Epidemiology

Incidence

• Age-adjusted incidence estimated to be 0.24/100,000 person-years in the United States (1)
• Incidence has tripled since 1986, with an average annual increase of 8% (2).
• Highest in the elderly: Median age at diagnosis is 71 years in immunocompetent and 60 years in immunosuppressed (3).
• Increased incidence likely secondary to aging population, increased sun exposure, and number of immunocompromised individuals (2,4)
• Rare, <1% of all skin cancers in the United States
• 1,500 cases diagnosed in 2007 (2)

Etiology and Pathophysiology

• Tumor shares several ultrastructural, morphologic, and immunohistologic features with Merkel cells (slowly adapting fine-touch mechanoreceptors in the basal epidermis) as well as with other extracutaneous neuroendocrine tumors. Despite these shared features from which the tumor was originally named, there is little evidence for direct relationship between Merkel cells and Merkel cell carcinoma (MCC). As such, the term “primary cutaneous neuroendocrine tumor” has been suggested but not yet widely adopted (5).
• Some suggest derivation from immature pluripotent cells in dermis.
• Merkel cell polyomavirus (MCPyV) likely contributes to development of MCC and has been detected in 80% of tumors tested (6,7,8).

Risk Factors

• UV exposure (natural or artificial)
• History of prior skin cancer
• Fair skin
• Age >65 years
• Chronic immune suppression (HIV, leukemia, organ transplantation)
• MCPyV

General Prevention

Avoid sun exposure; early biopsy of suspicious rapidly growing lesion; early referral for further management

Commonly Associated Conditions

Increased risk for developing other malignancies, including lymphomas and other skin cancers