole, freckle, or bump has changed in color, size, or shape, talk to your doctor. Most skin nodules don’t become cancer, but catching cancer in its early stages can dramatically improve treatment outcomes. 

What are the symptoms of Merkel cell carcinoma? 

Merkel cell carcinoma appears on the skin, usually as a single red or violet-colored lump that is firm and raised. It will typically grow quickly and be painless.  

Check with your doctor if you see any changes in your skin. 

What happens when Merkel cell carcinoma spreads? 

Cancer cells can break from the original tumor and spread throughout the body via the bloodstream or lymphatic system. This process is called metastasis. 

At its earliest stage, stage I, the Merkel cell carcinoma is localized to one spot in the skin. In stage II, the tumor has grown beyond 2 centimeters and may have spread to nearby connective tissue, muscle, cartilage, or bone. 

In stage III, the cancer has spread into lymph nodes. In stage IV, the tumor has spread to skin that is not close to the primary tumor or it has spread to other organs, such as the liver, lung, bone, or brain. 

How is Merkel cell carcinoma treated? 

Merkel cell carcinoma has different treatments depending on how advanced the cancer is: 

  • For stage I and stage II Merkel cell carcinoma, in which the tumor is small and has only spread to nearby tissue, treatment usually includes surgery to remove the tumor followed by radiation therapy. 
  • For stage III Merkel cell carcinoma, treatment will include surgery to remove the tumor (if possible), followed by radiation therapy. Patients may also choose to enter a clinical trial of chemotherapy, immunotherapy, or other novel therapies.  

Learn more about clinical trials for Merkel cell carcinoma at Dana-Farber here.  

  • Stage IV Merkel cell carcinoma is treated with a type of immunotherapy called an immune checkpoint inhibitor. Treatment might also include chemotherapy, surgery, or radiation therapy to relieve symptoms. Patients may also choose to enter a clinical trial. 
  • Unfortunately, it is common for Merkel cell cancer to recur after treatment, reappearing in lymph nodes, skin, or other organs. Treatment of recurrent Merkel cell carcinoma may include surgery followed by radiation therapy and/or chemotherapy. Enrollment in a clinical trial is also an option.  

How does one monitor cancer recurrence after treatment? 

Merkel cell carcinoma can come back after treatment is completed. Therefore, it is important to follow up with your doctors for monitoring. This can happen through regular visits to your cancer doctor for physical examinations, and as well as blood tests and imaging.