Merkel cell carcinoma is a rare disease in which cancerous cells are found on or just beneath the skin. It usually appears as firm, painless, shiny lumps of skin that usually have rapidly increased in size just prior to diagnosis. These lumps or tumors can be red, pink, or blue and be as small as a quarter of an inch to more than two inches.
Merkel cell carcinoma is usually found on the sun-exposed areas of the head, neck, arms, and legs and occurs mostly in Caucasians who are over 60 years of age, but it can occur in people of other races and ages as well. It grows rapidly and often metastasizes (spreads) to other parts of the body. Even relatively small tumors are capable of metastasizing. When the disease spreads, it tends to spread to nearby lymph nodes and may also spread to the liver, bone, lungs, and brain.
Merkel cell carcinoma does not have a distinctive appearance. It usually develops on sun-exposed skin on the head, neck, or arms. It is painless, firm, and can look like a skin-colored, red, or blue bump. It is usually thought to be a non-cancerous lesion such as a cyst prior to skin biopsy.
While Merkel cell carcinoma is relatively rare, with about 1,000 cases a year in the United States, its incidence has tripled in the past 15 years and it can be lethal in about one-third of the cases. A quick diagnosis and appropriate treatment is necessary to cure this disease.
Most Merkel cell carcinomas are diagnosed with a skin biopsy, to rule out another sun-induced skin cancer or a cyst. In the vast majority of cases, both the doctor and the patient are surprised by the diagnosis of Merkel cell carcinoma.
The diagnosis of Merkel cell carcinoma is made with a skin biopsy, which is examined under the microscope by a pathologist. Special stains are used to distinguish it from other forms of cancer, such as small cell lung cancer, lymphoma, and small cell melanoma. The biopsy will also rule out other sun-induced skin cancers or cysts. Patients seen in consultation at the SCCA typically have their pathology slides sent to us in advance of their appointment for confirmation of the diagnosis.
The exact cause of Merkel cell carcinoma is not known, but people more likely to have it are:
- Over 65 years old
- Have fair skin
- Had extensive sun exposure during their lifetime
- Have chronic immune suppression (had a kidney or heart transplant, or have HIV)
- In 2003, a study of 1,034 patients found the average age of Merkel cell patients was 74 and the most common sites were the head followed by the arms.