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Merkel Cell Carcinoma (MCC)


With age comes worry about your health. For instance, as you get older you may be motivated to begin checking your skin for abnormalities that could be cancer. When doing so, you may focus on looking for dark spots, such as moles that have changed in size or shape. 

But it’s also important to know that if a raised, reddish-purplish spot appears on your skin, it’s worth bringing it to your doctor’s attention. Although rare, such a raised area might, in fact, be Merkel cell carcinoma, an aggressive form of skin cancer.  

Merkel cell carcinoma is most common among fair-skinned people of European ancestry, but can affect individuals with a darker complexion as well. It is frequently diagnosed in adults—men more commonly—aged 65 and older, particularly among those who have had a lot of sun exposure over their lifetime. (It usually appears in sun-exposed areas, but can present in sun-shielded areas, too.) 

Younger people are occasionally diagnosed with Merkel cell carcinoma, but they typically have health conditions that have compromised their immune systems, such as organ transplantation or HIV.  

Although Merkel cell carcinoma is one of the most dangerous form of skin cancer, the majority (76%) of people survive five years or more after diagnosis when the cancer has not spread. But those numbers worsen if the cancer spreads locally or to distant locations in the body, underlining the importance of early detection and treatment.  

“In the past, once the cancer spread beyond its original site in the skin and beyond the draining lymph nodes, the prognosis was very poor,” says Smilow Cancer Hospital medical oncologist Harriet Kluger, MD. “Traditional chemotherapy shrinks metastatic Merkel cell tumors approximately 50% of the time, but the duration of shrinkage was very short.”

However, promising new research, including studies of newer drugs conducted at Yale and partnering institutions, has yielded benefits for patients. “With contemporary immunotherapy, many patients with metastatic Merkel cell carcinoma are living for years, and some might have complete, durable responses,” says Dr. Kluger.

What is Merkel cell carcinoma?

Merkel cell carcinoma is a type of skin cancer that tends to develop on the head, neck, or any area of skin that is regularly exposed to the sun. However, it can appear on the trunk as well, including in areas that have not been exposed to the sun.  

It appears as a hard, raised, rounded, reddish-purplish bump that grows quickly over the course of several weeks or months. The spot usually doesn’t cause pain or discomfort, but it tends to grow rapidly and may spread to other body parts.  

The cancer forms in special “Merkel” cells in the skin—a type of neuroendocrine cell that combines qualities from cells of both the nervous and endocrine systems. They’re located near the nerve endings within the skin, and, when functioning normally, help people recognize the sensation when something or someone touches their skin very gently. Merkel cell carcinoma develops when something causes these cells to grow uncontrollably.

What causes Merkel cell carcinoma?

Doctors don’t yet know the exact cause of Merkel cell carcinoma, but it is linked to Merkel cell polyomavirus, a virus that has been found in about 80% of biopsied samples of Merkel cell carcinoma cells. It’s believed that Merkel cell polyomavirus triggers the formation of a tumor.  

Sometimes, a patient may be diagnosed with Merkel cell carcinoma—but Merkel cell polyomavirus isn’t present within the cancer cells. It’s thought that a suspected link between long-term exposure to ultraviolet radiation and cancer growth among susceptible people may explain these cases.

What are the symptoms of Merkel cell carcinoma?

People who have Merkel cell carcinoma may notice a new bump on their skin that has some or all of the following qualities:

  • Reddish-purple color (sometimes pinkish or bluish)
  • Raised and rounded, like a dome
  • Hard to the touch
  • Painless
  • Shiny, smooth skin
  • Expanding in size over a short period of time

What are the risk factors for Merkel cell carcinoma?

People with fair skin who are of European ancestry are at a greater risk of Merkel cell carcinoma. It’s more common among older adults and males.  

Other risk factors for Merkel cell carcinoma include:

  • A history of chronic exposure to ultraviolet light (sun exposure)
  • Previous infection with Merkel cell polyomavirus
  • HIV, which may suppress the immune system
  • Use of immune-suppressing drugs after organ transplantation or for autoimmune diseases
  • Cancer treatments, which suppress the immune system
  • Other types of cancer, including melanoma, multiple myeloma, or chronic lymphocytic leukemia

How is Merkel cell carcinoma diagnosed?

When doctors suspect Merkel cell carcinoma, they will examine the area, obtain a health history from the patient, and perform a biopsy to diagnose the condition.  

Merkel cell carcinoma has a distinct look, but when the tumor is small, it can be confused with other skin conditions, such as acne. When a person has a rounded, raised, reddish or purplish bump on the head, neck, or other sun-exposed skin, he or she may be asked about lifetime sun exposure, history of skin or other types of cancer, and whether he or she has any immune-suppressing health conditions.  

Doctors will biopsy the site to check for the presence of Merkel cell carcinoma cells. A blood test may also be used to check for the presence of Merkel cell polyomavirus antibodies. However, the presence or absence of these antibodies does not definitively confirm or negate a diagnosis of Merkel cell carcinoma.  

Sometimes, doctors order the following imaging tests to determine if the cancer has spread to other parts of the body:

  • CT scan
  • MRI
  • PET scan

How is Merkel cell carcinoma treated?

Merkel cell carcinoma may be treated in the following ways:  

  • Surgery. The primary treatment for Merkel cell carcinoma is surgery to remove the tumor, plus a wide margin of healthy surrounding skin. Doctors also remove lymph nodes near the site of the cancer, to determine if the cancer has spread.
  • Radiation therapy. Merkel cell carcinoma is very sensitive to radiation. Radiation is used after surgery if the tumor is big. It is also used to “sterilize” the lymph node basin if the Merkel cell has spread to draining lymph nodes. Radiation can also be used if surgery is not possible due to other medical conditions or if a metastatic tumor is causing symptoms.
  • Immunotherapy. If a patient has recurrent Merkel cell carcinoma or advanced disease, immunotherapy is used to help boost the body’s immune system to fight the cancer cells. Immunotherapy has now become the standard of care in advanced disease, as it is highly affective.
  • Chemotherapy, which kills cancer cells, along with some healthy cells, may also be used when immunotherapy is unsuccessful or in patients who cannot receive immunotherapy due to other medical conditions.     

What is the outlook for people with Merkel cell carcinoma?

When Merkel cell carcinoma is discovered and treated early, and hasn’t spread to other parts of the body, about 75% of people live for at least 5 years after diagnosis. The outcomes tend to be worse if the cancer spreads; thus, early detection and treatment are important.  

Because Merkel cell carcinoma can recur, patients may undergo screening every 3 to 6 months for the first two years after treatment, then every 6 to 12 months onward.

What makes Yale Medicine unique in its treatment of Merkel cell carcinoma?

Yale Medicine has been a leader in the field of cancer immunology for decades. In fact, Lieping Chen, MD, PhD, United Technologies Corporation Professor in Cancer Research at Yale Cancer Center, defined the role of a molecule called PD-L1 (previously known as B7-H1) in immune evasion by cancer cells. 

“Drugs that target PD-L1 or its receptor PD-1 have revolutionized cancer care in general, and have had a profound effect on outcomes in advanced Merkel cell carcinoma,” says Dr. Kluger, an investigator on the seminal clinical trial that led to FDA approval for one of these drugs, pembrolizumab.  

Dr. Kluger and her colleague, Yale Medicine dermatopathologist Marcus Bosenberg, MD, PhD, co-direct a large, multi-project, NIH-funded SPORE grant for studying skin cancer, including Merkel cell carcinoma, which provides a platform for clinical translation of laboratory findings.