Merkel cell cancer overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. ; Associate Editor(s)-in-Chief: Vamsikrishna Gunnam M.B.B.S  Ahmad Al Maradni, M.D. 
Merkel cell carcinoma is a very rare and highly aggressive cutaneous cancer. This cancer is a type of neuroendocrine tumor, like small cell lung cancer. Merkel cell carcinoma is the most serious form of skin cancer. when merkel cell carcinoma metastasized to the lymph nodes, the average 5-year survival rate for a patient with merkel cell carcinoma is less than 50 percent. Recurrence may occur in up to half of all the patients with merkel cell carcinoma. Merkel cell cancer usually occurs on either the face, head, or neck. Patients with merkel cell carcinoma usually present with a rapid growing, firm, painless, red/violaceous skin lesion. Merkel cell carcinoma usually metastasizes first to regional lymph nodes and then to other organs, and spreads to other parts of the body, especially the liver, lungs, brain and bones. The predominant therapy for merkel cell carcinoma is surgical resection, but chemoradiation may also be required in more advanced disease.
Merkel cell was first discovered by Freidrich Sigmund Merkel and also mentioned by Cyril Toker, in 1972.Merkel cell polyomavirus, the pathogen responsible for Merkel cell cancer, was first discovered in 2008.
Merkel cell carcinoma is classified into 3 subgroups: Trabecular, intermediate, and small cell.
It is understood that merkel cell cancer is the result caused by either merkel cell polyomavirus, ultraviolet (UV), radiation exposure and immunosuppression.
Common causes of merkel cell carcinoma include merkel cell polyomavirus, age, skin tone, exposure to sunlight and history of immunosuppression.
Merkel cell cancer must be differentiated from other skin lesions, such as basal cell carcinoma, squamous cell carcinoma, malignant melanoma, lymphoma, vascular tumors, and other benign skin tumors.
Epidemiology and Demographics
The incidence of merkel cell carcinoma ranges from 0.15 to 0.44 per 100,000 individuals. The median age at diagnosis is approximately 65 years. Merkel cell carcinoma is more common among males and individuals of Caucasian race.
Risk factors for the development of merkel cell cancer include old age, male gender, caucasian race, chronic exposure to sunlight, immunodeficiency, and personal history of cancer.
According to the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for skin cancers, including merkel cell cancer.
Natural History, Complications and Prognosis
Merkel cell cancer is an aggressive cutaneous cancer that grows very rapidly. Merkel cell cancer usually metastasizes first to regional lymph nodes. Merkel cell cancer is a highly aggressive tumor with a mortality rate that approaches 30% to 40% within 3 years of diagnosis.
The staging of merkel cell cancer is based on the TNM staging system.
History and Symptoms
Patients with merkel cell carcinoma usually present with a rapid growing, painless, small mass that is typically located on sun exposed area of the body.
Physical exam findings of merkel cell cancer include red/violaceous skin mass that appear in sun exposed areas.
Laboratory findings consistent with the diagnosis of merkel cell cancer include immunohistochemistry, cytogenetic and molecular analysis, and lymph node biopsy. .
CT scan is useful in detecting metastasis to organs and regional lymph nodes in merkel cell carcinoma.
Other Imaging Findings
Positron emission tomography (PET) imaging may be used for the staging of merkel cell cancer.
Other Diagnostic Studies
Other diagnostic studies for merkel cell cancer include skin biopsy, which demonstrates positive cytokeratin-20 , and electron microscopy, which demonstrates granules, and cytoplasmic extensions.
The predominant therapy for Merkel cell cancer is surgical resection. Adjunctive chemoradiation and adjuvant immunotherapy may also be required in more advanced disease.
The majority of cases of Merkel cell cancer are treated with surgery.
Primary prevention of merkel cell cancer includes avoidance of excessive sun exposure and use of sunscreen.
There are no established measures for the secondary prevention of merkel cell cancer.