Merkel cell carcinomas (MCC)
Merkel cell carcinoma (MCC) is a rare and aggressive form of skin cancer that originates in Merkel cells, which are involved in the sensation of touch. This cancer typically manifests as firm, painless nodules that can appear shiny and vary in color from red to blue. MCC is predominantly found on the face, neck, or head, but can also occur on other body parts. While it accounts for less than 1 percent of all skin cancers, it has become the second leading cause of non-melanoma skin cancer deaths, with a high rate of metastasis to lymph nodes and other organs.
Individuals over the age of sixty-five, those with lighter skin, and people with weakened immune systems are at greater risk for developing MCC. The disease's progression is linked to factors such as ultraviolet light exposure and the Merkel cell polyomavirus, which is found in the majority of patients. Diagnosis involves biopsy and imaging tests to assess the cancer's spread, with treatment options ranging from surgical removal to radiation therapy. The prognosis varies significantly, with localized cases showing a better survival rate compared to those diagnosed with metastatic disease. Preventive measures primarily focus on minimizing UV exposure.
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Merkel cell carcinomas (MCC)
ALSO KNOWN AS: Neuroendocrine carcinoma of the skin, trabecular carcinoma, trabecular cancer
RELATED CONDITIONS: Ectodermal dysplasia
DEFINITION: Merkel cell carcinomas (MCC) are fast-growing cancers in Merkel cells found in the deepest part of the outermost skin layer and are associated with the sense of touch. The structure of Merkel cells is characteristic of cells that assist in impulse transmission between an initial stimulus and the nerve impulse that carries messages to the brain. This cancer appears on the face, head, or neck as a firm, painless, shiny bump that can be red, pink, or blue, and it has been found to spread quickly to other parts of the body. Considered rare, MCC has become the second most common cause of non-melanoma skin cancer deaths, with most deaths occurring within three years of diagnosis.
Risk factors: Risk factors include being over the age of sixty-five, a history of repeated or prolonged sun exposure, lighter skin, and previous skin cancer diagnoses. People with weakened immune systems, such as those with human immunodeficiency virus (HIV), patients with organ transplants, and those on medications that suppress the immune system, are at increased risk of developing MCC.
Etiology and the disease process: Although the exact cause of MCC is unknown, ultraviolet radiation from the sun and other sources plays a significant role in its development. One theory proposes that stem cells in the skin become cancerous and take on the characteristics of Merkel cells. Merkel cell polyomavirus, a common virus that lives on the skin, also contributes to the condition—eight out of ten people with MCC test positive for the virus. Genetic abnormalities have been found in the cancer cells, leading to speculation that MCC is genetically linked. MCC grows rapidly, typically beginning on the face (especially around the eye), neck, and head. Metastasis to nearby llymph nodes and other areas of skin, liver, bone, and lungs is common and occurs early in the disease. When MCC spreads to other areas of the skin, the lesions grow rapidly and are flesh-colored to red-purple, firm, and deeper in the skin than the primary lesion.
Incidence: In the United States, around 3,000 people are impacted by MCC each year. Although the number of cases is increasing, it still accounts for less than 1 percent of all skin cancers. The median age at diagnosis is sixty-five. MCC is substantially more common among white people and affects men more often than women.
Symptoms: The primary skin lesions in MCC usually produce no symptoms. They usually occur as solitary, dome-shaped nodules that are smaller than 2 centimeters (cm) in diameter but can be larger than 15 cm. The skin surface is typically shiny, and the color of the lesions is red, pink, or blue. Although they can develop on any skin surface, about 50 percent of cases occur on the head or neck, and 40 percent appear on the arms and legs.
Because metastasis is common with MCC, other symptoms that may be reported include swollen lymph glands and fatigue. New growths, with a different appearance than the primary site, may also be reported.
Screening and diagnosis: Screening for MCC should be performed as part of an annual physical, and people at high risk for MCC should perform routine self-examination. When a nodule is found, a biopsy is necessary to determine its cell type and whether it is benign tissue, MCC, or another form of cancer. If it is MCC, further testing should follow as soon as possible because it spreads rapidly. Additional testing should include a sentinel lymph node biopsy, a complete blood count, liver function tests, and a chest X-ray. Computed tomography (CT) and positron emission tomography (PET) scanning should also be performed to determine the extent of the cancer’s spread.
MCC is divided into three stages depending on the severity of the disease.
- Stage I: The disease is localized to the skin at the primary site.
- Stage IA: The primary lesion is less than or equal to 2 cm.
- Stage IB: The primary lesion is greater than 2 cm.
- Stage II: The cancer involves nearby lymph nodes.
- Stage III: The cancer is found beyond the nearby lymph nodes.
The stage at diagnosis is important in determining the possibility of tumor metastasis, the patient’s treatment options, and prognosis.
Treatment and therapy: Treatment of MCC is based on the stage of the disease at diagnosis. Most commonly, surgery is performed to remove the primary lesion. In wide local excision, the tumor and some normal skin around the lesion’s edges are removed. Mohs surgery removes the tumor but leaves as much healthy tissue as possible. In lymph node dissection, the lymph nodes are removed to test for cancer cells and the spread of the disease. Radiation therapy is usually given to the site of the primary lesion and the lymph nodes. When the cancer has spread beyond the lymph nodes, treatment is mainly palliative to relieve pain. The use of chemotherapy, typically with etoposide and carboplatin, is controversial. Some studies have demonstrated positive results but recommend that it be reserved for metastatic MCC, whereas others have found that, especially with this disease, there was a trend toward decreased survival rates.
Prognosis, prevention, and outcomes: Overall, the two-year survival rate for MCC is 50 to 70 percent. Most recurrences and deaths from this disease occur within the first three years. For patients with localized MCC, more than 70 percent live for five or more years. But in patients with metastasized MCC, the five-year survival rate is one in four. The only prevention for MCC is to reduce exposure to ultraviolet light, including the sun.
Bibliography
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"What Is Merkel Cell Carcinoma?" American Cancer Society, www.cancer.org/cancer/types/merkel-cell-skin-cancer/about/what-is-merkel-cell-carcinoma.html. Accessed 20 June 2024.